1,532 research outputs found

    The Physics and Mass Assembly of distant galaxies with the E-ELT

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    One of the main science goal of the future European Extremely Large Telescope will be to understand the mass assembly process in galaxies as a function of cosmic time. To this aim, a multi-object, AO-assisted integral field spectrograph will be required to map the physical and chemical properties of very distant galaxies. In this paper, we examine the ability of such an instrument to obtain spatially resolved spectroscopy of a large sample of massive (0.1<Mstellar<5e11Mo) galaxies at 2<z<6, selected from future large area optical-near IR surveys. We produced a set of about one thousand numerical simulations of 3D observations using reasonable assumptions about the site, telescope, and instrument, and about the physics of distant galaxies. These data-cubes were analysed as real data to produce realistic kinematic measurements of very distant galaxies. We then studied how sensible the scientific goals are to the observational (i.e., site-, telescope-, and instrument-related) and physical (i.e., galaxy-related) parameters. We specifically investigated the impact of AO performance on the science goal. We did not identify any breaking points with respect to the parameters (e.g., the telescope diameter), with the exception of the telescope thermal background, which strongly limits the performance in the highest (z>5) redshift bin. We find that a survey of Ngal galaxies that fulfil the range of science goals can be achieved with a ~90 nights program on the E-ELT, provided a multiplex capability M Ngal/8.Comment: 21 pages, 13 figures, 7 tables. Accepted for publication in MNRA

    Automatic Image Segmentation by Dynamic Region Merging

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    This paper addresses the automatic image segmentation problem in a region merging style. With an initially over-segmented image, in which the many regions (or super-pixels) with homogeneous color are detected, image segmentation is performed by iteratively merging the regions according to a statistical test. There are two essential issues in a region merging algorithm: order of merging and the stopping criterion. In the proposed algorithm, these two issues are solved by a novel predicate, which is defined by the sequential probability ratio test (SPRT) and the maximum likelihood criterion. Starting from an over-segmented image, neighboring regions are progressively merged if there is an evidence for merging according to this predicate. We show that the merging order follows the principle of dynamic programming. This formulates image segmentation as an inference problem, where the final segmentation is established based on the observed image. We also prove that the produced segmentation satisfies certain global properties. In addition, a faster algorithm is developed to accelerate the region merging process, which maintains a nearest neighbor graph in each iteration. Experiments on real natural images are conducted to demonstrate the performance of the proposed dynamic region merging algorithm.Comment: 28 pages. This paper is under review in IEEE TI

    Influence of Ground Rotations on the Seismic Response of Building Structures

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    Despite being studied for over four decades, seismic design codes still fail to incorporate ground rotations in analysis and design. The primary reason is the currently installed accelerometers' inability to measure ground rotation. In addition, installing sensors to measure ground rotations on a large scale is not feasible anytime soon. So, researchers have relied on indirect methods to derive rotational motions from translational records such as single station, multiple station procedures, and so on. However, these methods are unreliable during near-field events where the instruments can themselves rotate. This paper utilizes the application of high-performance computing (HPC) to extract ground rotations in light of these shortcomings. Due to recent advancements in HPC, the simulation of strong near-field events with high accuracy and high-frequency resolution is possible. This paper implements the newly developed Earthquake Simulation (EQSIM) fault-to-structure framework that uses an emerging GPU-based exascale computer platform. The simulation workflow consists of two steps. Initially, a 3D geophysical model representing a large domain of earth is developed, and the model is analyzed in SW4 fourth-order wave propagation code for two earthquake scenarios, Strike-slip and Reverse-thrust. Then, the ground motions extracted from the first step, including the rotational motion, are used to drive the engineering model of fixed-base and soil-structure interaction systems (SSI) through Domain Reduction Method (DRM). For this purpose, four canonical steel moment frame structures of 3-, 9-,20-, and 40-story are modeled in OpenSees. Finally, nonlinear time history analyses are performed to study the effect of ground rotation on the response of the considered structures. Results indicate that the ground rotations can significantly increase the buildings' inter-story drifts, producing additional amplification when SSI is included. The impact of ground rotation is dictated by the fundamental natural frequency of the building along with the frequency and phase content of input motions

    A Hierarchical Representation Network for Accurate and Detailed Face Reconstruction from In-The-Wild Images

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    Limited by the nature of the low-dimensional representational capacity of 3DMM, most of the 3DMM-based face reconstruction (FR) methods fail to recover high-frequency facial details, such as wrinkles, dimples, etc. Some attempt to solve the problem by introducing detail maps or non-linear operations, however, the results are still not vivid. To this end, we in this paper present a novel hierarchical representation network (HRN) to achieve accurate and detailed face reconstruction from a single image. Specifically, we implement the geometry disentanglement and introduce the hierarchical representation to fulfill detailed face modeling. Meanwhile, 3D priors of facial details are incorporated to enhance the accuracy and authenticity of the reconstruction results. We also propose a de-retouching module to achieve better decoupling of the geometry and appearance. It is noteworthy that our framework can be extended to a multi-view fashion by considering detail consistency of different views. Extensive experiments on two single-view and two multi-view FR benchmarks demonstrate that our method outperforms the existing methods in both reconstruction accuracy and visual effects. Finally, we introduce a high-quality 3D face dataset FaceHD-100 to boost the research of high-fidelity face reconstruction. The project homepage is at https://younglbw.github.io/HRN-homepage/.Comment: Accepted by CVPR202

    The Origin And Loss Of Periodic Patterning In The Turtle Shell

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    The origin of the turtle shell over 200 million years ago greatly modified the amniote body plan, and the morphological plasticity of the shell has promoted the adaptive radiation of turtles. The shell, comprising a dorsal carapace and a ventral plastron, is a layered structure formed by basal endochondral axial skeletal elements (ribs, vertebrae) and plates of bone, which are overlain by keratinous ectodermal scutes. Studies of turtle development have mostly focused on the bones of the shell; however, the genetic regulation of the epidermal scutes has not been investigated. Here, we show that scutes develop from an array of patterned placodes and that these placodes are absent from a soft-shelled turtle in which scutes were lost secondarily. Experimentally inhibiting Shh, Bmp or Fgf signaling results in the disruption of the placodal pattern. Finally, a computational model is used to show how two coupled reaction-diffusion systems reproduce both natural and abnormal variation in turtle scutes. Taken together, these placodal signaling centers are likely to represent developmental modules that are responsible for the evolution of scutes in turtles, and the regulation of these centers has allowed for the diversification of the turtle shell
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