Stark Effects of Rydberg Excitons in a Monolayer WSe2 P-N Junction.

The enhanced Coulomb interaction in two-dimensional semiconductors leads to tightly bound electron-hole pairs known as excitons. The large binding energy of excitons enables the formation of Rydberg excitons with high principal quantum numbers (n), analogous to Rydberg atoms. Rydberg excitons possess strong interactions among themselves as well as sensitive responses to external stimuli. Here, we probe Rydberg exciton resonances through photocurrent spectroscopy in a monolayer WSe2 p-n junction formed by a split-gate geometry. We show that an external in-plane electric field not only induces a large Stark shift of Rydberg excitons up to quantum principal number 3 but also mixes different orbitals and brightens otherwise dark states such as 3p and 3d. Our study provides an exciting platform for engineering Rydberg excitons for new quantum states and quantum sensing.

In-Plane Zeeman-Field-Induced Majorana Corner and Hinge Modes in an s-Wave Superconductor Heterostructure.

Second-order topological superconductors host Majorana corner and hinge modes in contrast to conventional edge and surface modes in two and three dimensions. However, the realization of such second-order corner modes usually demands unconventional superconducting pairing or complicated junctions or layered structures. Here we show that Majorana corner modes could be realized using a 2D quantum spin Hall insulator in proximity contact with an s-wave superconductor and subject to an in-plane Zeeman field. Beyond a critical value, the in-plane Zeeman field induces opposite effective Dirac masses between adjacent boundaries, leading to one Majorana mode at each corner. A similar paradigm also applies to 3D topological insulators with the emergence of Majorana hinge states. Avoiding complex superconductor pairing and material structure, our scheme provides an experimentally realistic platform for implementing Majorana corner and hinge states.

Topological Magnon Modes in Patterned Ferrimagnetic Insulator Thin Films.

Manipulation of magnons opens an attractive direction in the future energy-efficient information processing devices. Such quasi-particles can transfer and process information free from the troublesome Ohmic loss in conventional electronic devices. Here, we propose to realize topologically protected magnon modes using the interface between the patterned ferrimagnetic insulator thin films of different configurations without the Dzyaloshinskii-Moriya interaction. The interface thus behaves like a perfect waveguide to conduct the magnon modes lying in the band gap. These modes are immune to backscattering even in sharply bent tracks, robust against the disorders, and maintain a high degree of coherence during propagation. We design a magnonic Mach-Zehnder interferometer, which realizes a continuous change of magnon signal with varying external magnetic field or driving frequency. Our results pave a new way for realizing topologically protected magnon waveguide and finally achieving a scalable low-dissipation spintronic devices and even the magnonic integrated circuit.

Fano resonances in bilayer phosphorene nanoring.

Tunable transport properties and Fano resonances are predicted in a circular bilayer phosphorene nanoring. The conductance exhibits Fano resonances with varying incident energy and applied perpendicular magnetic field. These Fano resonance peaks can be accurately fitted with the well known Fano curves. When a magnetic field is applied to the nanoring, the conductance oscillates periodically with magnetic field which is reminiscent of the Aharonov-Bohm effect. Fano resonances are tightly related to the discrete states in the central nanoring, some of which are tunable by the magnetic field.

Light-Induced Exciton Spin Hall Effect in van der Waals Heterostructures.

We propose a light-induced spin Hall effect for interlayer exciton gas in monolayer MoSe2-WSe2 van der Waals heterostructure. By applying two infrared, spatially varying laser beams coupled to the exciton internal states, a spin-dependent gauge potential on the exciton center-of-mass motion is induced. This gauge potential deflects excitons in different spin states towards opposite directions, leading to a finite spin current but vanishing mass current. In the Hall bar geometry, the spin-dependent deflection gives rise to spin-dependent chiral edge states with spin-velocity locking. The spin current and chiral edge states of the excitons can be detected by spatially resolved photoluminescence spectroscopy.

[Evaluation of total suspended matter based on spectral classification].

Total suspended matter concentration is one of the important parameters of water component. Traditional retrieval model ignored the difference of case 2 water which has complex optical properties. In the present study, we developed a method of water classification based on optical classification using HJ-1 multispectral data. We divided the water into two types and developed a retrieval model suitable for different water type. The results indicate: (1) the accuracy of retrieved results based on spectral classification has been improved; (2) exponential model reflects the relationship between suspended sediment concentration and retrieved factor and is better for type I water, while linear model is better for type II water.

Quantum interference between dark-excitons and zone-edged acoustic phonons in few-layer WS2.

Fano resonance which describes a quantum interference between continuum and discrete states, provides a unique method for studying strongly interacting physics. Here, we report a Fano resonance between dark excitons and zone-edged acoustic phonons in few-layer WS2 by using the resonant Raman technique. The discrete phonons with large momentum at the M-point of the Brillouin zone and the continuum dark exciton states related to the optically forbidden transition at K and Q valleys are coupled by the exciton-phonon interactions. We observe rich Fano resonance behaviors across layers and modes defined by an asymmetry-parameter q: including constructive interference with two mirrored asymmetry Fano peaks (weak coupling, q > 1 and q < - 1), and destructive interference with Fano dip (strong coupling, ∣q∣ < < 1). Our results provide new insight into the exciton-phonon quantum interference in two-dimensional semiconductors, where such interferences play a key role in their transport, optical, and thermodynamic properties.

[Comprehensive Classification Method of Urban Water by Remote Sensing Based on High-Resolution Images].

Urban water is a significant part of the urban ecosystem. Therefore, a comprehensive evaluation method of the water environment was proposed based on domestic high-resolution images. The relationships between the spectral characteristics and water quality parameters of urban water were analyzed based on sampling in Nanjing, Wuxi, Changzhou, and Yangzhou from 2017 to 2019. An index named the U-FUI (urban Forel-Ule index) suitable for urban water based on GF-2 images was proposed to achieve the classification of urban water on the basis of the international standard chroma conversion model and the Forel-Ule index. Independent verification data showed that the recognition accuracy of the classification model could reach 72%. The results indicated that urban water can be classified into six classes from Ⅰ to Ⅵ, which represent water colors of blue, light green, dark green, yellow, yellowish brown, and dark grey, respectively, according to the U-FUI. Among them, the water quality of U-FUI Ⅰ water is good, but is rarely distributed in urban water. The concentrations of chlorophyll-a in U-FUI Ⅱ-Ⅲ water are higher than those of the other classes; the concentrations of total suspended solids, particularly inorganic suspended solids, of U-FUI Ⅳ-Ⅴ water are higher than those of the other classes; and the water quality of U-FUI Ⅵ water is poor and the water quality parameters are different from those of the other classes. Meanwhile, the method was successfully applied to the GF-2 image of Nanjing on April 9, 2018. The results showed that the urban water in Nanjing is mainly composed of U-FUI Ⅱ-Ⅳ water, whereas the distribution of U-FUI Ⅰ, Ⅴ, and Ⅵ water is lower in the city. The spatial distribution characteristics were consistent with the results of in-situ sampling in the same period.

[Analysis of phytoplankton absorption coefficients and their effect factors in Taihu Lake].

To estimate the spatial variation characteristics of Taihu Lake phytoplankton and its influencing factors, samples were taken at 52 sampling sites during Apr. 2009. Then the total concentration of Chla and absorption coefficient of phytoplankton were measured the very day the samples were delivered to the lab. In the present research, results on pigment package effect by former researchers were taken to calculate its influence on specific absorption coefficients, the power of package effect of different areas in Taihu Lake were estimated, and the package effort revision was done to absorption coefficient of phytoplankton. Ratio of blue and red band of absorption coefficients (a(ph) (440)/a(ph) (675)) and standardization specific absorption spectrum were used to measure the influence on specific absorption coefficients by accessory pigment in different areas of Taihu Laik and different bands. Results showed that (1) specific absorption coefficients of phytoplankton in Taihu Lake vary more in short wave bands than that at 675 nm, specific absorption coefficients in Meiliang Bay are lower than in other areas. (2) Spatial variation of specific absorption coefficients in Taihu Lake is seriously influenced by package effect, and this influence occurred more seriously in Meiliang Bay than in other areas and more seriously in alongshore water body than in offshore water body. (3) Influence on specific absorption coefficients by accessory pigment is relatively weak, and mostly concentrates in short wave band, while auxiliary pigment influence is less at 675 nm, and in Meiliang Bay accessory pigment influence is less than in other areas, and its influences are less in alongshore water body than in offshore water body.

[Remote Sensing Classification of Urban Black-odor Water Based on Decision Tree].

Remote sensing monitoring of black-odor water is an important method for understanding the current status of urban water quality, and comprehensively evaluating the effect of urban water environment treatment. A total of 171 samples were collected in Nanjing, Changzhou, Wuxi, and Yangzhou cities and water quality parameters and optical parameters were measured simultaneously. Based on the analysis of the water color and optical characteristics of the black-odor water and non-black-odor water (denoted as general water), a decision tree was constructed to identify the severe, mild black-odor water, and general water as green and yellow water. The results found that:①According to the water color, the water bodies can be divided into six types. Among them, type 1 to 4 water bodies are black-odor water, which are gray black, dark gray, gray, and light gray water, respectively, and type 5 and 6 water bodies are general water, which are green and yellow water, respectively; ②Type 1 water body contains high contents of non-pigmented particulate matter and colored dissolved organic matter(CDOM), however, the absorption of pigmented particulate matter is not dominant. Type 2 and 5 water bodies are dominated by pigmented particulate matter. Type 3, 4, and 6 water bodies are dominated by non-pigmented particulate matter; ③After water color classification, and according to the differences of the reflection spectrums of the six types of water bodies, the difference of black-odorous water index (DBWI), green-red-nir area water index (G-R-NIR AWI), the green band reflectance and the normalized difference black-odorous water index (NDBWI) were used to construct a decision tree to identify the severe, mild black-odor water, and general water; ④The decision tree was applied to the PlanetScope satellite image of Yangzhou City on April 9, 2019, and 10 synchronous sampling points were used for verification. The overall recognition accuracy reached 80.00%, and the K value reached 0.67. The urban water classification model, after water color classification, can be applied to other similar water bodies, and provides a technical method for the supervision of black-odor water bodies.

[Endogenous BDNF promote regeneration of injured nervous system].

OBJECTIVE: To test the effect of endogenous BDNF on injured nervous system. METHODS: The left sciatic nerves of the rats were cut off, and then divided into two groups, each with 8 rats. The rats in the experimental group were intraperitoneally injected with anti-BDNF, while the control group was given normal sheep serum (NSS). The dorsal coclums of the rats were cut on the 8th day. The L5 DRG were cut into length wise sections to dye with fluorescent antibody. Positive cells of GAP-43 in the L5 DRG were counted. The second experiment had both sides of sciatic nerves of the rats cut off, followed by the same procedure as the first experiment. The HRP tracing and ABC immunohistochemical staining were performed to analyse the effect of endogenous BDNF on the recovery of injured spinal cords. RESULTS: For the rats with left sciatic nerves cut off, the experimental group had less GAP-43 positive cells in the left L5 DRG than the controls (P<0.01). For the rats with both sciatic nerves cut off, the experimental group had less nerves with positive fibers-labeled HRP than the controls at the site of tSCI (P<0.01). CONCLUSION: Endogenous BDNF promote the recovery of injured nervous system.

[Application of self-made fine-tuning device in distal locking process of femoral interlocking intramedullary nail].

OBJECTIVE: To evaluate the curative efficacy of self-made fine-tuning setting in the process of femoral distal implantation of intramedullary nail. METHODS: From October 2015 to October 2017, 66 cases of femoral shaft fracture were treated with anterograde interlocking intramedullary nail including 45 males and 21 females with a mean age of(37.21±11.18) years old. Among them, 36 cases were treated with the manufacture's aiming device and self-made fine-tuning setting (research group), other 30 cases were treated with the manufacture's aiming device(control group). The mean operation time, the times of C-arm scan in surgery, the post-operation complications and the fracture union were observed and compared in two groups. RESULTS: Sixty-two cases acquired 8 to 15 months with a mean time of 12.4 months follow-up visit. The post-operation complications and the fracture union between the two groups had no significant difference(P>0.05), the mean operation time and the times of C-arm scan in surgery had statistically significant difference(P<0.05). CONCLUSIONS: Self-made fine-tuning setting in the process of femoral interblocking intramedullary nail could shorten operation time and reduce the the times of C-arm scan.

[Reconstruction of Water Hyperspectral Remote Sensing Reflectance Based on Sparse Representation and Its Application].

Multispectral satellite sensors have several limitations with respect to capturing the target's spectral information due to their band setting and number of bands. The hyperspectral reconstruction technique is an effective method to obtain hyperspectral information from multispectral data. In this study, we propose a hyperspectral reconstruction algorithm based on the sparse representation of water remote sensing reflectance. The proposed algorithm was validated for five ocean color sensors (Sentinel-2A MSI, MERIS, MODIS Aqua, GOCI, and ⅦRS) using in situ measured above-water remote sensing reflectance. The mean absolute percentage error (MAPE) and root mean square error (RMSE) of the reconstructed and measured spectra for five ocean color sensors were less than 10% and 0.005 sr-1, respectively. Compared with the spectra reconstruction algorithm based on multi-variable linear regression, the proposed algorithm can obtain the features of complex water remote sensing reflectance without using in situ-measured reflectance for algorithm tuning. In addition, the accuracy of the proposed algorithm is better than the spectra reconstruction algorithm based on multi-variable linear regression. Two spectra reconstruction algorithms were applied to five ocean color sensors to test the applicability of the remotely estimated water constituent concentration. The statistical results for the reconstructed spectral factors and in situ water constituent concentration suggest that the reconstructed reflectance derived by the proposed algorithm has a performance similar to that of in situ-measured hyperspectral reflectance. The reconstructed reflectance derived by the proposed algorithm performs better than the spectra reconstruction algorithm based on multi-variable linear regression. Finally, the proposed algorithm was applied to GOCI data to remotely estimate the chlorophyll-a and total suspended matter concentrations. The accuracy of the water constituent concentration estimated from reconstructed images is better than that using original multispectral images. For the estimation of the chlorophyll-a concentration, the MAPE improved from 80.6% to 51.5% and the RMSE improved from 12.175 µg·L-1 to 7.125 µg·L-1. For the estimation of total suspended matter, the MAPE improved from 19.1% to 18.8% and the RMSE improved from 29.048 mg·L-1 to 28.596 mg·L-1.

[Preliminary exploring of hyperspectral remote sensing experiment for nitrogen and phosphorus in water].

The content of nitrogen and phosphorus in the waters is an important index to measure water quality, and the technique of remote sensing plays a large role in monitoring the change in environment. The reflectance spectra of nitrogen and phosphorus with different concentrations were measured to discover their special features under pure water condition in the laboratory by hyperspectral remote sensing technique. The result shows that nitrogen has reflectance peaks at 404 and 477 nm, and phosphorus at 350 nm, and these reflectance peaks have a good correlation with their concentrations, then a quantitative retrieval model was deduced for nitrogen and phosphorus based on that. These results will lay an important basis for further monitoring nitrogen and phosphorus by remote sensing technique in the big inland lakes, reservoirs and rivers.

[Analysis of Absorption Characteristics of Urban Black-odor Water].

The urban black-odor water body has become a serious problem of urban water environment and identifying their optical characteristics in urban areas is the prerequisite and basis for their detection by remote sensing. A total of 85 samples of urban black-odor water, from Changsha, Nanjing, and Wuxi, were collected from 2016 to 2017, and a total of 80 samples were collected from non-black-odor (smelly) water samples. The water quality parameters such as suspended matter and the absorption coefficient were measured. The results showed that:①The total black-odor water body particulate matter absorption coefficients and non-pigmented particulate matter absorption coefficients were generally higher than those for non-black-odor water bodies and they had a certain degree of discrimination at 440 nm, but their effect was not significant. The absorption of relatively high levels of particulate matter in black-odor water was mainly due to high absorption of non-pigmented particles. In the data collected, non-pigmented particles in black-odor water accounted for more than 50% of the total particles. ② The Colored Dissolved Organic Matter (CDOM) absorption coefficients for black-odor water bodies and non-black-odor water bodies differed. The average absorption coefficient of CDOM at 440 nm for black-odor water bodies was 1.7 times higher than that for non-black-odor water bodies. Thus, the black-odor water body can be distinguished by using the slope of the absorption coefficient curve fitted in the characteristic wavelength band of 440 nm, as well as in different wavelength bands; the overall effect is good. However, as the wavelength increases, the discrimination effect decreases. Analysis of the absorption characteristics of urban black-odor water bodies will provide effective technical support for their detection by remote sensing and supervision, and the density of CDOM in black-odor water was generally high, which could be used as an important reference for identification.

[Remote Sensing Identification of Urban Black-Odor Water Bodies Based on High-Resolution Images:A Case Study in Nanjing].

The identification of urban black-odor water bodies plays an important role in monitoring and controlling black-odor water bodies. In 2016, a ground survey was conducted on the urban reach of Nanjing, and 55 samples from the West Shazhou River, Tuwei River, Xuanwu Lake, and Jinchuan River were obtained. The spectral characteristics of urban black-odor water bodies and other water bodies were analyzed. Recognition algorithms for GF-2 data were proposed in order to analyze the spatial distribution and environmental factors of urban black-odor water bodies. These algorithms were single-band thresholds based on reflectance of the green band, the difference between the blue band and green band, the ratio of the green band and red band, and the chromaticity value. The results indicate that:① compared with other types of water, the urban black-odor water has the smallest spectral slope in the range of 400-500 nm and lowest reflectivity, and the peaks and valleys are not prominent in the whole visible range; ② based on the verification, the accuracy of the ratio algorithm is the highest; and ③ using the ratio algorithm to calculate the GF-2 data of November 3, 2016, a total of 11 black river sections are identified. The entire length is 40.7 km, and the area is 0.749 km2.The black-odor water sections are distributed over a wide range but are not continuous, and they are concentrated in the densely populated areas. Domestic sewage, industrial waste water, and broken river channel are the main reasons.

[Remote Sensing of Chlorophyll-a Concentrations in Lake Hongze Using Long Time Series MERIS Observations].

Chlorophyll-a (Chl-a) concentrations are usually measured as the proxy of phytoplankton biomass and used to evaluate the trophic status of inland waters. Based on 49 in situ samples taken from two measurement campaigns in Lake Hongze in 2016, we evaluate the performance of five Chl-a estimation algorithms (including the band ratio, three-band, FLH algorithm, MCI, and UMOC algorithms). The results showed that the UMOC model was the most suitable model for the estimation of Chl-a in Lake Hongze. The mean relative error (MRE) of UMOC was 32.30%, much lower than the band ratio algorithm (75.17%), three-band algorithm (62.44%), FLH algorithm (45.87%), and MCI algorithm (56.95%). The best-performing UMOC model was applied to the atmospherically corrected 689 MERIS images between 2002-2012 and long time series MERIS Chl-a concentration estimation products were acquired. Between 2002 and 2012, the mean Chl-a concentration in Lake Hongze was 19.560 mg·m-3 with substantial spatial and temporal variability. Based on the variability of monthly mean Chl-a concentrations in each pixel, the Lake Hongze waterbody was divided into three water types, Region A, Region B, and Region C. The annual mean Chl-a concentrations of Region B and Region C showed no significant changes, while the concentrations in Region A increased markedly. The analysis of the meteorological factors showed that the fluctuations of the annual mean Chl-a concentrations in Region B and Region C were mainly affected by annual precipitation, suggesting that the Chl-a concentrations of these two regions are dominated by the intensity of the lake flow. The annual mean Chl-a concentrations of Region A showed a strong negative correlation with the annual mean wind speed. The descending trend of the annual wind speed may enhance the eutrophication degree of this region, threatening the safety of the water quality of the South-North Water Transfer Project. The Chl-a concentrations showed a strong positive correlation with the distance from the Huaihe Estuary in the wet season suggesting that the Huaihe River has an obvious inhibitory effect on algal biomass in Lake Hongze during this period.

[Inversion Model and Daily Variation of Total Phosphorus Concentrations in Taihu Lake Based on GOCI Data].

The TP concentration is an important index of water quality and an important influencing factor of eutrophication and algae blooms. Remote sensing technology has advantages of wide scope and high time limited efficacy. Monitoring the concentration of TP by satellite remote sensing is important for the study of water quality and eutrophication. In situ datasets collected during the three times of experiments in Taihu Lake between 2013 and 2014 were used to develop the TP inversion model based on GOCI data. The GOCI data in spring, summer, autumn and winter in 2014 were selected to analyze the time and space changes of TP concentration in Taihu Lake. The results showed that the TP algorithm was built up based on the variables, which was to use the eight band combination of GOCI data as variable, and build model using Multi factor linear regression method. The algorithm achieved more accurate TP estimation with R² = 0.898, MAPE = 14.296%, RMSE = 0.026 mg · L⁻¹. Meantime, a analysis on the precision of the model by using the measured sample points and the synchronous satellite images with MAPE = 33.642%, 22.551%, RMSE = 0.076 mg · L⁻¹, 0.028 mg · L⁻¹ on August 5, 2014 and October 24, 2014. Through the analysis of the 30 images on the four days of the four seasons, it showed that the absolute concentration of total phosphorus was different in different seasons. But temporal and spatial distribution of total phosphorus concentration was similar in the morning and afternoon. In spatial distribution, the TP concentration in Meiliang Bay, Zhushan Bay, Gonghu Bay, Xiaomei Port and Changdou Port in the southwest coast was at a continuously high position. The TP concentration change in different regions was influenced by wind direction, wind speed and other factors. The TP concentration highest in the morning, and then gradually decreased, this phenomenon reflected that the TP concentration was affected by temperature and light.

[Absorption and Reflection Characteristics of Black Water Blooms in the Eutrophic Water].

Studying on optical properties of black water blooms, is the precondition for using remote sensing technology to monitor and evaluate the black water blooms event. Black water blooms occurred in Taihu Lake in July 2015. A total of 36 water samples were observed in the three water regions of Taihu Lake, the region 1 with black water blooms characteristics, region 2 with cyanobacterial bloom characteristics, and regional 3 with characteristics of clean lake water. The reflectance spectra and absorption coefficient of these three regions were analyzed, and the results show that:1 The absorption coefficients of the total particles, the pigment particles and the non-pigment particlesin black water blooms are 1 to 2 times higher than the other two areas. The absorption coefficient of CDOM between 400-500 nm in region 1 is about 2 times higher than the other two areas, which lead the black water area with a very lower reflectance, and presents as black color. 2 The range of M value in black water blooms is lower than Dianchi Lake and Chaohu Lake, which means the humic acid content of CDOM with black water characteristics is higher. A significant positive correlation is found between chlorophyll a (Chl-a) and the CDOM absorption coefficient at 350 nm, indicating that algae degradation is likely to be the primary source of CDOM in black waters. 3 The contribution of each optically active component indicates that the water absorption of region 1 strongly controlled by CDOM below 380 nm, but by Chla absorption between 380 nm and 700 nm.