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Yuhan Wang

Publications and source records attributed to Yuhan Wang.

171 records · Page 10Linked to original sources

CurricularFace: Adaptive Curriculum Learning Loss for Deep Face Recognition

As an emerging topic in face recognition, designing margin-based loss functions can increase the feature margin between different classes for enhanced discriminability. More recently, the idea of mining-based strategies is adopted to emphasize the misclassified samples, achieving promising results. However, during the entire training process, the prior methods either do not explicitly emphasize the sample based on its importance that renders the hard samples not fully exploited; or explicitly emphasize the effects of semi-hard/hard samples even at the early training stage that may lead to convergence issue. In this work, we propose a novel Adaptive Curriculum Learning loss (CurricularFace) that embeds the idea of curriculum learning into the loss function to achieve a novel training strategy for deep face recognition, which mainly addresses easy samples in the early training stage and hard ones in the later stage. Specifically, our CurricularFace adaptively adjusts the relative importance of easy and hard samples during different training stages. In each stage, different samples are assigned with different importance according to their corresponding difficultness. Extensive experimental results on popular benchmarks demonstrate the superiority of our CurricularFace over the state-of-the-art competitors.

cs.CV↗

Intelligent Home 3D: Automatic 3D-House Design from Linguistic Descriptions Only

Home design is a complex task that normally requires architects to finish with their professional skills and tools. It will be fascinating that if one can produce a house plan intuitively without knowing much knowledge about home design and experience of using complex designing tools, for example, via natural language. In this paper, we formulate it as a language conditioned visual content generation problem that is further divided into a floor plan generation and an interior texture (such as floor and wall) synthesis task. The only control signal of the generation process is the linguistic expression given by users that describe the house details. To this end, we propose a House Plan Generative Model (HPGM) that first translates the language input to a structural graph representation and then predicts the layout of rooms with a Graph Conditioned Layout Prediction Network (GC LPN) and generates the interior texture with a Language Conditioned Texture GAN (LCT-GAN). With some post-processing, the final product of this task is a 3D house model. To train and evaluate our model, we build the first Text-to-3D House Model dataset.

cs.CV↗

Enhancing the Three-Photon Luminesce via the Resonance in Lead Halide Perovskite Metasurfaces

Lead halide perovskites (MAPbX3) have emerged as promising materials for photovoltaic and optoelectronic devices. However, their exceptional nonlinear properties have not been fully exploited in nanophotonics yet. Herein we fabricate MAPbX3 perovskite metasurfaces and explore their internal nonlinear processes. While both of third-order harmonic generation (THG) and three-photon luminescence are generated, the latter one is less affected by the material loss and has been significantly enhanced by a factor of 60. The corresponding simulation reveals that the improvement is caused by the resonant enhancement of incident laser in perovskite metasurface. Interestingly, such kind of resonance-enhanced three-photon luminescence holds true for metasurfaces with a small period number of 4, enabling new applications of perovskite metasurface in high-resolution nonlinear color nanoprinting and optical encoding. The encoded information "NANO" is visible only when the incident laser is on-resonance. The off-resonance pumping and the single-photon excitation just produce a uniform dark or photoluminescence background.

physics.app-ph↗

Lead Halide Perovskite based Dynamic Metasurfaces

Lead halide perovskites (MAPbX3) are known to have high refractive index and controllable bandgap, making them attractive for all-dielectric and tunable metasurfaces. Till now, perovskite metasurfaces have only been used in structural colors. More interesting meta-devices with 2π phase control are still absent. Here we experimentally demonstrate the MAPbX3 perovskite based metasurfaces with a complete control of phase shift in a reflection mode. By utilizing MAPbBr3 cut-wires as meta-atoms on a ground metal film, we find that the MAPbBr3 perovskite metasurface can produce full phase control from 0 to 2π and high reflection efficiency simultaneously. Consequently, high-efficiency polarization conversion, anomalous reflection and meta-hologram have been successfully produced. Most interestingly, the bandgap of MAPbX3 perovskite can be post-synthetically and reversibly tuned via anion exchange, providing a new approach to dynamically control of the all-dielectric meta-devices with novel function such as anomalous reflection and hologram et al.

physics.app-ph↗

Ultrafast photocarrier recombination dynamics in black phosphorus-molybdenum disulfide (BP/MoS2) heterostructure

Van der Waals (vdW) heterostructures constructed with two-dimensional (2D) materials have attracted great interests, due to their fascinating properties and potential for novel applications. While earlier efforts have advanced the understanding of the ultrafast cross-layer charge transfer process in 2D heterostructures, mechanisms for the interfacial photocarrier recombination remain, to a large extent, unclear. Here, we investigate a heterostructure comprised of black phosphorus (BP) and molybdenum disulfide (MoS2), with a type-II band alignment. Interestingly, it is found that the photo-generated electrons in MoS2 (transferred from BP) exhibit an ultrafast lifetime of about 5 ps, significantly shorter than those of the constituent materials. By corroborating with the relaxation of photo-excited holes in BP, it is revealed that the ultrafast time constant is as a result of efficient Langevin recombination, where the high hole mobility of BP facilitates a large recombination coefficient (approximately 2x10^-10 m^2/s). In addition, broadband transient absorption spectroscopy confirms that the hot electrons transferred to MoS2 distribute over a broad energy range following an ultrafast thermalization. The rate of the interlayer Langevin recombination is found to exhibit no energy level dependence. Our findings provide essential insights into the fundamental photo-physics in type-II 2D heterostructures, and also provide useful guidelines for customizing photocarrier lifetimes of BP for high-speed photo-sensitive devices.

cond-mat.mes-hall↗

Orientational migration of halide ion in lead halide perovskites

With the rapid evolution of lead halide perovskite solar cells, there are considerable evidences that the mobile ions strongly impact their properties. However, except the activation energy, the other properties of ionic migration are mostly explored with first principle calculations. Here we investigate the migration of halide ion (vacancy) in lead bromide perovskite single crystalline microplates. In contrast to conventional studies with external bias voltages, we introduce built-in potentials into the microplates via low-energy electron beams and study the corresponding ionic migrations. By aligning the potentials along particular crystal planes, the reduction of Pb2+ to Pb0 has been observed at the un-irradiated center of each cell, demonstrating that the migration of halide ion has preferred directions for the first time. Our observations are consistent with the recent theoretical models and shall open up a new route to improve the performances of perovskite solar cells.

cond-mat.mtrl-sci↗

Automatic Structural Scene Digitalization

In this paper, we present an automatic system for the analysis and labeling of structural scenes, floor plan drawings in Computer-aided Design (CAD) format. The proposed system applies a fusion strategy to detect and recognize various components of CAD floor plans, such as walls, doors, windows and other ambiguous assets. Technically, a general rule-based filter parsing method is fist adopted to extract effective information from the original floor plan. Then, an image-processing based recovery method is employed to correct information extracted in the first step. Our proposed method is fully automatic and real-time. Such analysis system provides high accuracy and is also evaluated on a public website that, on average, archives more than ten thousands effective uses per day and reaches a relatively high satisfaction rate.

cs.GR↗

Reflectance dependence of polytetrafluoroethylene on thickness for xenon scintillation light

Many rare event searches including dark matter direct detection and neutrinoless double beta decay experiments take advantage of the high VUV reflective surfaces made from polytetrafluoroethylene (PTFE) reflector materials to achieve high light collection efficiency in their detectors. As the detectors have grown in size over the past decade, there has also been an increased need for ever thinner detector walls without significant loss in reflectance to reduce dead volumes around active noble liquids, outgassing, and potential backgrounds. We report on the experimental results to measure the dependence of the reflectance on thickness of two PTFE samples at wavelengths near 178 nm. No change in reflectance was observed as the thickness of a cylindrically shaped PTFE vessel immersed in liquid xenon was varied between 1 mm and 9.5 mm.

physics.ins-det↗