Nonparaxiality-triggered Landau-Zener transition in topological photonic waveguides

Photonic lattices have been widely used for simulating quantum physics, owing to the similar evolutions of paraxial waves and quantum particles. However, nonparaxial wave propagations in photonic lattices break the paradigm of the quantum-optical analogy. Here, we reveal that nonparaxiality exerts stretched and compressed forces on the energy spectrum in the celebrated Aubry-Andre-Harper model. By exploring the mini-gaps induced by the finite size of the different effects of nonparaxiality, we experimentally present that the expansion of one band gap supports the adiabatic transfer of boundary states while Landau-Zener transition occurs at the narrowing of the other gap, whereas identical transport behaviors are expected for the two gaps under paraxial approximation. Our results not only serve as a foundation of future studies of dynamic state transfer but also inspire applications leveraging nonparaxial transitions as a new degree of freedom.Comment: 17 pages, 4 figure

Significant contrasts in aerosol acidity between China and the United States

Aerosol acidity governs several key processes in aerosol physics and chemistry, thus affecting aerosol mass and composition and ultimately climate and human health. Previous studies have reported aerosol pH values separately in China and the United States (USA), implying different aerosol acidity between these two countries. However, there is debate about whether mass concentration or chemical composition is the more important driver of differences in aerosol acidity. A full picture of the pH difference and the underlying mechanisms responsible is hindered by the scarcity of simultaneous measurements of particle composition and gaseous species, especially in China. Here we conduct a comprehensive assessment of aerosol acidity in China and the USA using extended ground-level measurements and regional chemical transport model simulations. We show that aerosols in China are significantly less acidic than in the USA, with pH values 1&ndash;2&nbsp;units higher. Based on a proposed multivariable Taylor series method and a series of sensitivity tests, we identify major factors leading to the pH difference. Compared to the USA, China has much higher aerosol mass concentrations (gas + particle, by a factor of 8.4 on average) and a higher fraction of total ammonia (gas + particle) in the aerosol composition. Our assessment shows that the differences in mass concentrations and chemical composition play equally important roles in driving the aerosol pH difference between China and the USA &ndash; increasing the aerosol mass concentrations (by a factor of 8.4) but keeping the relative component contributions the same in the USA as the level in China increases the aerosol pH by &sim;&thinsp;1.0&nbsp;units and further shifting the chemical composition from US conditions to China's that are richer in ammonia increases the aerosol pH by &sim;&thinsp;0.9 units. Therefore, China being both more polluted than the USA and richer in ammonia explains the aerosol pH difference. The difference in aerosol acidity highlighted in the present study implies potential differences in formation mechanisms, physicochemical properties, and toxicity of aerosol particles in these two countries. &nbsp;</p

Spatial Distribution of Ozone Formation in China Derived from Emissions of Speciated Volatile Organic Compounds

Ozone (O₃) pollution is becoming increasingly severe in China. In addition, our limited understanding of the relationship between O₃ and volatile organic compounds (VOCs), is an obstacle to improving air quality. By developing an improved source-oriented speciated VOC emission inventory in 2013, we estimated the ozone formation potential (OFP) and investigated its characteristics in China. Besides, a comparison was made between our estimates and space-based observations from the ozone monitoring instrument (OMI) on the National Aeronautics and Space Administration (NASA)’s Aura satellite. According to our estimates, <i>m-/p</i>-xylene, ethylene, formaldehyde, toluene, and propene were the five species that had the largest potential to form ozone, and on-road vehicles, industrial processes, biofuel combustion, and surface coating were the key contributing sectors. Among different regions of China, the North China Plain, Yangtze River Delta, and Pearl River Delta had the highest OFP values. Our results suggest that O₃ formation is VOC-limited in major urban areas of China. Additionally, considering the different photochemical reactivities of various VOC species and the disparate energy and industry structures in the different regions of China, more efficient OFP-based and localized VOC control measures should be implemented, instead of the current mass-based and nationally uniform policies

Spatial Distribution of Ozone Formation in China Derived from Emissions of Speciated Volatile Organic Compounds

Ozone (O₃) pollution is becoming increasingly severe in China. In addition, our limited understanding of the relationship between O₃ and volatile organic compounds (VOCs), is an obstacle to improving air quality. By developing an improved source-oriented speciated VOC emission inventory in 2013, we estimated the ozone formation potential (OFP) and investigated its characteristics in China. Besides, a comparison was made between our estimates and space-based observations from the ozone monitoring instrument (OMI) on the National Aeronautics and Space Administration (NASA)’s Aura satellite. According to our estimates, <i>m-/p</i>-xylene, ethylene, formaldehyde, toluene, and propene were the five species that had the largest potential to form ozone, and on-road vehicles, industrial processes, biofuel combustion, and surface coating were the key contributing sectors. Among different regions of China, the North China Plain, Yangtze River Delta, and Pearl River Delta had the highest OFP values. Our results suggest that O₃ formation is VOC-limited in major urban areas of China. Additionally, considering the different photochemical reactivities of various VOC species and the disparate energy and industry structures in the different regions of China, more efficient OFP-based and localized VOC control measures should be implemented, instead of the current mass-based and nationally uniform policies

Spatial Distribution of Secondary Organic Aerosol Formation Potential in China Derived from Speciated Anthropogenic Volatile Organic Compound Emissions

Fine particulate matter (PM_2.5), largely composed of secondary organic aerosol (SOA), is currently one of the most intractable environmental problems in China. As crucial precursors for SOA, understanding the formation propensity of various volatile organic compound (VOC) species and sources is useful for pollution control. In this work, we estimated the SOA formation potential (SOAP) of anthropogenic VOC emissions based on an improved speciated VOC emission inventory and investigated its distribution in China. According to our estimates, toluene had the largest SOAP, followed by <i>n-</i>dodecane, <i>m-/p-</i>xylene, styrene, <i>n-</i>decane, and <i>n-</i>undecane, while passenger cars, chemical fiber manufacturing, asphalt paving, and building coating were the top five SOAP-contributing sources nationwide. The spatial distribution of SOAP in China shows a distinct pattern of high values in the southeast and low values in the northwest. Beijing–Tianjin–Hebei and surroundings, the Yangtze River Delta, Pearl River Delta, and Sichuan–Chongqing District were found to have the highest SOAP, particularly in urban areas. The major SOAP-contributing species and sources differed among these regions, which was attributed to local industrial and energy structures. Our results suggest that to mitigate PM_2.5 pollution in China, more efficient SOAP-based control measures should be implemented instead of current emissions-based policies, and VOC control strategies should be adapted to local conditions

Using CNN with Multi-Level Information Fusion for Image Denoising

Deep convolutional neural networks (CNN) with hierarchical architectures have obtained good results for image denoising. However, in some cases where the noise level is unknown and the image background is complex, it is challenging to obtain robust information through CNN. In this paper, we present a multi-level information fusion CNN (MLIFCNN) in image denoising containing a fine information extraction block (FIEB), a multi-level information interaction block (MIIB), a coarse information refinement block (CIRB), and a reconstruction block (RB). In order to adapt to more complex image backgrounds, FIEB uses parallel group convolution to extract wide-channel information. To enhance the robustness of the obtained information, a MIIB uses residual operations to act in two sub-networks for implementing the interaction of wide and deep information to adapt to the distribution of different noise levels. To enhance the stability of the training denoiser, CIRB stacks common and group convolutions to refine the obtained information. Finally, RB uses a residual operation to act in a single convolution in order to obtain the resultant clean image. Experimental results show that our method is better than many other excellent methods, both in terms of quantitative and qualitative aspects

Experimental Investigation on the Vertical Structure Characteristics of Internal Solitary Waves

An experimental investigation of the vertical structure characteristics of internal solitary waves (ISWs) was systematically carried out in a large gravitationally stratified fluid flume. Four different stratifications were established, and basic elements of ISWs were measured by a conductivity probe array. The vertical distributions of the amplitude, characteristic frequency and waveform of two types of ISWs under different stratifications were obtained, and the experimental results were compared with the theoretical model. The study shows that most vertical structures of the amplitude under different stratifications agree with those of the theoretical model, while there are some deviations for ISWs with large amplitudes. Neither the two-layer model nor the continuously stratified model can effectively describe the variation in the characteristic frequency at different depths with amplitude. For a single small-amplitude ISW, the characteristic frequency first increases and then decreases with increasing depth. The characteristic frequency is largest at the depth of the maximum buoyancy frequency. For an ISW with a relatively large amplitude, there is likely to be a local minimum of the characteristic frequency near the depth where the maximum buoyancy frequency lies. In different stratifications, the sech2 function of KdV theory can describe the waveforms of ISWs at different depths well

Extraction of high-accuracy control points using ICESat-2 ATL03 in urban areas

The ice, cloud, and land elevation satellite-2 (ICESat-2) can effectively measure global surface elevations and be used as a new data source for global elevation control. ICESat-2 has provided surface-specific data products on land/vegetation (ATL08), ice sheet (ATL06), inland water (ATL13), etc., but not on urban areas. The current research using ICESat-2 data to extract control points mostly based on products already provided, focusing on land, forest and other areas. Few studies have analyzed the feasibility of extracting control points in urban areas, as well as the position and elevation accuracy of control points. In this paper, we proposed a method for extracting high-accuracy control points from ATL03 in urban areas and evaluated the elevation and plane accuracy. First, building and ground photons were extracted and classified according to the photon shape features and neighborhood relationships, thereby addressing the insufficiency of ICESat-2 of not classifying photons in urban areas. Then, high-accuracy photons were selected from the ground photons as the laser control points considering the influence of land cover. Finally, the solid and undulating city outline was used for shape matching with DSM, thereby addressing the problem of plane accuracy evaluation in flat areas. We verified our method in two areas (Nanjing and Auckland) and showed that the method can adequately classify buildings and ground photons in different scenarios. The plane accuracy was better than 3.8 m, which lies well within ICESat-2′s mission requirement, with an elevation accuracy of better than 0.5 m, which meets the accuracy requirements of large-scale mapping, suggesting that photons in urban areas can also provide high-accuracy control data for stereo mapping

Micro-Structure and Thermomechanical Properties of Crosslinked Epoxy Composite Modified by Nano-SiO2: A Molecular Dynamics Simulation

Establishing the relationship among the composition, structure and property of the associated materials at the molecular level is of great significance to the rational design of high-performance electrical insulating Epoxy Resin (EP) and its composites. In this paper, the molecular models of pure Diglycidyl Ether of Bisphenol A resin/Methyltetrahydrophthalic Anhydride (DGEBA/MTHPA) and their nanocomposites containing nano-SiO2 with different particle sizes were constructed. The effects of nano-SiO2 dopants and the crosslinked structure on the micro-structure and thermomechanical properties were investigated using molecular dynamics simulations. The results show that the increase of crosslinking density enhances the thermal and mechanical properties of pure EP and EP nanocomposites. In addition, doping nano-SiO2 particles into EP can effectively improve the properties, as well, and the effectiveness is closely related to the particle size of nano-SiO2. Moreover, the results indicate that the glass transition temperature (Tg) value increases with the decreasing particle size. Compared with pure EP, the Tg value of the 6.5 &Aring; composite model increases by 6.68%. On the contrary, the variation of the Coefficient of Thermal Expansion (CTE) in the glassy state demonstrates the opposite trend compared with Tg. The CTE of the 10 &Aring; composite model is the lowest, which is 7.70% less than that of pure EP. The mechanical properties first increase and then decrease with the decreasing particle size. Both the Young&rsquo;s modulus and shear modulus reach the maximum value at 7.6 &Aring;, with noticeable increases by 12.60% and 8.72%, respectively compared to the pure EP. In addition, the thermal and mechanical properties are closely related to the Fraction of Free Volume (FFV) and Mean Squared Displacement (MSD). The crosslinking process and the nano-SiO2 doping reduce the FFV and MSD value in the model, resulting in better thermal and mechanical properties