bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite
Authors: Hunt Simon A. , Whitaker Matthew L. , Bailey Edward , Mariani Elisabetta , Stan Camelia V. , Dobson David P.
Published: March 2019

In this study, quartz, coesite, and stishovite were deformed concurrently with an olivine reference sample at high pressure and 850 ± 50 °C. Olivine deformed with an effective stress exponent (n) of
, which we interpret to indicate that the Peierls creep deformation mechanism was active in the olivine. Quartz and coesite had very similar strengths and deformed by a mechanism with n =
and
, respectively, which are consistent with previous measurements of power law creep in these phases. Stishovite deformed with n = 
and was stronger than both olivine and the other silica polymorphs. The high stress exponent of stishovite is greater than that typically observed for power law creep, indicating it is probably (but not certainly) deforming by Peierls creep. The rheology of SiO2 minerals appears therefore to be strongly affected by the change in silicon coordination and density from fourfold in quartz and coesite to sixfold in stishovite. If the effect of Si coordination can be generalized, the increase in Si coordination (and density) associated with bridgmanite formation may explain the tenfold to 100‐fold viscosity increase around 660 km depth in the Earth.
Phase Relations of Harzburgite and MORB up to the Uppermost Lower Mantle Conditions: Precise Comparison With Pyrolite by Multisample Cell High‐Pressure Experiments With Implication to Dynamics of Subducted Slabs
Authors: Ishii Takayuki , Kojitani Hiroshi , Akaogi Masaki
Published: March 2019

We determined phase relations of harzburgite and basalt (mid‐ocean ridge basalt, MORB) at 12–28 GPa and 1600–2200 °C with a large number of experiments using a multianvil high‐pressure apparatus. These phase relations were precisely compared with those of pyrolite simultaneously determined by multisample cell technique. The post‐spinel (pSp) transition of harzburgite occurs at 23 GPa and 1600 °C with the boundary slope of −3 ± 1 MPa/°C. The post‐garnet (pGt) transition boundary of MORB, defined as the beginning of the majorite garnet‐bridgmanite transition, is located at 25 GPa and 1600 °C, with a slope of 1.5 ± 1 MPa/°C. The pSp transition of harzburgite occurs at higher pressure by 0.5 GPa at 1600 °C and has the more negative slope than that of pyrolite (−1 ± 1 MPa/°C). The pGt transition of MORB occurs at higher pressure by 3 GPa than the pSp transition of harzburgite. At 1600 °C, the density of pyrolite is smaller than those of harzburgite and MORB before the pSp transition of pyrolite (pyrolite–harzburgite/MORB = −0.17 g/cm3). After the pSp transition of pyrolite, harzburgite has lower densities than that of pyrolite at 22–27 GPa (pyrolite–harzburgite = 0.31 and 0.08 g/cm3 before/after the pSp transition in harzburgite, respectively). On the other hand, the density of MORB becomes the highest among the three rocks above 25 GPa after the pGt transition of MORB (pyrolite–MORB = −0.18 g/cm3). The present density contrasts suggest that harzburgite and MORB may stagnate and accumulate in the transition zone by slab subduction, resulting in that the pyrolitic part of slabs is subducted into the lower mantle.
Experimental Insights Into Fault Reactivation in Gouge‐Filled Fault Zones
Authors: Giorgetti C. , Tesei T. , Scuderi M. M. , Collettini C.
Published: March 2019

Faults in the brittle crust constitute preexisting weakness zones that can be reactivated depending on their friction, orientation within the local stress field, and stress field magnitude. Analytical approaches to evaluate the potential for fault reactivation are generally based on the assumption that faults are ideal planes characterized by zero thickness and constant friction. However, natural faults are complex structures that typically host thick fault rocks. Here we experimentally investigate the reactivation of gouge‐bearing faults and compare the resulting data with theoretical predictions based on analytical models. We simulate preexisting faults by conducting triaxial experiments on sandstone cylinders containing saw‐cuts filled with a clay‐rich gouge and oriented at different angles, from 30° to 80°, to the maximum principal stress. Our results show the reactivation of preexisting faults when oriented at 30°, 40°, and 50° to the maximum principal stress and the formation of a new fracture for fault orientations higher than 50°. Although these observations are consistent with the fault lock‐up predicted by analytical models, the differential stress required for reactivation strongly differs from theoretical predictions. In particular, unfavorable oriented faults appear systematically weaker, especially when a thick gouge layer is present. We infer that the observed weakness relates to the rotation of the stress field within the gouge layer during the documented distributed deformation that precedes unstable fault reactivation. Thus, the assumption of zero‐thickness planar fault provides only an upper bound to the stress required for reactivation of misoriented faults, which might result in misleading predictions of fault reactivation.
Asteroid Visited by Mission Spews Rocks into Space
Authors: Cartier Kimberly
Published: March 2019

Mission scientists observed 11 separate particle ejection events in a 1-month period. They are still trying to figure out what could be causing the particle plumes.
Before Canadian Scientists Can Study Tornadoes, They Have to Find Them
Authors: Kaufman Rachel
Published: March 2019

A yearlong project aims to find more than 150 "missing" tornadoes thought to hit Canada each year.
Flexible photodetectors based on reticulated SWNT/perovskite quantum dot heterostructures with ultrahigh durability
Authors: Zheng Jialu , Luo Chengzhi , Shabbir Babar , Wang Chujie , Mao Wenxin , Zhang Yupeng , Huang Yamin , Dong Yemin , Jasieniak Jacek J. , Pan Chunxu , Bao Qiaoliang
Published: March 2019

Recently, single-walled carbon nanotube (SWNT) films have been regarded as a promising channel material for flexible photodetectors due to their high intrinsic carrier mobility, conductivity, and mechanical flexibility.
Janus triple tripods build up a microporous manifold for HgCl2 and I2 uptake
Authors: He Yonghe , Huang Mengjiao , Deng Xiangling , Shengxian Cheng , Wong Yan-Lung , Hou Yun-Long , He Jun , Zeller Matthias , Xu Zhengtao
Published: March 2019

Three tripods for a versatile molecular scaffold: combining the Janus core for supramolecular recognition and the planar carboxyl tripod for framework construction enables metal uptake and iodine removal applications.
Co-assembled supramolecular hydrogels of doxorubicin and indomethacin-derived peptide conjugates for synergistic inhibition of cancer cell growth
Authors: Mei Leixia , He Suyun , Liu Ziqi , Xu Keming , Zhong Wenying
Published: March 2019

Co-assembly of doxorubicin and a NSAID-based self-assembling peptide conjugate promotes synergistic inhibition of cancer cell growth.
Trifluoromethylthiolative 1,2-difunctionalization of alkenes with diselenides and AgSCF3
Authors: Saravanan Perumal , Anbarasan Pazhamalai
Published: March 2019

An efficient regioselective difunctionalization of alkenes via trifluoromethylthiolation has been accomplished employing diaryl diselenide and AgSCF3 in the presence of BF3·OEt2.
A divergent strategy to synthesize gabosines featuring a switchable two-way aldol cyclization
Authors: Yang Xing , Yuan Po , Shui Feng , Zhou Yuqin , Chen Xiaochuan
Published: March 2019

Mode-switchable aldol cyclization of a diketone precursor enables a novel collective synthesis of divergent gabosine-type carbasugars.
An examination of students' perceptions of the Kekulé resonance representation using a perceptual learning theory lens
Authors: Kim Thomas , Wright L. Kate , Miller Kathryn
Published: March 2019

Students in chemistry often demonstrate difficulty with the principle of resonance. Despite many attempts to mitigate this difficulty, there have been few attempts to examine the root cause of these issues. In this study, students were assessed for their perception of Kekulé structures based on perceptual learning theory, which is grounded in cognitive mechanisms of visual perception. The data from this assessment shows that students are perceiving inappropriate clues from this representation, which infers that the image itself might be an impediment to learning about resonance. Employment of a metarepresentational competence approach was used to address these misperceptions.
A three-dimensional macroporous antimony@carbon composite as a high-performance anode material for potassium-ion batteries
Authors: He Xiao-Dong , Liu Ze-Hua , Liao Jia-Ying , Ding Xiang , Hu Qiao , Xiao Li-Na , Wang Shuo , Chen Chun-Hua
Published: March 2019

A novel three-dimensional macroporous antimony@carbon composite is fabricated by a simple KCl template method with a single bi-functional precursor potassium antimony tartrate.
Room temperature production of graphene oxide with thermally labile oxygen functional groups for improved lithium ion battery fabrication and performance
Authors: Qin Jiadong , Zhang Yubai , Lowe Sean E. , Jiang Lixue , Ling Han Yeu , Shi Ge , Liu Porun , Zhang Shanqing , Zhong Yu Lin , Zhao Huijun
Published: March 2019

We report a room-temperature synthesis method to produce graphene oxide with thermally-labile oxygen functional groups.
Scalable room-temperature synthesis of plum-pudding-like Cs4PbBr6/CsPbBr3 microcrystals exhibiting excellent photoluminescence
Authors: Hu Guomiao , Qin Wenjing , Liu Manman , Ren Xiaoxue , Wu Xiaoming , Yang Liying , Yin Shougen
Published: March 2019

Plum-pudding-like Cs4PbBr6/CsPbBr3 MCs with excellent photoluminescence, good stability and spectral adjustability.
Electronic structure engineering of tin telluride through co-doping of bismuth and indium for high performance thermoelectrics: a synergistic effect leading to a record high room temperature ZT in tin telluride
Authors: Shenoy U. Sandhya , Bhat D. Krishna
Published: March 2019

Resonance states due to Bi and In co-doping, band gap enlargement, and a reduced valence-band offset in SnTe lead to a record high room-temperature ZT.
Performance analysis of multi‐hop multi‐branch frequency‐selective channel for DF relaying
Authors: Rawat Manishika , Lall Brejesh
Published: March 2019

In this work, the authors have explored the average bit error rate (BER) and ergodic capacity (EC) of a frequency‐selective channel consisting of multi‐hop and multi‐branch (MHMB). Each hop consists of multiple paths and signal travels in successive hops using decode and forward (DF) relaying. The channel is assumed to be log‐normal distributed. Numerical integration (NI) formulations based on the Gauss‐quadrature rule representation of the moment generating function of log‐normal distribution have been derived for both average BER and EC for multi‐hop and MHMB cooperative communication framework using maximal ratio combining and selection combining (SC) techniques at receiver. Results are obtained for a variable number of hops and branches. Excellent matching between Monte Carlo simulation and NI plots validate the accuracy of the proposed formulations. The contribution of this work to the existing research scenario is two‐fold: (i) to the best of the authors' knowledge, this is a first attempt to study a generic MHMB framework of a log‐normal distributed frequency‐selective channel. (ii) DF which is a more practical relaying protocol has not been explored till date for analysis of a log‐normal distributed MHMB network. Both of these aspects make this work pertinent.
Coarse NLOS detection algorithm based on discrete power levels
Authors: Qiao Tianzhu , Cheng Lin
Published: March 2019

Indoor localisation has become increasingly important for many services. When the environment is not crowded, i.e. most links between the target and anchors do not suffer from non‐line‐of sight (NLOS) offsets, the centralised time‐difference‐of‐arrival localisation can efficiently estimate the target position. However, such a method does not work in crowded environments unless a large number of anchors are installed, which is unrealistic for many applications. In this case, the objects that block the LOS links can serve as dynamic anchors (e.g. with round trip time‐of‐arrival localisation) to improve positioning accuracy. However, such a method tends to include too many unreliable dynamic anchors in estimation, which will significantly increase the computational complexity (e.g. to detect and discard such unreliable anchors in the NLOS mitigation stage). This study proposes a coarse NLOS detection algorithm based on discrete power levels to efficiently achieve the coarse NLOS mitigation, which automatically discards most unreliable dynamic anchors. The simulation results show that the proposed method can achieve very similar estimation performance as the optimal estimation method in the crowded environment, while analysis shows that it can significantly decrease the computational complexity.
Path loss modification and multi‐user capacity analysis by dynamic rain models for 5G radio communications in millimetre waves
Authors: Zhao Xiongwen , Wang Qi , Geng Suiyan , Zhang Yu , Zhang Jianhua , Li Jingchun
Published: March 2019

Based on outdoor microcellular measurements at 26 and 32 GHz, the path loss models are modified by a proposed dynamic rain model to see the difference of the path loss models between clear and rainy air with respect to rainfall intensities and transceiver distances. Moreover, a dynamic rain cell model for a multi‐user system is developed to investigate the total rain attenuation. The results show that the parameters for floating‐intercept (FI) model have a bigger change with different rainfall intensities than close‐in (CI) model. When considering the dynamic rain model with a different radius and moving speeds, the larger rain cell radius, the larger path loss exponents in CI and FI models, the smaller path loss intercept in FI model and system capacity will be achieved. For a fixed rain cell radius, the larger moving speed of the rain cell, the shorter effective time on the path loss and system capacity will be achieved. In addition, the rain cell has a bigger effect on the path loss exponent, intercept and system capacity at higher frequency band with respect to its size, moving speed, and rainfall intensity.
Automated retinal layer segmentation in OCT images of age‐related macular degeneration
Authors: Chen Zailiang , Li Dabao , Shen Hailan , Mo Yufang , Wei Hao , Ouyang Pingbo
Published: March 2019

Age‐related macular degeneration (AMD) is a common eye disease that causes progressive degeneration of the central vision. The presence of abundant drusen is a common early feature of AMD. Optical coherence tomography (OCT) can provide detailed structure information on drusen. The physiological structure of the retinal epithelium and drusen complex (RPEDC) and the Bruch's membrane (BM) layer boundaries will be influenced by the presence of drusen with AMD. Therefore, drusen quantification is important to diagnose and cure AMD. The authors proposed an automatic method to segment the inner limiting membrane, the retinal pigment epithelium and drusen complex (RPEDC) and BM layer boundaries from OCT images with AMD (termed as deep forest for layer segmentation (DF‐LS)). In their method, image patches are extracted and used to train a deep‐forest model to predict three boundary probability maps. In addition, they modify grapy theory and dynamic programming method to find the layer boundary. Finally, the layer boundary is smoothed by using a smoothing operation. The proposed DF‐LS method is evaluated on three publicly available datasets (one healthy dataset and two AMD dataset). The proposed DF‐LS method can yield superior mean unsigned error with an average error of 0.81 pixel on Tian et al.'s dataset, and 1.35, 1.23 pixel on Chiu et al.'s and Farisu et al.'s dataset, respectively.
Stereoscopic image quality assessment by analysing visual hierarchical structures and binocular effects
Authors: Ding Yong , Zhao Yang , Chen Xiaodong , Zhu Xiaolei , Andrey Krylov
Published: March 2019

In the design of three‐dimensional image processing systems, stereoscopic image quality assessment (SIQA) plays an indispensable role as a performance evaluator and a supervisor, yet the study upon which remains immature due to the complexity of the human visual system (HVS). In this study, a novel SIQA method is proposed by extracting quality‐aware image features according to the properties of the hierarchical structure in the HVS. Especially, the interests of the primary and secondary visual cortex are taken into consideration, so that the image quality representation is constructed in a way both accurate and efficient. Moreover, influences caused by binocular effects including binocular rivalry and binocular visual discomfort are accounted to further improve the performance of the proposed method. The superiority of the proposed method is validated through experiments on public databases in comparison to state‐of‐the‐art works in terms of accuracy and robustness.
Speedy and accurate image super‐resolution via deeply recursive CNN with skip connection and network in network
Authors: Guo Dan , Niu Yanxiong , Xie Pengyan
Published: March 2019

The single image super‐resolution (SISR) methods based on the deep convolutional neural network (CNN) have recently achieved significant improvements in accuracy, advancing the state of the art. However, these deeper models are computationally expensive and require a large number of parameters. Accordingly, they demand more memory and are unsuitable for on‐chip devices. In this study, a novel SISR method using a deeply recursive CNN with skip connections and a network in network structure is proposed. The deeply recursive CNN with skip connections is adopted for the image feature extraction at both local and global levels. Parallelised 1 × 1 CNNs, usually called a network in network structure, are adopted for image reconstruction. Specifically, recursive learning is utilised to control the number of model parameters needed and residual learning is used to ease the difficulty of training. The proposed method performs favourably against the state‐of‐the‐art methods in terms of computational speed and accuracy. It significantly outperforms the previous methods by a large margin, while demanding far fewer parameters. This model requires less memory and is friendly to on‐chip devices.
Successive minutia‐free mosaicking for small‐sized fingerprint recognition
Authors: Chen Jiong , Zhao Heng , Cao Zhicheng , Zhao Weiqiang , Pang Liaojun
Published: March 2019

Small‐sized fingerprint sensors, due to the convenience of integration, are widely used in many applications, especially on smart phones. However, the friction ridge information decreases with the reduction of the collected fingerprint area, resulting in degraded recognition performance. Mosaicking fingerprint impressions has been proved to be effective in boosting the recognition accuracy. Nonetheless, the minutiae‐based mosaicking methods do not work well when there is no sufficient number of minutiae in the overlapping area while existing minutia‐free mosaicking methods are not robust to distortion and result in low mosaicking accuracy. In this study, a novel minutia‐free mosaicking algorithm used the coarse‐to‐fine approach is proposed to obtain a larger fingerprint impression from a couple of small‐sized fingerprint impressions. It consists of three stages: an orientation field‐based coarse alignment, a ridge matching‐based fine alignment, and a nonlinear deformation correction with block‐correspondence Thin Plate Spline model. Experimental results on the XDfinger database demonstrate that the proposed method outperforms the other six mosaicking methods in terms of reject‐to‐fuse rate, registration accuracy, and verification performance. Specifically, in the verification scenario, the equal error rate is reduced from 1.98% of a single impression to 0.41% of two impressions mosaicked by the authors' method.
Image colourisation using deep feature‐guided image retrieval
Authors: Chakraborty Souradeep
Published: March 2019

In this study, the authors aim to colourise a greyscale image using a fully automated framework which retrieves similar images from a reference database and then transfers the colour from the most similar retrieved images to perform colourisation. Inspired by the recent success of deep learning techniques in extracting semantic information from images, they first use fc7 features from AlexNet to retrieve similar images from the reference database. Top‐k retrieved images are considered for colour transfer to the target greyscale image, using various pixel level features. The images which result from the previous step are given a colour enhancement with Reinhard stain normalisation. They follow a pixel‐wise colour saturation based averaging technique to impart colour at pixel level. The final image is rectified using joint bilateral filtering. The resulting coloured images have a realistic appearance, similar in quality to the original coloured images. The proposed method outperforms several previous colourisation techniques, yielding superior performance both quantitatively and qualitatively. The method also enhances low‐contrast images.
Two‐order graph convolutional networks for semi‐supervised classification
Authors: Sichao Fu , Weifeng Liu , Shuying Li , Yicong Zhou
Published: March 2019

Currently, deep learning (DL) algorithms have achieved great success in many applications including computer vision and natural language processing. Many different kinds of DL models have been reported, such as DeepWalk, LINE, diffusionconvolutional neural networks, graph convolutional networks (GCN), and so on. The GCN algorithm is a variant of convolutional neural network and achieves significant superiority by using a one‐order localised spectral graph filter. However, only a one‐order polynomial in the Laplacian of GCN has been approximated and implemented, which ignores undirect neighbour structure information. The lack of rich structure information reduces the performance of the neural networks in the graph structure data. In this study, the authors deduce and simplify the formula of two‐order spectral graph convolutions to preserve rich local information. Furthermore, they build a layerwise GCN based on this two‐order approximation, i.e. two‐order GCN (TGCN) for semi‐supervised classification. With the two‐order polynomial in the Laplacian, the proposed TGCN model can assimilate abundant localised structure information of graph data and then boosts the classification significantly. To evaluate the proposed solution, extensive experiments are conducted on several popular datasets including the Citeseer, Cora, and PubMed dataset. Experimental results demonstrate that the proposed TGCN outperforms the state‐of‐art methods.
Robust and real‐time lane detection filter based on adaptive neuro‐fuzzy inference system
Authors: Küçükmanisa Ayhan , Akbulut Orhan , Urhan Oğuzhan
Published: March 2019

Lane departure warning system used in vehicles has recently become very popular and is about to become a vital component in advanced driver assistance systems. The performance of this system is directly related to lane detection accuracy. In this study, a fuzzy inference system‐based filter for robust lane detection is proposed. The proposed filter has three input parameters which are as follows: the difference between a pixel and its left and right neighbours at a certain distance along the horizontal direction and standard deviation of the pixels between the left and right neighbours. The parameters of the proposed fuzzy filter are determined in a learning phase by taking challenging scenarios such as varying lighting conditions, shadows, and road cracks. Experimental results reveal that the proposed method outperforms existing lane detection filters when integrated into a lane detection system. Since the proposed approach is computationally lightweight, it is suitable for real‐time devices and applications.
Online burr video denoising by learning sparsifying transform
Authors: Han Lili , Li Shujuan , Liu Xiuping , Guo Jiaan
Published: March 2019

The burrs on high‐voltage copper contact leads to point discharge and device damage. Since the high‐voltage copper contact has different machining batch and the contour various which the machine tool remove is not economic and robot usually is used to remove the burrs of high‐voltage copper contact. The first step for robot deburring is to identify burrs. In order to improve the performance of copper contact burr video denoising, this article presents online burr video denoising sparsifying transforms algorithm, which defined two alternative values between the optimal sparse signal and transform learning dictionary, simultaneously, calculated the mean of peak signal‐to‐noise ratio, the mean of execution time, the STD (STandard Deviation), and the VAR (VARiance), accordingly presented an burr video denoising algorithm and compared with state‐of‐the‐art video denoising algorithms. The experiment results show that compared with traditional methods, the burr video denoising algorithm has higher denoising precision, faster denoising speed, and stronger high‐noise‐level processing capacity, and so on. The numeric experiments show that the proposed approach has higher peak signal‐to‐noise ratio and less computation complexity than the existing video denoising methods.
Multi‐objective differential evolution‐based ensemble method for brain tumour diagnosis
Authors: Rezaei Kimia , Agahi Hamed , Mahmoodzadeh Azar
Published: March 2019

Accurate diagnosis of tumour type is a paramount issue in the appropriate treatment of cancer. In this study, a novel multi‐step method, recognising benign and malignant tumour slices in real brain computed tomography (CT) images is proposed. First, image reconstruction is conducted for mixed noise removal using ‘weighted encoding with sparse non‐local regularisation’ technique. For the segmentation purpose, support vector machine (SVM) is performed on CT images. Afterwards, 17 features are extracted, among which multiple important features are selected by the genetic algorithm. These selected features are used as the input to the multilayer perceptron neural network, the weighted kernel width SVM and the k‐nearest neighbours models in tumour classification phase. Following this, the outcomes of mentioned classifiers are combined by means of multi‐objective differential evolution‐based ensemble technique, in order to enhance the classification performance indices. The parameters of this weighted linear combination are found by solving an optimisation problem containing precision and recall as the objective functions. The performance of the implemented approach is compared with the experienced radiologist ground truth and some state‐of‐the‐art methods. The results demonstrate that the ensemble technique achieves high classification rates including the accuracy of 98.65%.
Optimisation of transmission map for improved image defogging
Authors: Tufail Zahid , Khurshid Khawar , Salman Ahmad , Khurshid Khurram
Published: March 2019

Outdoor images taken in foggy weather are not suitable for automation due to low contrast. It is a challenging task to remove fog from images specially when the image contains large sky region. The authors propose dark channel‐based single image defogging technique to estimate atmospheric light which represents the amount of luminance in a scene in the absence of fog. This atmospheric light is used to reconstruct fog‐free image with a transmission map. Transmission map represents the effect of fog with respect to depth in image. In this study, they propose four transmission maps to reconstruct the images with different colour contrast. Proposed method adaptively selects a transmission map depending upon the fog density to reconstruct image with optimal colour contrast. The transmission map is refined by applying Laplacian filter followed by the guided filter. Previously, dark channel prior based methods were considered to be less effective for images with large sky region, but the proposed method reconstructs better result consistently for such images, independent of the density of the fog. Experimental results show that images reconstructed by proposed method are qualitatively better than the previously proposed methods.
Nighttime image enhancement using a new illumination boost algorithm
Authors: Al‐Ameen Zohair
Published: March 2019

Nighttime images are often obtained with low brightness, deficient contrast, and latent colours. Thus, it is important to improve such aspects in order to obtain acceptable quality images. Hence, a new illumination boost algorithm is proposed in this study, in which it can improve the brightness, ameliorate contrast and process the colours of nighttime images properly. Accordingly, the proposed algorithm utilises only a small number of steps and uses several processing concepts to achieve the desired results. Intensive experiments and tests with various natural‐degraded nighttime images are made to validate the performance of the proposed algorithm. In addition, it is compared with eight contemporary algorithms, and the obtained results from these comparisons are evaluated using two specialised image quality assessment metrics. Using the results of the achieved experiments and comparisons, it became evident that the proposed algorithm can provide satisfactory outcomes, in which it provided visually pleasing results and outperformed the comparison algorithms in terms of scored accuracy and visual quality.
Facial expression recognition techniques: a comprehensive survey
Authors: Rajan Saranya , Chenniappan Poongodi , Devaraj Somasundaram , Madian Nirmala
Published: March 2019

Over the past decades, facial expression recognition (FER) has become an interesting research area and achieved substantial progress in computer vision. FER is to detect human emotional state related to biometric traits. Developing a machine based human FER system is a quite challenging task. Various FER systems are developed by analysing facial muscle motion and skin deformation based algorithms. In conventional FER system, the developed algorithms work on the constrained database. In the unconstrained environment, the efficacy of existing algorithms is limited due to certain issues during image acquisition. This study presents a detailed study on FER techniques, classifiers and datasets used for analysing the efficacy of the recognition techniques. Moreover, this survey will assist researchers in understanding the strategies and innovative methods that address the issues in a real‐time application. Finally, the review presents the challenges encountered by FER system along with the future direction.
Wideband MIMO antenna with small ground clearance for mobile terminals
Authors: Deng Changjiang , Lv Xin
Published: March 2019

In this study, a compact planar multiple‐input‐multiple‐output (MIMO) antenna is presented for mobile terminal applications. Various dual‐element configurations are studied using the theory of characteristic modes. The reason of port isolation is explained from the view of modal weighting coefficients. It is found that by arranging the two elements at the top and bottom sides of the board and placing the feed ports at the corners of the board, not only the bandwidth is enhanced but also the port isolation is improved. To further broaden the bandwidth, three branches are well cooperated to provide three λ/4 modes. The optimised no‐ground region (i.e. the ground clearance) of each element only occupies an area of 5 × 30 mm2. The measured bandwidth can cover the 1710–2690 MHz band with the criterion of −10 dB reflection coefficient. The measured port isolation achieves 19 dB without using any decoupling structure. The efficiency is >60% in the entire band. In addition, the user effect on MIMO antenna performance is evaluated.
Novel low profile ultra‐wideband capacitance loaded log‐periodic monopole array with reduced transverse dimension
Authors: He Huan , Chen Yikai , Yang Shiwen
Published: March 2019

A novel low profile log‐periodic array with vertically polarised end‐fire radiation patterns is proposed in this study. It totally consists of 22 antenna elements with three different types of monopole antennas. Specifically, conventional monopoles were utilised at the high end band, while monopoles with different types of top‐hat loadings were designed for lower frequency band operation. Shorting posts are strategically introduced to maintain a good impedance matching at the lower band. A folded microstrip line is printed on the back side of the ground plane to feed the array. The log‐periodic monopole array achieves a very low profile of 0.063 λl, where λl is the wavelength at the lowest operating frequency in free space. Moreover, the array also exhibits an extremely narrow width of 0.075 λl in the transverse dimension, which makes the array an attractive candidate for phased array development along the transverse direction. A prototype of the array is fabricated. Measured results show that the array achieves a minimum realised gain of 4.5 dBi across a wide frequency band of 1.19–11.7 GHz (9.83:1).
New wavelength calibration for echelle spectrographs using Fabry-Pérot etalons
Authors: Cersullo F. , Coffinet A. , Chazelas B. , Lovis C. , Pepe F.
Published: March 2019

Context. The study of Earth-mass extrasolar planets via the radial-velocity technique and the measurement of the potential cosmological variability of fundamental constants call for very-high-precision spectroscopy at the level of δλ/λ <  10−9. Only an accurate wavelength calibration of the spectrograph can guarantee that the aimed precision is achieved over a multi-exposure and multi-epoch data set. Wavelength accuracy is obtained by providing two fundamental ingredients: 1) an absolute and information-rich wavelength source and 2) the ability of the spectrograph and its data reduction of transferring the reference scale (wavelengths) to a measurement scale (detector pixels) in a repeatable manner.

Aims. The goal of this work is to improve the wavelength calibration accuracy of the HARPS spectrograph by combining the absolute spectral reference provided by the emission lines of a thorium-argon hollow-cathode lamp (HCL) with the spectrally rich and precise spectral information of a Fabry-Pérot-based calibration source.

Methods. On the basis of calibration frames acquired each night since the Fabry-Pérot etalon was installed on HARPS in 2011, we constructed a combined wavelength solution that fits simultaneously the thorium emission lines and the Fabry-Pérot lines. The combined fit was anchored to the absolute thorium wavelengths, which provide the “zero-point” of the spectrograph, while the Fabry-Pérot lines were used to improve the (spectrally) local precision. The obtained wavelength solution was verified for auto-consistency and tested against a solution obtained using the HARPS laser-frequency comb (LFC).

Results. The combined thorium+Fabry-Pérot wavelength solution shows significantly better performances compared to the thorium-only calibration. In both cases, the residuals of the LFC line positions to the fitted wavelength solution follow a Gaussian distribution with an rms value of about 14 m s−1 for the combined solution, and twice as large for the thorium-only solution (29 m s−1). Given these positive results, we have applied the new calibrations to scientific frames and tested the radial-velocity residual on three well-known stars: HD 10700, HD 20794, and HD 69830. In all three cases the radial-velocity (RV) scatter could be reduced compared to the measurements using the previous calibration.

Conclusions. The richness of the Fabry-Pérot spectrum helps to improve the wavelength calibration using thorium-argon lamps or extending the wavelength domain of LFCs with limited operational range. The presented techniques will therefore be used in the new HARPS and HARPS-N pipeline, and will be exported to the ESPRESSO spectrograph.
The survey of planetary nebulae in Andromeda (M 31)
Authors: Bhattacharya Souradeep , Arnaboldi Magda , Hartke Johanna , Gerhard Ortwin , Comte Valentin , McConnachie Alan , Caldwell Nelson
Published: March 2019

Context.The Andromeda (M 31) galaxy subtends nearly 100 square degrees on the sky. Any study of its halo must therefore account for the severe contamination from the Milky Way halo stars whose surface density displays a steep gradient across the entire M 31 field of view.

Aims.Our goal is to identify a population of stars firmly associated with the M 31 galaxy. Planetary nebulae (PNe) are one such population that are excellent tracers of light, chemistry, and motion in galaxies. We present a 16 square degree survey of the disc and inner halo of M 31 with the MegaCam wide-field imager at the CFHT to identify PNe, and characterise the luminosity-specific PN number and PN luminosity function (PNLF) in M 31.

Methods.PNe were identified via automated detection techniques based on their bright [O III] 5007 Å emission and absence of a continuum. Subsamples of the faint PNe were independently confirmed by matching with resolvedHubbleSpace Telescope sources from the PanchromaticHubbleAndromeda Treasury and spectroscopic follow-up observations with HectoSpec at the MMT.

Results.The current survey reaches two magnitudes fainter than the previous most sensitive survey. We thus identify 4289 PNe, of which only 1099 were previously known. By comparing the PN number density with the surface brightness profile of M 31 out to ∼30 kpc along the minor axis, we find that the stellar population in the inner halo has a luminosity-specific PN number value that is seven times higher than that of the disc. We measure the luminosity function of the PN population and find a bright cut-off and a slope consistent with previous determinations. Interestingly, it shows a significant rise at the faint end, present in all radial bins covered by the survey. This rise in the M 31 PNLF is much steeper than that observed for the Magellanic clouds and Milky Way bulge.

Conclusions.The significant radial variation of the PN specific frequency value indicates that the stellar population at deprojected minor-axis radii larger than ∼10 kpc is different from that in the disc of M 31. The rise at the faint end of the PNLF is a property of the late phases of the stellar population. M 31 shows two major episodes of star formation and the rise at the faint end of the PNLF is possibly associated with the older stellar population. It may also be a result of varying opacity of the PNe.
The GRAVITY fringe tracker
Authors: Lacour S. , Dembet R. , Abuter R. , Fédou P. , Perrin G. , Choquet É. , Pfuhl O. , Eisenhauer F. , Woillez J. , Cassaing F. , Wieprecht E. , Ott T. , Wiezorrek E. , Tristram K. R. W. , Wolff B. , Ramírez A. , Haubois X. , Perraut K. , Straubmeier C. , Brandner W. , Amorim A.
Published: March 2019

Context. The GRAVITY instrument was commissioned on the VLTI in 2016 and is now available to the astronomical community. It is the first optical interferometer capable of observing sources as faint as magnitude 19 in K band. This is possible through the fringe tracker, which compensates the differential piston based on measurements of a brighter off-axis astronomical reference source.

Aims. The goal of this paper is to describe the main developments made in the context of the GRAVITY fringe tracker. This could serve as basis for future fringe-tracking systems.

Methods. The paper therefore covers all aspects of the fringe tracker, from hardware to control software and on-sky observations. Special emphasis is placed on the interaction between the group-delay controller and the phase-delay controller. The group-delay control loop is a simple but robust integrator. The phase-delay controller is a state-space control loop based on an auto-regressive representation of the atmospheric and vibrational perturbations. A Kalman filter provides the best possible determination of the state of the system.

Results. The fringe tracker shows good tracking performance on sources with coherent K magnitudes of 11 on the Unit Telescopes (UTs) and 9.5 on the Auxiliary Telescopes (ATs). It can track fringes with a signal-to-noise ratio of 1.5 per detector integration time, limited by photon and background noises. During good seeing conditions, the optical path delay residuals on the ATs can be as low as 75 nm root mean square. The performance is limited to around 250 nm on the UTs because of structural vibrations.
The role of dissipative evolution for three-planet, near-resonant extrasolar systems
Authors: Pichierri Gabriele , Batygin Konstantin , Morbidelli Alessandro
Published: March 2019

Early dynamical evolution of close-in planetary systems is shaped by an intricate combination of planetary gravitational interactions, orbital migration, and dissipative effects. While the process of convergent orbital migration is expected to routinely yield resonant planetary systems, previous analyses have shown that the semi-major axes of initially resonant pairs of planets will gradually diverge under the influence of long-term energy damping, producing an overabundance of planetary period ratios in slight excess of exact commensurability. While this feature is clearly evident in the orbital distribution of close-in extrasolar planets, the existing theoretical picture is limited to the specific case of the planetary three-body problem. In this study, we generalise the framework of dissipative divergence of resonant orbits to multi-resonant chains, and apply our results to the current observational census of well-characterised three-planet systems. Focusing on the 2:1 and 3:2 commensurabilities, we identify three three-planet systems, whose current orbital architecture is consistent with an evolutionary history wherein convergent migration first locks the planets into a multi-resonant configuration and subsequent dissipation repels the orbits away from exact commensurability. Nevertheless, we find that the architecture of the overall sample of multi-planetary systems is incompatible with this simple scenario, suggesting that additional physical mechanisms must play a dominant role during the early stages of planetary systems’ dynamical evolution.
Count-based imaging model for the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter
Authors: Massa Paolo , Piana Michele , Massone Anna Maria , Benvenuto Federico
Published: March 2019

The Spectrometer/Telescope for Imaging X-rays (STIX) will study solar flares across the hard X-ray window provided by the Solar Orbiter cluster. Similarly to the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), STIX is a visibility-based imaging instrument that will require Fourier-based image reconstruction methods. However, in this paper we show that as for RHESSI, count-based imaging is also possible for STIX. Specifically, we introduce and illustrate a mathematical model that mimics the STIX data formation process as a projection from the incoming photon flux into a vector consisting of 120 count components. Then we test the reliability of expectation maximization for image reconstruction in the case of several simulated configurations that are typical of flare morphology.
OsAGO2
controls ROS production and the initiation of tapetal PCD by epigenetically regulating
OsHXK1
expression in rice anthers
Authors: Zheng Shaoyan , Li Jing , Ma Lu , Wang Hailong , Zhou Hai , Ni Erdong , Jiang Dagang , Liu Zhenlan , Zhuang Chuxiong
Published: March 2019

Proteins of the ARGONAUTE (AGO) family function in the epigenetic regulation of gene expression. Although the rice (
Oryza sativa
) genome encodes 19 predicted AGO proteins, few of their functions have thus far been characterized. Here, we show that the AGO protein OsAGO2 regulates anther development in rice.
OsAGO2
was highly expressed in anthers. Knockdown of
OsAGO2
led to the overaccumulation of reactive oxygen species (ROS) and abnormal anther development, causing premature initiation of tapetal programmed cell death (PCD) and pollen abortion. The expression level of
Hexokinase 1
(
OsHXK1
) increased significantly, and the methylation levels of its promoter decreased, in plants with knocked-down
OsAGO2
expression. Overexpression of
OsHXK1
also resulted in the overaccumulation of ROS, premature initiation of PCD, and pollen abortion. Moreover, knockdown of
OsHXK1
restored pollen fertility in
OsAGO2
knockdown plants. Chromatin immunoprecipitation assays demonstrated that OsAGO2 binds directly to the
OsHXK1
promoter region, suggesting that
OsHXK1
is a target gene of OsAGO2. These results indicate that OsHXK1 controls the appropriate production of ROS and the proper timing of tapetal PCD and is directly regulated by OsAGO2 through epigenetic regulation.
Activation of the NF-κB Pathway and Heterozygous Deletion of TNFAIP3 (A20) Confer Superior Survival in Extranodal Natural Killer/T-Cell Lymphoma, Nasal Type
Authors: Liu Fang , Zheng Jun-Ping , Wang Lu , Zhao Dan-Hui , Li Ming-Yang , Wang Ying-Mei , Liu Yang , Ma Jing , Zeng Nai-Yan , Liu Hong-Xiang , Liang Rong , Guo Shuang-Ping , Wang Zhe , Yan Qing-Guo
Published: March 2019

Objectives

To investigate the role of TNFAIP3 deletions and NF-κB activation in extranodal natural killer/T-cell lymphoma (ENKTCL), nasal type.

Methods

In total, 138 patients with ENKTCL were included. Activation of NF-κB pathway and expression of TNFAIP3 (A20) were examined by immunohistochemistry. TNFAIP3 was analyzed for deletions using FICTION (fluorescence immunophenotyping and interphase cytogenetics as a tool for investigating neoplasms), for mutations using Sanger sequencing, and for promoter methylation using methylation-specific sequencing.

Results

NF-κB pathway activation was observed in 31.2% of cases (43/138), TNFAIP3 expression was negative in 15.2% of cases (21/138), and heterozygous TNFAIP3 deletion was observed in 35% of cases (35/100). TNFAIP3 exons 2 to 9 mutations and promoter methylation were not observed. Kaplan-Meier analysis showed patients with NF-κB pathway activation or TNFAIP3 heterozygous deletion to have a longer overall survival.

Conclusions

Our study demonstrated that NF-κB activation and TNFAIP3 heterozygous deletion confer superior survival in patients with ENKTCL.
Counterpoint: Keeping the Demons at Bay When Handling Time-Varying Exposures—Beyond Avoiding Immortal Person-Time
Authors: Edwards Jessie K , Htoo Phyo T , Stürmer Til
Published: March 2019

The potential for immortal time bias is pervasive in epidemiologic studies with left truncation or time-varying exposures. Unlike other biases in epidemiologic research (e.g., measurement bias, confounding due to unmeasured factors, and selection based on unmeasured predictors of the outcome), immortal time bias can and should be avoided by the correct assignment of person-time during follow up. However, even when handing person-time correctly, allowing late entry into a study or into an exposure group can open the door to more insidious sources of bias, some of which we explore here. Clear articulation of the study question, including the treatment plans of interest, can provide navigation around these sources of bias and elucidate the assumptions needed for inference given the available data. Here, we use simulated data to illustrate the assumptions required under various approaches to estimate the effect of a time-varying treatment and describe how these assumptions relate to the assumptions necessary to estimate single sample rates and risks in settings with censoring and truncation.