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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Towards Storage of Sub-Megahertz Single Photons in Gradient Echo Memory
摘要： Quantum repeaters are foundational to establishing the long distance quantum communication channels necessary to create a global communication network. A quantum memory capable of storing optical quantum states is an integral component of the quantum repeater. A wide variety of mechanisms for implementing an optical quantum memory have been investigated, ranging from simple optical delay lines to complicated photon echo schemes. The scheme of interest here is the gradient echo memory (GEM). GEM has been demonstrated to be one of the most efficient memory schemes to date, with up to 87% recall efficiency and up to 1ms coherence time when performed in a cold atomic ensemble of 87Rb atoms. Until now, GEM has only been investigated with weak coherent pulses as no single photon source met the demanding spectral requirements of the memory protocol. In particular, it requires sub-megahertz linewidth photons at the atomic transitions of 87Rb. A compatible source has been developed utilising cavity-enhanced spontaneous parametric downconversion (SPDC) generating photons with a bandwidth of 429 ± 10 kHz. This is, to our knowledge, the narrowest single photon bandwidth from SPDC to date. Integration with this source enables single photon storage for the first time using GEM and allows for its single photon level characteristics to finally be investigated. Single-photon quantum memory opens up the prospect of using the system as a quantum optical gate. Storing multiple single photon states simultaneously in the quantum memory can potentially give rise to photon-photon interactions due to cross phase modulation.
关键词： single photon source,gradient echo memory,quantum repeaters,sub-megahertz linewidth photons,quantum memory
更新于2025-09-11 14:15:04
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Acceptor Gradient Polymer Donors for Non-Fullerene Organic Solar Cells
摘要： In organic solar cells, maximizing the open-circuit voltage (VOC) via minimization of the ionization energy or electron a?nity o?sets of the blended donor and acceptor often comes at the expense of achieving a considerable amount of short-circuit current (JSC). To explore a hypothesis for the design of materials that may circumvent this tradeo?, eight structurally similar polymers were synthesized consisting of a ?uorinated/non-?uorinated benzothiadiazole (BTDF/BTD) strong acceptor moiety, a thiophene ester (TE) weak acceptor, and various donor units composed of bithiophene (T2), biEDOT, and benzodithiophene (BDT) to form six acceptor gradient and two nongradient polymers. The acceptor gradient motif was designed and theorized to induce more facile exciton dissociation in low driving force solar cells by creating a further separated intramolecular charge-transfer state between the strong BTD acceptor and various donor units through a bridging TE component. Solar cells were fabricated using the eight polymers blended with phenyl-C71-butyric-acid methyl ester (PC71BM) to reveal two top performing isomeric polymers, T2-BTDF-(TE2) and TE2-BTDF-(T2), which were further tested with several non-fullerene acceptors (NFAs): EH-IDTBR, ITIC, and ITIC-4F. In order to fabricate optimally performing solar cells, a 0.2 eV ionization energy o?set was found to be essential or the short-circuit current of the NFA cells diminished dramatically. Ultimately, optimized NFA solar cells were fabricated using ITIC-4F paired with each of the top performing polymers to produce an average PCE of 7.3% for TE2-BTDF-(T2) (nongradient) and 3.6% for T2-BTDF-(TE2) (gradient). The acceptor gradient e?ect was not shown to reduce the amount of charge recombination in NFA solar cells mainly due to the inability to fabricate solar cells, with minimal ionization energy or electron a?nity o?sets along with morphological complications. This work stresses the importance of acquiring accurate ionization energies and electron a?nities when characterizing solar cell energetics, as di?erences as small as 0.1 eV in the o?sets can make a signi?cant impact on overall charge collection.
关键词： acceptor gradient polymers,open-circuit voltage,electron affinity offset,charge recombination,organic solar cells,non-fullerene acceptors,ionization energy offset,short-circuit current
更新于2025-09-11 14:15:04
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[IEEE 2019 Chinese Control And Decision Conference (CCDC) - Nanchang, China (2019.6.3-2019.6.5)] 2019 Chinese Control And Decision Conference (CCDC) - A Photovoltaic MPPT Control Strategy Based on Gradient Optimization and MPP Voltage Law
摘要： In this work, a maximum power point tracking (MPPT) control algorithm is developed to determine power efficiency, and to improve the transient nature of the power curve characteristics of a PV cell. Based on the analysis of existing MPPT methods, for PV systems, the relationship between MPP voltage and the open circuit voltage of PV cell under different conditions is studied; moreover, a novel MPPT control strategy which can be applied to different irradiance conditions based on a sub-domain gradient optimization principle and MPP voltage law is proposed. Simulation results show that the proposed method has advantages of fast dynamic response and a non-oscillatory steady state response under different irradiance conditions and input waveforms. For the experimental setup, an existing control method and the proposed MPPT control algorithm are implemented on solar PV cell; it was observed that the proposed MPPT algorithm has stable steady state dynamic characteristics and a fast response speed.
关键词： MPPT,photovoltaic system,voltage law,gradient optimization
更新于2025-09-11 14:15:04
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Static bending and free vibration of organic solar cell resting on Winkler-Pasternak elastic foundation through the modified strain gradient theory
摘要： Organic solar cell (OSC), which is deemed to be the most promising third generation solar energy application, is developing vigorously. Based on the modified strain gradient theory (MSGT) and the refined shear deformation plate theory, static bending and free vibration of the size-dependent OSC are thoroughly investigated in this paper. A Winkler-Pasternak elastic foundation is considered for the OSC. A multiscale suitable plate analysis framework (i.e., both macro- and micro plates can be handled) is developed herein. Three length scale parameters are incorporated in the presented analysis to capture the size-dependency of the OSC. By setting two or three of them into zero, the presented model could degenerate into the modified couple stress theory (MCST) and the classical plate theory (CPT). The derivation of the governing equations and the corresponding boundary conditions are conducted by Hamilton principle. The Navier-type solution is employed for solving the governing equations of the simply supported OSC. The accuracy of the presented method is validated. Extensive numerical experiments have been conducted to investigate the differences between the adopted MSGT, the MCST and the CPT. Moreover, the impacts of the geometrical configuration as well as the elastic foundation parameters on the static bending and free vibration characteristics are illustrated in the numerical studies. This paper also explores the thickness of the active layer effect on the free vibration behaviour in combination with the power conversion efficiency (PCE) of the OSC.
关键词： Structural analysis,Modified strain gradient theory,Organic solar cell
更新于2025-09-11 14:15:04
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High Sensitivity Detection of Copper Ions in Oysters Based on the Fluorescence Property of Cadmium Selenide Quantum Dots
摘要： Enhancing the mass transport from the flow field side to the membrane side without sacrificing the active surface area is a critical strategy for the design of electrodes in flow-field structured vanadium redox flow batteries (VRFBs). In this work, we design and prepare a novel porous electrode with a gradient distribution in pores, enabling a gradual decrease in permeability but an increase in active surface areas from the flow field side to the membrane side. This design not only increases the electrode utilization due to the enhanced mass transport near the flow field side, but also avoids the loss of active surface area near the membrane side. Numerical modeling results show that compared to the conventional electrode design, the gradient electrode design can promote the uniform distribution of local reaction current density and overpotential, leading to a lower charge voltage and higher discharge voltage. Experimental results show that at the current density of 240 mA cm?2, the battery with the gradient electrode design delivers a 69% higher discharge capacity than that with the conventional electrode design, demonstrating the superiority of the gradient electrode design strategy.
关键词： Gradient porous electrode,Large-scale energy storage,Mass transport,Vanadium redox flow batteries
更新于2025-09-11 14:15:04
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Effects of end-on oriented polymer chains at the donor/acceptor interface in organic solar cells
摘要： The transport and magnetic properties of LaAlO3/SrTiO3 (LAO/STO) heterostructure have been studied during cooling and warming. The strain gradient perpendicular to the surface of the heterostructure increases with the thickness of LAO film. The conductivity accelerated recoveries (CAR) are found at 80 K and 176 K in the interface of LAO/STO sample with millimeter scale, and are more obvious for thicker LAO layers during warming. These two recovering temperatures correspond to the migrating energies of oxygen single vacancy and divacancy trapped by polarized domain walls, separately. This indicated that domain walls diffuse along the longitudinal direction and expand to larger area due the strain gradient perpendicular to the interface. The stable and precise accelerating recovering temperatures make the sample at a larger scale a potential widely applied temperature standard reference. The magnetization measurements reveal the coexistence of paramagnetic and diamagnetic in the LAO/STO samples at whole temperature from 2 K to 300 K. The abnormal electric resistance rise is observed with the decreasing temperature below 25 K for the samples of 7 and 15 LAO layers. This anomaly is attributed to the Kondo effect below 25 K and weak anti-localization below 5 K due to the weightier paramagnetic content. The larger diamagnetic content suppresses these contributions in 25 LAO layers sample. This work provided an insightful view that the strain modified structure domain leads to the enhancement of CAR effect, which helps to achieve a better understanding of domain related physics in the LAO/STO system.
关键词： magnetization,LaAlO3/SrTiO3 heterostructure,conductivity accelerated recoveries,domain walls,weak anti-localization,strain gradient,Kondo effect
更新于2025-09-11 14:15:04
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7.4: Metal Halide Perovskite Nanophosphors for Micro‐LEDs
摘要： 1. Changes in precipitation have the potential to cause dramatic changes in ecosystem carbon (C) cycling; however, it remains unclear whether different components of the net ecosystem exchange (NEE) (e.g., C uptake vs. release, plant vs. microbe respiration, above-ground vs. below-ground plant respiration) have similar or differential sensitivity to precipitation gradients. 2. We conducted a manipulative field experiment (from 2015 to 2017) with six precipitation treatments, including 1/12 annual precipitation (P), 1/4 P, 1/2 P, 3/4 P, P and 5/4 P in an alpine meadow to investigate the responses of the NEE components. 3. Over the 3 years, all C fluxes showed a nonlinear response to the precipitation gradients, except for root respiration. The most extreme drought treatment (1/12 P) caused strong reductions in NEE by 15.57%, gross primary productivity by 17.26% and ecosystem respiration by 19.05%, in contrast to the control. Plant respiration was more sensitive to precipitation change than microbe respiration, and above-ground plant respiration was more susceptible than below-ground respiration. Structural equation models revealed that the response of C fluxes under precipitation changes was primarily due to changes in the soil water content and above-ground net primary productivity. 4. Our findings indicate that future precipitation changes, particularly extreme drought, will decrease ecosystem C fluxes with different magnitudes, leading to a consequent reduction of NEE. These emergent ecosystem properties are essential for the improved elucidation of carbon cycle dynamics and benchmarking models, to predict ecosystem responses to precipitation changes.
关键词： carbon fluxes,manipulative experiment,precipitation gradient,climate extremes,alpine meadow,nonlinear response
更新于2025-09-11 14:15:04
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Thermo-Mechanical Analysis of Laser Additive Manufacturing for Metals
摘要： The aim of this study is to develop a finite element analysis technique to characterize the distributions of temperature and stress in the process of multilayer deposition of metallic powders by laser additive manufacturing (LAM). Simulation results indicate the residual normal stress in the laser moving direction is greater than that in other directions due to a larger temperature gradient, and it increases with number of deposited layers. Highly residual stresses are present in the LAM build and at the base nearby the interface between the build and base.
关键词： laser additive manufacturing,temperature gradient,finite element analysis,metal,residual stress
更新于2025-09-11 14:15:04
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Coarse-to-Fine Extraction of Small-Scale Lunar Impact Craters From the CCD Images of the Chang'E Lunar Orbiters
摘要： Lunar impact craters form the basis for lunar geological stratigraphy, and small-scale craters further enrich the basic statistical data for the estimation of local geological ages. Thus, the extraction of lunar impact craters is an important branch of modern planetary studies. However, few studies have reported on the extraction of small-scale craters. Therefore, this paper proposes a coarse-to-fine resolution method to automatically extract small-scale impact craters from charge-coupled device (CCD) images using histogram of oriented gradient (HOG) features and a support vector machine (SVM) classifier. First, large-scale craters are extracted as samples from the Chang'E-1 images with spatial resolutions of 120 m. The SVM classifier is then employed to establish the criteria for classifying craters and noncraters from the HOG features of the extracted samples. The criteria are then used to extract small-scale craters from higher resolution Chang'E-2 CCD images with spatial resolutions of 1.4, 7, and 50 m. The sample database is updated with the newly extracted small-scale craters for the purpose of the progressive optimization of the extraction. The proposed method is tested on both simulated images and multiple resolutions of real CCD images acquired by the Chang'E orbiters and provides high accuracy results in the extraction of the small-scale impact craters, the smallest of which is 20 m.
关键词： small-scale impact craters,Chang'E satellites,charge-coupled device (CCD) images,support vector machine (SVM) classifier,histogram of oriented gradient (HOG) feature
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE 3rd International Conference on Image, Vision and Computing (ICIVC) - Chongqing (2018.6.27-2018.6.29)] 2018 IEEE 3rd International Conference on Image, Vision and Computing (ICIVC) - Surface Defect Detection Based on Gradient LBP
摘要： The LBP histogram obtained based on the local binary pattern (LBP) method usually has a higher dimension, and not conducive to calculation. The LBP method adopts the gray difference value between single points as the LBP output value, which is not robust to noise and illumination. Therefore, this paper improves the traditional LBP method and proposes a surface defect detection method based on gradient local binary pattern (GLBP), which uses image sub-blocks to reduce the dimensionality of the LBP data matrix. The method adopts weighted binary output values in eight directions within the neighborhood to indicate local gray changes, which suppresses the effects of light and noise on the detection results. Experiments show that the method can determine the defect location well and provide good feature information for subsequent defect classification.
关键词： surface defect detection,gradient LBP,LBP,image sub-block division,LBP dimension reduction
更新于2025-09-10 09:29:36