Forward Vehicle Collision Warning Based on Quick Camera Calibration

Forward Vehicle Collision Warning (FCW) is one of the most important functions for autonomous vehicles. In this procedure, vehicle detection and distance measurement are core components, requiring accurate localization and estimation. In this paper, we propose a simple but efficient forward vehicle collision warning framework by aggregating monocular distance measurement and precise vehicle detection. In order to obtain forward vehicle distance, a quick camera calibration method which only needs three physical points to calibrate related camera parameters is utilized. As for the forward vehicle detection, a multi-scale detection algorithm that regards the result of calibration as distance priori is proposed to improve the precision. Intensive experiments are conducted in our established real scene dataset and the results have demonstrated the effectiveness of the proposed framework

Exceptional cavity quantum electrodynamics

An open quantum system operated at the spectral singularities where dimensionality reduces, known as exceptional points (EPs), demonstrates distinguishing behavior from the Hermitian counterpart. Based on the recently proposed microcavity with exceptional surface (ES), we report and explain the peculiar quantum dynamics in atom-photon interaction associated with EPs: cavity transparency, decoherence suppression beyond the limitation of Jaynes-Cummings (JC) system, and the population trapping of lossy cavity. An analytical description of the local density of states (LDOS) for ES microcavity is derived from an equivalent cavity quantum electrodynamics (QED) model, which goes beyond the single-excitation approximation and allows exploring the quantum effects of EPs on multiphoton process by parametrizing the extended cascaded quantum master equation. It reveals that a square Lorentzian term in LDOS induced by second-order EPs interferes with the linear Lorentzian profile, giving rise to cavity transparency for atom with special transition frequency in the weak coupling regime. This additional contribution from EPs also breaks the limit on dissipation rate of JC system bounded by bare components, resulting in the decoherence suppression with anomalously small decay rate of the Rabi oscillation and the long-time dynamics. Remarkably, we find that the cavity population can be partially trapped at EPs, achieved by forming a bound dressed state in the limiting case of vanishing atom decay. Our work unveils the exotic phenomena unique to EPs in cavity QED systems, which opens the door for controlling light-matter interaction at the quantum level through non-Hermiticity, and holds great potential in building high-performance quantum-optics devices.Comment: 11 pages, 6 figure

Dressed bound states at chiral exceptional points

Atom-photon dressed states are a basic concept of quantum optics. Here, we demonstrate that the non-Hermiticity of open cavity can be harnessed to form the dressed bound states (DBS) and identify two types of DBS, the vacancy-like DBS and Friedrich-Wintgen DBS, in a microring resonator operating at a chiral exceptional point. With the analytical DBS conditions, we show that the vacancy-like DBS occurs when an atom couples to the standing wave mode that is a node of photonic wave function, and thus is immune to the cavity dissipation and characterized by the null spectral density at cavity resonance. While the Friedrich-Wintgen DBS can be accessed by continuously tuning the system parameters, such as the atom-photon detuning, and evidenced by a vanishing Rabi peak in emission spectrum, an unusual feature in the strong-coupling anticrossing. We also demonstrate the quantum-optics applications of the proposed DBS. Our work exhibits the quantum states control through non-Hermiticity of open quantum system and presents a clear physical picture on DBS at chiral exceptional points, which holds great potential in building high-performance quantum devices for sensing, photon storage, and nonclassical light generation.Comment: 13 pages, 5 figure

Enhanced coherent light-matter interaction and room-temperature quantum yield of plasmonic resonances engineered by a chiral exceptional point

Strong dissipation of plasmonic resonances is detrimental to quantum manipulation. To enhance the quantum coherence, we propose to tailor the local density of states (LDOS) of plasmonic resonances by integrating with a photonic cavity operating at a chiral exceptional point (CEP), where the phase of light field can offer a new degree of freedom to flexibly manipulate the quantum states. A quantized few-mode theory is employed to reveal that the LDOS of the proposed hybrid cavity can evolve into sub-Lorentzian lineshape, with order-of-magnitude linewidth narrowing and additionally a maximum of eightfold enhancement compared to the usual plasmonic-photonic cavity without CEP. This results in the enhanced coherent light-matter interaction accompanied by the reduced dissipation of polaritonic states. Furthermore, a scattering theory based on eigenmode decomposition is present to elucidate two mechanisms responsible for the significant improvement of quantum yield at CEP, the reduction of plasmonic absorption by the Fano interference and the enhancement of cavity radiation through the superscattering. Importantly, we find the latter allows achieving a near-unity quantum yield at room temperature; in return, high quantum yield is beneficial to experimentally verify the enhanced LDOS at CEP by measuring the fluorescence lifetime of a quantum emitter. Therefore, our work demonstrates that the plasmonic resonances in CEP-engineered environment can serve as a promising platform for exploring the quantum states control by virtue of the non-Hermiticity of open optical resonators and building the high-performance quantum devices for sensing, spectroscopy, quantum information processing and quantum computing.Comment: 20 pages,9 figure

Application of flame image velocimetry for flame front growth and turbulence analysis in an optical direct-injection spark-ignition engine

High-speed flame imaging has been widely used to investigate flame propagation in optically accessible direct-injection spark-ignition (DISI) engines. This study proposes flame image velocimetry (FIV), a new diagnostic method enabling time-resolved, two-dimensional flame front vector extraction and turbulence intensity calculation. A Matlab-based open-source code is used for this flame front FIV analysis, and the systematic optimisation of processing parameters is performed. The Reynolds decomposition based on a spatial filtering method is applied to derive turbulence intensity. The new FIV method is first applied to two injectors with different nozzle structures. The results show that a smaller hole diameter and counterbore hole shape leads to higher flame front vector magnitude, higher turbulence intensity and more uniform distribution of turbulence than the injector with a larger hole diameter and cylindrical hole shape. This FIV result explains higher engine power output and lower cyclic variations measured for the smaller hole injector. Injection pressure in the range of 5~25 MPa is also tested for FIV measurements. Mie-scattering images confirm better air/fuel mixing for increased injection pressure; however, the in-cylinder pressure and power output do not continue to increase with an increase in injection pressure. It is observed they peak at 15 MPa and decrease at higher injection pressure, corresponding to the trends of flame front vector magnitude and turbulence intensity. The distribution of turbulence intensity along the flame boundary shows increased variations at injection pressure higher than 15 MPa, because local over-mixing caused low turbulent flame growth regions. Nevertheless, 25 MPa has much lower soot luminosity than that of 15 MPa, explaining the development trend towards higher injection pressure. Another parameter of interest is equivalence ratio. The flame front FIV analysis shows that excess air leads to slower flame front growth and lower turbulence intensity. At its lean limit, significant spatial variations are measured in both the flame front vector magnitude and turbulence intensity. The results suggest new engine design for higher turbulence generation is required to extend the lean limit and thus higher fuel economy is achieved in a DISI engine

Optical localization and polarization microscopy with angstrom precision based on position-ultra-sensitive giant Lamb shift

We propose an optical localization and polarization microscopy scheme with sub-nanometer precision for an emitter (atom/molecule/quantum dot) based on its Lamb shift. It is revealed that the position-ultra-sensitive giant Lamb shift with three or more orders of magnitude larger than that in the free space, can be induced by higher-order plasmonic dark modes of a metal nanoparticle. More importantly, this giant Lamb shift can be ultra-sensitively observed from the optical scattering spectrum of the nanoparticle via scanning an emitter by a sub-nanometer step, and the orientation of the Lamb shift image can be utilized to identify the dipole polarization of the emitter. They enable the optical spectrum microscope technology with angstrom precision and polarization identification, which will bring about broad applications in many fields, such as physics, chemistry, medicine, life science and materials science

High-throughput and separating-free phenotyping method for on-panicle rice grains based on deep learning

Rice is a vital food crop that feeds most of the global population. Cultivating high-yielding and superior-quality rice varieties has always been a critical research direction. Rice grain-related traits can be used as crucial phenotypic evidence to assess yield potential and quality. However, the analysis of rice grain traits is still mainly based on manual counting or various seed evaluation devices, which incur high costs in time and money. This study proposed a high-precision phenotyping method for rice panicles based on visible light scanning imaging and deep learning technology, which can achieve high-throughput extraction of critical traits of rice panicles without separating and threshing rice panicles. The imaging of rice panicles was realized through visible light scanning. The grains were detected and segmented using the Faster R-CNN-based model, and an improved Pix2Pix model cascaded with it was used to compensate for the information loss caused by the natural occlusion between the rice grains. An image processing pipeline was designed to calculate fifteen phenotypic traits of the on-panicle rice grains. Eight varieties of rice were used to verify the reliability of this method. The R2 values between the extraction by the method and manual measurements of the grain number, grain length, grain width, grain length/width ratio and grain perimeter were 0.99, 0.96, 0.83, 0.90 and 0.84, respectively. Their mean absolute percentage error (MAPE) values were 1.65%, 7.15%, 5.76%, 9.13% and 6.51%. The average imaging time of each rice panicle was about 60 seconds, and the total time of data processing and phenotyping traits extraction was less than 10 seconds. By randomly selecting one thousand grains from each of the eight varieties and analyzing traits, it was found that there were certain differences between varieties in the number distribution of thousand-grain length, thousand-grain width, and thousand-grain length/width ratio. The results show that this method is suitable for high-throughput, non-destructive, and high-precision extraction of on-panicle grains traits without separating. Low cost and robust performance make it easy to popularize. The research results will provide new ideas and methods for extracting panicle traits of rice and other crops

Topologically protected subradiant cavity polaritons through linewidth narrowing enabled by dissipationless edge states

Cavity polaritons derived from the strong light-matter interaction at the quantum level provide a basis for efficient manipulation of quantum states via cavity field. Polaritons with narrow linewidth and long lifetime are appealing in applications such as quantum sensing and storage. Here, we propose a prototypical arrangement to implement a whispering-gallery-mode resonator with topological mirror moulded by one-dimensional atom array, which allows to boost the lifetime of cavity polaritons over an order of magnitude. This considerable enhancement attributes to the coupling of polaritonic states to dissipationless edge states protected by the topological bandgap of atom array that suppresses the leakage of cavity modes. When exceeding the width of Rabi splitting, topological bandgap can further reduce the dissipation from polaritonic states to bulk states of atom array, giving arise to subradiant cavity polaritons with extremely sharp linewidth. The resultant Rabi oscillation decays with a rate even below the free-space decay of a single quantum emitter. Inheriting from the topologically protected properties of edge states, the subradiance of cavity polaritons can be preserved in the disordered atom mirror with moderate perturbations involving the atomic frequency, interaction strengths and location. Our work opens up a new paradigm of topology-engineered quantum states with robust quantum coherence for future applications in quantum computing and network.Comment: 19 pages,8 figure

Quantum Hydrodynamic Model by Moment Closure of Wigner Equation

In this paper, we derive the quantum hydrodynamics models based on the moment closure of the Wigner equation. The moment expansion adopted is of the Grad type firstly proposed in \cite{Grad}. The Grad's moment method was originally developed for the Boltzmann equation. In \cite{Fan_new}, a regularization method for the Grad's moment system of the Boltzmann equation was proposed to achieve the globally hyperbolicity so that the local well-posedness of the moment system is attained. With the moment expansion of the Wigner function, the drift term in the Wigner equation has exactly the same moment representation as in the Boltzmann equation, thus the regularization in \cite{Fan_new} applies. The moment expansion of the nonlocal Wigner potential term in the Wigner equation is turned to be a linear source term, which can only induce very mild growth of the solution. As the result, the local well-posedness of the regularized moment system for the Wigner equation remains as for the Boltzmann equation