Search

Elastocaloric cooling using shape memory alloys is a promising candidate for next-generation environmentally friendly refrigeration. The temperature lift (Tlift), that is, the ability of the cooling device to transfer heat from a low-temperature source to a high-temperature sink, is a critical performance indicator. However, increasing the Tlift of existing elastocaloric devices is difficult due to the narrow temperature window across which the individual elastocaloric materials exhibit superelasticity (for example, ≤50 K for NiTi shape memory alloys). Here we construct a multi-material cascade elastocaloric cooling device using NiTi with three different temperatures at which the martensite-to-austenite transition is completed, also called austenite finish temperature. By matching the working temperature distribution of the NiTi units with their austenite finish temperatures, we expand the device’s superelastic temperature window to over 100 K and achieved a Tlift of 75 K on the water side. This work demonstrates the great potential of multi-material cascade elastocaloric regenerators for space cooling in the near future. © The Author(s), under exclusive licence to Springer Nature Limited 2024.; Elastocaloric cooling, an emerging refrigeration technology, has so far yielded limited performance in devices. Zhou et al. increase the temperature lift of such devices to 75 K by combining three NiTi elastocaloric materials with different phase-transition temperatures. © The Author(s), under exclusive licence to Springer Nature Limited 2024..

In the version of the article initially published, the Abstract did not include the phrase “commercially-available” which has now been added to the sentence “(for example, ≤50 K for commercially-available NiTi shape memory alloys)”. In the “Construction of multi-material cascade elastocaloric device” section, a new ref. 21 (Zhang, J. et al. Highly efficient grooved NiTi tube refrigerants for compressive elastocaloric cooling. Appl. Therm. Eng. 228, 120439 (2023). https://doi.org/10.1016/j.applthermaleng.2023.120439) has been added to the sentence ending “…whose specific heat transfer area (12.5 cm2 g−1) is one of the largest among all existing compression-based elastocaloric devices (Supplementary Fig. 2)”. The same reference has been added as ref. 13 in the Supplementary information. Additionally, Supplementary Fig. 2 has been amended with the addition of a histogram bar labelled “ATE 2023” and four new sentences at the end of the figure caption. These changes have been made to the HTML and PDF versions of the article.

Elastocaloric (eC) cooling using shape memory alloy (SMA) with zero direct carbon emission is a promising alternative of traditional vapor-compression technology. Compressive eC refrigeration prototype (ERP) performs high fatigue life but suffers from the limited cooling performance. Many studies focus on enhancing the heat transfer property of compressive eC regenerators to improve the specific cooling power (SCP). However, reducing the SCP loss is also essential for developing high-cooling-performance compressive ERPs but has not been given sufficient attention. In this study, we revealed that the force holder widely used in compressive ERPs works as an inactive section that dramatically reduce the SCP produced by the NiTi SMA active section. Numerical heat transfer simulations and experiments were conducted to study the impact of the inactive section on the SCP at varied operation parameters. Nondimensionalized governing equations of the numerical model revealed that the volume ratio (Volnon) of the fluid channel of the inactive section to that of the active section is the determinant geometric parameter for the SCP decrease. Numerical results show that, larger operation frequency fERP, smaller dimensionless fluid velocity V* and system temperature span (∆Tspan) lead to more pronounced decreases in SCPnon (ratio of the SCP to ideal SCPideal at Volnon = 0) as the Volnon increases. It also indicates that the Volnon should be minimized to better < 0.08 for achieving excellent SCPnon > 0.95. Experiments validate that the regenerator with a reduced Volnon = 0.08 exhibits a notable increase of 30.8% and 66.7% in zero-∆Tspan SCP and no-load ∆Tspan respectively, in comparison to the regenerator with Volnon = 0.5. Therefore, minimizing the Volnon of the inactive section via reducing the length and diameter of the fluid channel inside the force holder is necessary and highly recommended for developing high-performance compressive ERPs.

Space cooling consumes large amounts of electricity, and the market-dominant vapor-compression refrigeration relies on high global-warming-potential refrigerants. Elastocaloric cooling using shape memory alloys is a promising alternative because of its high energy efficiency and greenhouse-gas-free properties. However, the limited system temperature span and cooling power in existing elastocaloric devices restrict the commercialization of this technology. We address the challenge by designing and fabricating a tubular NiTi of spiral cross-section to increase the specific heat transfer area and by developing a cascade-unit architecture to increase the length of the regenerator without Euler buckling under compression. In terms of the temperature span and cooling power metrics, our device surpasses those of all existing elastocaloric devices, demonstrating a great potential for space cooling in the near future.

Elastocaloric (eC) cooling without environmental issues has been a promising substitute for the conventional vapor-compression refrigeration. Commercial superelastic NiTi shape memory alloy tubes show large elasto-caloric cooling capacity and ultrahigh fatigue life under cyclic compression but suffer from the limited specific heat transfer area (Aht) and insufficient cooling performance. Up to now, compressive NiTi tube eC refrigerant with Aht larger than 1 m2 Kg-1 has not been available due to the easy buckling problem. In this work, the buckling-free vertically and spirally grooved NiTi tubes (VGT and SGT) with Aht of 1.04 m2 Kg-1 and 1.25 m2 Kg-1 respectively are developed as the compressive eC refrigerants. The VGT and SGT are fabricated by the slow -feeding wire electric discharge machining based on the bared NiTi tubes. Then a compressive eC refrigeration prototype (ERP) is built to experimentally characterize the specific cooling power (SCP) and system temperature span (ATspan) of the grooved tubes. Under the regenerative flow configuration, the VGT and SGT achieve large zero-ATspan SCP of 2.18 W g- 1 and 2.61 W g- 1 at the operation frequency (fERP) = 0.5 Hz. Besides, the VGT and SGT produce maximum no-cooling-load ATspan of 25.2 K and 27.7 K respectively at fERP = 0.417 Hz. The experimental SCP and ATspan exceed most of the reported eC regenerators and there are still rooms for enhancing the cooling results by improving the ERP in future. Overall, the developed VGT and SGT with large Aht records and excellent cooling performance show big potentials of heat transfer structure design in developing highly efficient eC devices.

Solid-state elastocaloric cooling is increasingly recognized as preferred cooling technology to conventional vapor compressions without using coolants that are volatile atmospheric pollutants or greenhouse gases with global warming potential. However, the specific cooling power (SCP) of current prototypes has yet to be improved in meeting practical requirements. In this work, tubular nickel-titanium (NiTi) elastocaloric regenerators with enhanced heat transfer structures were proposed in order to increase cooling performance in compression-loaded regenerative systems. A numerical model was developed to evaluate this cooling performance. Using a nondimensional analysis of the governing equations, the model simplifies the investigation of the design and operation parameters and greatly reduces the computation complexity of the regenerative elastocaloric cooling systems. As a demonstration, the design principles have been applied to yield an elastocaloric regenerator of spiral-shaped tubular structures, which improves the maximum SCP and maximum temperature span by 186% and 146% respectively, compared to a plain tube design, proving that the numerical model provides a promising pathway for developing energy-efficient elastocaloric cooling systems. © 2023 Elsevier Ltd

Introgression can be an important source of new alleles for adaption under rapidly changing environments, perhaps even more important than standing variation. Though introgression has been extensively studied in many plants and animals, key questions on the underlying mechanisms of introgression still remain unanswered. In particular, we are yet to determine the genomic distribution of introgressed regions along the genome; whether the extent and patterns of introgression are influenced by ecological factors; and when and how introgression contributes to adaptation. Here, we generated high-quality genomic resources for two sympatric widespread Asian oak species, Quercus acutissima and Q. variabilis, sampled in multiple forests to study introgression between them. We show that introgressed regions are broadly distributed across the genome. Introgression was affected by genetic divergence between pairs of populations and by the similarity of the environments in which they live-populations occupying similar ecological sites tended to share the same introgressed regions. Introgressed genomic footprints of adaptation were preferentially located in regions with suppressed recombination rate. Introgression probably confers adaptation in these oak populations by introducing allelic variation in cis-regulatory elements, in particular through transposable element insertions, thereby altering the regulation of genes related to stress. Our results provide new avenues of research for uncovering mechanisms of adaptation due to hybridization in sympatric species. Introgression is an important source of genetic variation. Analysing genomes of two sympatric widespread Asian oak species, the authors find introgression across the genome and signatures of adaptive introgression in regions with suppressed recombination rate.

Elastocaloric refrigeration using superelastic NiTi shape memory alloys (SMAs) has attracted much attention recently because it has a large energy saving potential, no environmental effects, and a low cost. Achieving the continuous operating of elastocaloric devices, i.e., separating the cold and hot areas on the NiTi alloys physically, helps the efficient release and absorption of heat and avoid the reciprocal parts and intervals of outputs in the system. In this paper, an analytical model and proof-of-concept experiments for continuous operating (elasto)caloric devices are presented. The experimental concept was developed based on a set of rotating NiTi sheets with which the copper heat sink and heat source contact cyclically.

Developing novel heat transfer surface structure on NiTi shape memory alloy tubes has big potential to enhance the elastocaloric cooling performance. In this work, an internally grooved superelastic NiTi tube (outer diameter 5 mm, wall thickness 1 mm and length 50 mm) is designed and fabricated as the refrigerant in a compressive regenerative elastocaloric cooling prototype. The geometric parameters of the longitudinal grooves (groove width, groove depth, and groove spacing) are optimized by a numerical heat transfer simulation. A buckling-prevention frame is developed to ensure uniform compression of the NiTi tube in the cooling prototype. Compared with the ungrooved tube of the same size, the specific internal heat transfer area of the grooved NiTi tube (3.44 mm−1) is increased by 360%, producing 53% larger specific cooling power (1.30 W g−1) and 33% larger maximum system temperature lift (8 K). With the buckling-prevention frame, the grooved NiTi tube endures 2 million reversible phase transition cycles under the compressive stress of 800 MPa in the prototype. Such significantly enhanced cooling power of the grooved NiTi tube with high fatigue life demonstrates the critical roles of heat transfer surface structure and buckling prevention in enhancing the elastocaloric cooling performance under compression. © 2022 Elsevier Ltd

The elastocaloric refrigeration utilizing Shape Memory Alloys (SMAs) has been actively pursued as an alternative cooling technology to the traditional vapor compression. Many research efforts have been focusing on the thermomechanical cycles, material properties, and fatigue life of the SMAs. However, less effort has been made to achieve optimal heat transfer performance of the entire system. In this work, for the first time, we introduce a porous regenerative heat exchanger to a tube-based compression-loaded elastocaloric cooling device for enhanced cooling performance without compromising its fatigue life. A convective regenerator made of a porous structure is proposed for better thermal coupling between the nickel-titanium (Ni-Ti) tube and the heat transfer fluids. A quasi-1D numerical model has been developed to predict the elastocaloric cooling performance and optimize the heat transfer structures. We demonstrate, at specific operating conditions, the optimized elastocaloric regenerator design can improve the Specific Cooling Power (SCP) and Coefficient of Performance (COP) by 50% and 45%, respectively, as compared to a bare tube design. The numerical framework developed in this work offers a systematic investigation of complex regenerative heat exchanger systems and a detailed understanding of the design parameters that are vital for prototype development.

The elastocaloric refrigeration utilizing Shape Memory Alloys (SMAs) has been actively pursued as an alternative cooling technology to the traditional vapor compression. Many research efforts have been focusing on the thermomechanical cycles, material properties, and fatigue life of the SMAs. However, less effort has been made to achieve optimal heat transfer performance of the entire system. In this work, for the first time, we introduce a porous regenerative heat exchanger to a tube-based compression-loaded elastocaloric cooling device for enhanced cooling performance without compromising its fatigue life. A convective regenerator made of a porous structure is proposed for better thermal coupling between the nickel-titanium (Ni-Ti) tube and the heat transfer fluids. A quasi-1D numerical model has been developed to predict the elastocaloric cooling performance and optimize the heat transfer structures. We demonstrate, at specific operating conditions, the optimized elastocaloric regenerator design can improve the Specific Cooling Power (SCP) and Coefficient of Performance (COP) by 50% and 45%, respectively, as compared to a bare tube design. The numerical framework developed in this work offers a systematic investigation of complex regenerative heat exchanger systems and a detailed understanding of the design parameters that are vital for prototype development.

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

The elastocaloric refrigeration utilizing Shape Memory Alloys (SMAs) has been actively pursued as an alternative cooling technology to the traditional vapor compression. Many research efforts have been focusing on the thermomechanical cycles, material properties, and fatigue life of the SMAs. However, less effort has been made to achieve optimal heat transfer performance of the entire system. In this work, for the first time, we introduce a porous regenerative heat exchanger to a tube-based compression-loaded elastocaloric cooling device for enhanced cooling performance without compromising its fatigue life. A convective regenerator made of a porous structure is proposed for better thermal coupling between the nickel-titanium (Ni-Ti) tube and the heat transfer fluids. A quasi-1D numerical model has been developed to predict the elastocaloric cooling performance and optimize the heat transfer structures. We demonstrate, at specific operating conditions, the optimized elastocaloric regenerator design can improve the Specific Cooling Power (SCP) and Coefficient of Performance (COP) by 50% and 45%, respectively, as compared to a bare tube design. The numerical framework developed in this work offers a systematic investigation of complex regenerative heat exchanger systems and a detailed understanding of the design parameters that are vital for prototype development.

Background During the cardiac cycle, there is a multi-phasic bidirectional longitudinal movement (LMov) of the intima-media complex of large arteries, i.e. along the arteries. On the left side the common carotid artery (CCA) arises directly from the aortic arc, whereas on the right side the CCA originate from the innominate artery. Aim The aim of this study was to compare LMov of the left and right CCA of healthy subjects to investigate whether the difference in anatomy is of importance for LMov. Material and Methods The CCAs of 93 healthy subjects were investigated using in-house developed ultrasound methods. Results Although the basic pattern were the same in the majority of subjects, several phases of LMov were significantly larger on the left side (the first retrograde phase, p = 0.0006; the second antegrade, "returning" phase, p < 0.00001; and the rapid retrograde phase of movement at the end of the cardiac cycle, p < 0.000001). In contrast, no significant side-difference in the amplitude of the first antegrade movement was seen. The maximal (peak-to-peak) LMov was significantly larger on the left side (p = 0.002). Discussion and Conclusion The side-differences found in LMov may be related to the difference in anatomy, including possible difference in distance to the heart and especially the presence of an extra bifurcation on the right side. Our data provide an important base for the further study of the relation between LMov and cardiovascular risk factors and atherosclerosis., Funding Agencies|Heart Lung Foundation, SwedenSwedish Heart-Lung Foundation; Medical Faculty; Lund University; Swedish Research CouncilSwedish Research CouncilEuropean Commission; Skane County Research Council; Skane University Hospital; Region Ostergotland

Musical instruments recognition is a widely used application for music information retrieval. As most of previous musical instruments recognition dataset focus on western musical instruments, it is difficult for researcher to study and evaluate the area of traditional Chinese musical instrument recognition. This paper propose a traditional Chinese music dataset for training model and performance evaluation, named ChMusic. This dataset is free and publicly available, 11 traditional Chinese musical instruments and 55 traditional Chinese music excerpts are recorded in this dataset. Then an evaluation standard is proposed based on ChMusic dataset. With this standard, researchers can compare their results following the same rule, and results from different researchers will become comparable.

The presence of proper wrinkles is important while modeling realistic virtual garments. Unlike previously used full 3D information methods, our approach achieves detailed garment generation from a single image. First, we retrieve a garment image similar to the initial virtual garment based on content-based image retrieval (CBIR) method. Then, we preprocess the image with a combination of human body reshaping, image segmentation and shape recovery, to obtain the 3D wrinkle details. Finally, the garment height are synthesized into the virtual garment. For better suit the posture of the human body, excess garment energy are released to remove the unmatched wrinkles. We apply our method to various styles of virtual garments, and it enable virtual characters in general pose to be dressed in these garments and complete wrinkle generation. Compared with existing garment modeling methods, the experimental results show that the proposed method could quickly capture the realistic wrinkles of virtual garments with less manual operation and achieve more realistic wrinkles for virtual garments.

We present a dual adaptive garment slice adjustment technique for automatic resizing of apparel products with variant body shapes, and this technique can quickly generate clothed characters. Our first contribution is to propose a novel fit evaluation method. When a 2D garment pattern and a 3D draped garment have the same triangle topology connection, we calculate the shape variable of each triangle and output heat map simultaneously. For sewing a pattern to a newly targeted human body, we propose a fully automatic adjustment method that conforms to the body structure and is composed of two stages. In the coarse auto adjustment (CAA) stage, we propose a method of controlling the size of a garment by the length of a bounding box in five parts of the human body. Then, the garment pattern is automatically adjusted using the measured dimension, by stretching or shrinking. In the fine auto adjustment (FAA) stage, boundary vertices control the shape in the adjustment process. For better matching with the body, the vertices of the garment pattern boundary are relocated with the calculated moving distance and moving direction. As demonstrated in the results, our method enables fully automatic adjustment, preserving the original pattern style of garments between characters with vastly body shapes. Compared with the state-of-art 2D editing method, our proposed approach leads to time saving, and it achieves realistic garment effect compared to auto fitting methods., Arsineh Boodaghian Asl student informatik

Background: During software maintenance and development, the comprehension of program code is key to success. High-quality comments can help us better understand programs, but they're often missing or outmoded in today's programs. Automatic code summarization is proposed to solve these problems. During the last decade, huge progress has been made in this field, but there is a lack of an up-to-date survey. Aims: We studied publications concerning code summarization in the field of program comprehension to investigate state-of-the-art approaches. By reading and analyzing relevant articles, we aim at obtaining a comprehensive understanding of the current status of automatic code summarization. Method: In this paper, we performed a systematic literature review over the automatic source code summarization field. Furthermore, we synthesized the obtained data and investigated different approaches. Results: We successfully collected and analyzed 41 selected studies from the different research communities. We exhaustively investigated and described the data extraction techniques, description generation methods, evaluation methods and relevant artifacts of those works. Conclusions: Our systematic review provides an overview of the state of the art, and we also discuss further research directions. By fully elaborating current approaches in the field, our work sheds light on future research directions of program comprehension and comment generation.

More and more users and developers are using Issue Tracking Systems (ITSs) to report issues, including bugs, feature requests, enhancement suggestions, etc. Different information, however, is gathered from users when issues are reported on different ITSs, which presents considerable challenges for issue classification tools to work effectively across the ITSs. Besides, bugs often take higher priority when it comes to classifying the issues, while existing approaches to issue classification seldom focus on distinguishing bugs and the other non-bug issues, leading to suboptimal accuracy in bug identification. In this paper, we propose a deep learning-based approach to automatically identify bug-reporting issues across various ITSs. The approach implements the k-NN algorithm to detect and correct misclassifications in data extracted from the ITSs, and trains an attention-based bi-directional long short-term memory (ABLSTM) network using a dataset of over 1.2 million labelled issues to identify bug reports. Experimental evaluation shows that our approach achieved an F-measure of 85.6\% in distinguishing bugs and other issues, significantly outperforming the other benchmark and state-of-the-art approaches examined in the experiment.