Search

Satellite-based precipitation products (SPPs) have great potential in water-related applications, especially in ungauged/poor-gauged basins. Three SPPs, namely integrated multisatellite retrieval for the global precipitation measurement (GPM) mission, tropical rainfall measuring mission multisatellite precipitation analysis version 7, and precipitation estimation from remotely sensed information using artificial neural networks—climate data record, were evaluated over the lower Mekong river basin (LMB) from January 4, 2014 to February 28, 2017 at daily and monthly scales. Daily rainfall data collected from 119 rain gauges in the LMB were used to conduct a pixel-point comparison. Daily discharge observations at six stream gauges, together with a well-calibrated distributed hydrological model, were used to evaluate the hydrological utilities of the three SPP s. The results convey that: integrated multisatellite retrieval for the GPM mission shows more stable and precise estimation of precipitation in pixel-point comparisons (for both all rainfall events and only heavy rain events) than the other two SPP s; precipitation estimation from remotely sensed information using artificial neural networks—climate data record overestimates the rainfall amounts in LMB seriously by 17%; and integrated multisatellite retrieval for the GPM mission performs better than other two SPP s when forcing hydrological model to simulate discharges with more stable and accurate discharge results (daily Nash–Sutcliffe efficiency coefficient larger than 0.73 and monthly Nash–Sutcliffe efficiency coefficient larger than 0.84).

The detection of topological phases of matter has become a central issue in recent years. Conventionally, the realization of a specific topological phase in condensed matter physics relies on probing the underlying surface band dispersion or quantum transport signature of a real material, which may be imperfect or even absent. On the other hand, quantum simulation offers an alternative approach to directly measure the topological invariant on a universal quantum computer. However, experimentally demonstrating high-dimensional topological phases remains a challenge due to the technical limitations of current experimental platforms. Here, we investigate the three-dimensional topological insulators in the AIII (chiral unitary) symmetry class, which yet lack experimental realization. Using the nuclear magnetic resonance system, we experimentally demonstrate their topological properties, where a dynamical quenching approach is adopted and the dynamical bulk-boundary correspondence in the momentum space is observed. As a result, the topological invariants are measured with high precision on the band-inversion surface, exhibiting robustness to the decoherence effect. Our Letter paves the way toward the quantum simulation of topological phases of matter in higher dimensions and more complex systems through controllable quantum phases transitions.

Soil erosion is one of the most significant environmental problems in China. From 2010 to 2012, the fourth national census for soil erosion sampled 32 364 PSUs (Primary Sampling Units, small watersheds) with the areas of 0.2–3 km2. Land use and soil erosion controlling factors including rainfall erosivity, soil erodibility, slope length, slope steepness, biological practice, engineering practice, and tillage practice for the PSUs were surveyed, and the soil loss rate for each land use in the PSUs was estimated using an empirical model, the Chinese Soil Loss Equation (CSLE). Though the information collected from the sample units can be aggregated to estimate soil erosion conditions on a large scale; the problem of estimating soil erosion condition on a regional scale has not been addressed well. The aim of this study is to introduce a new model-based regional soil erosion assessment method combining a sample survey and geostatistics. We compared seven spatial interpolation models based on the bivariate penalized spline over triangulation (BPST) method to generate a regional soil erosion assessment from the PSUs. Shaanxi Province (3116 PSUs) in China was selected for the comparison and assessment as it is one of the areas with the most serious erosion problem. Ten-fold cross-validation based on the PSU data showed the model assisted by the land use, rainfall erosivity factor (R), soil erodibility factor (K), slope steepness factor (S), and slope length factor (L) derived from a 1 : 10 000 topography map is the best one, with the model efficiency coefficient (ME) being 0.75 and the MSE being 55.8 % of that for the model assisted by the land use alone. Among four erosion factors as the covariates, the S factor contributed the most information, followed by K and L factors, and R factor made almost no contribution to the spatial estimation of soil loss. The LS factor derived from 30 or 90 m Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data worsened the estimation when used as the covariates for the interpolation of soil loss. Due to the unavailability of a 1 : 10 000 topography map for the entire area in this study, the model assisted by the land use, R, and K factors, with a resolution of 250 m, was used to generate the regional assessment of the soil erosion for Shaanxi Province. It demonstrated that 54.3 % of total land in Shaanxi Province had annual soil loss equal to or greater than 5 t ha−1 yr−1. High (20–40 t ha−1 yr−1), severe (40–80 t ha−1 yr−1), and extreme ( > 80 t ha−1 yr−1) erosion occupied 14.0 % of the total land. The dry land and irrigated land, forest, shrubland, and grassland in Shaanxi Province had mean soil loss rates of 21.77, 3.51, 10.00, and 7.27 t ha−1 yr−1, respectively. Annual soil loss was about 207.3 Mt in Shaanxi Province, with 68.9 % of soil loss originating from the farmlands and grasslands in Yan'an and Yulin districts in the northern Loess Plateau region and Ankang and Hanzhong districts in the southern Qingba mountainous region. This methodology provides a more accurate regional soil erosion assessment and can help policymakers to take effective measures to mediate soil erosion risks.

We present a high-sensitivity and high-accuracy D-shaped polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure (i.e., bottom, inter-, and surface layers) and a rough inter-layer surface in the sensing region. The surface layer is made of dilute Canada balsam in xylene, and the longitudinal section is coated with light-absorbing (LA) film. To obtain the maximum sensitivity and accuracy, the morphologies of the inter-layer and surface layer are determined. The effects of coating thickness and the refractive index of the surface layer and LA film on the performance of FOEW sensors are investigated both theoretically and experimentally. The sensitivity, accuracy and repeatability of the sensors are evaluated using glucose solutions; the response of the sensors, which are self-assembled from the polycation (tris[2-(4-phenyldiazenyl) phenylaminoethoxy] cyclotriveratrylene (TPC) plus poly dimethyl diallyl ammonium chloride (PDDAC)) and polyanion (TPC plus polyacrylic acid (PAA)), to Hg(II) in aqueous solutions is examined. The results highlighted the high sensitivity of the FOEW sensor with a three-layer structure and appropriate roughness of the inter-layer surface, which showed a 6.5-fold improvement in the detection of the target Hg(II) ions compared to the conventional FOEW sensor with a core-cladding structure, and the novel sensor was validated with a lower limit of detection of 0.1 mg L −1 .

Global observations of near-surface air temperature and specific humidity over land are needed for a variety of applications, including to constrain global estimates of evapotranspiration (ET). Spaceborne hyperspectral observations, such as those from NASA's Atmospheric Infrared Sounder (AIRS) mission, show promise for meeting this need, yet there are surprisingly few validation studies of AIRS near-surface atmospheric state retrievals. In this study, we use triple collocation to validate AIRS Level 3 retrievals of near-surface atmospheric state over land using twelve years of gridded station observations and two reanalyses. Deseasonalized AIRS retrievals correlate well with deseasonalized ground observations outside the tropics, but correlate less well in the tropics. Lower temporal sensitivity near the surface in the tropics contributes to the lower correlation for near-surface air temperature and is consistent with known physics of the tropical atmosphere, in which temperatures outside the boundary layer (which dominate the AIRS retrieval signal) are poorly correlated with those near the surface. Retrievals in the tropics may also be more susceptible to errors in cloud-clearing algorithms, and to uncertainty in surface emissivity. Since ET is greatest in the tropics, and tropical measurement networks are particularly sparse, this work motivates new approaches for measuring ET in the tropics.

To monitor biofilm growth on polydimethylsiloxane in a photobioreactor effectively, the biofilm cells and liquids were separated and measured using a sensor with two U-shaped, double-tapered, fiber-optic probes (Sen. and Ref. probes). The probes’ Au-coated hemispherical tips enabled double-pass evanescent field absorption. The Sen. probe sensed the cells and liquids inside the biofilm. The polyimide–silica hybrid-film-coated Ref. probe separated the liquids from the biofilm cells and analyzed the liquid concentration. The biofilm structure and active biomass were also examined to confirm the effectiveness of the measurement using a simulation model. The sensor was found to effectively respond to the biofilm growth in the adsorption through exponential phases at thicknesses of 0–536 μm.

In this study, the latest released satellite based precipitation products - Global Precipitation Measurement (GPM) mission Level 3 product Integrated Multi-satellitE Retrievals for GPM (IMERG) and version 7 of Tropic Rainfall Measurement Mission (TRMM 3B42V7) data is evaluated and applied with a distributed hydrological model to examine the precipitation detection and performance in hydrological simulating over the Mekong River Basin (MRB) during 2014/4/1 to 2016/1/31. About 137 rain gauges stations were collected to carry out a pixel-point comparison between observation and satellite precipitation. Moreover, daily discharge observation data from five discharge gauges were used to evaluate the performance of hydrological simulation. The result demonstrate that: 1) IMERG data show more precision in both heavy and light rain detection than 3B42V7; 2) IMERG performs better than 3B42V7 when driving hydrologic model, giving the fact that the simulated discharge result from IMERG is more accurate and stable.

Aging of the composite insulator threatens the safety of power grid. A portable nuclear magnetic resonance (NMR) sensor with an adjustable ‘clamp’ structure is constructed for the noninvasive measurement of the aging status of the composite insulator. Two cylindrical permanent magnets are used to establish static magnetic field B0. Magnets can be adjusted to adapt to different thickness of sheds. An “8-shaped” plane radio frequency (RF) coil is used. Composite insulator samples of different service time are measured. Their nuclear magnetic resonance (NMR) echo decay signal was collected, and the decay signal was fitted with an exponential function. After this processing the transverse relaxation time (T2) was obtained. For comparison, the relative permittivity of the samples is measured by an Agilent 4294A. The result in demonstrates that an increase in the aging level of composite insulator results in a decrease of T2. The trend of transverse relaxation time T2 is the same as that of the relative permittivity. The field test results show that NMR sensor can be used to detect the aging status of composite insulator shed. The T2 obtained by our portable NMR sensor can reliably be used as an index to reflect the aging status of composite insulator.

The flashover of polluted insulators is a serious threat to the safe operation of overhead power lines. The leakage current on surface of insulators is closely related to the developing process of pollution flashover, affected by many factors, such as wetting degree, system voltage and structures of insulators. At the same time, the leakage current is easy to be monitored on-line continuously. Hence, as one of on-line monitoring methods for polluted insulators. Based on artificial pollution tests under different relative humidity (RH) and salt deposit density (SDD), a method incorporates S-transform and support vector machine (SVM) for evaluating safety condition of polluted insulators is proposed. Firstly, the approach utilizes S-transform to extract the amplitude Ih, phase θ and total harmonic distortion (THD) of leakage current. Then the I h , θ and THD are as characteristic parameters to put into SVM, the output parameters of SVM are fuzzifled into four fuzzy subsets for evaluating safety condition of polluted insulators. Lastly, the performance of SVM is validated by 8 pairs of testing samples, and the influences of SDD and RH on the performance of insulators are discussed. The results show that, the leakage current becomes inductive when strong local arcs occur, decreases with the increase of RH, and Ih has no relation with SDD when the RH is low but increases with the increase of SDD when RH is high. THD of leakage current increases slowly with the increase of RH when the pollution is light, but decreases firstly and then increases with the increase of RH when the pollution is middle or heavy, THD take the minimum at the RH of about 80%.

Although the numerous advantages of polymer optical fiber (POF) sensors have been applied in different fields, the measurement consistency and sensitivity of POF evanescent wave (EW) sensors are still affected by its thermal stability and water absorption. Therefore, we perform a study to demonstrate the mechanism of the effect of heat treatments on physical and optical properties of POF EW sensors. We investigate the surface morphology, composition, refractive index, geometry, and weight of the fiber-sensing region subjected to water and vacuum heat treatments. We examine the spectral transmission and transmitted light intensity of POF sensors. We present a theoretical investigation of the effect of heat treatments on the sensitivity of POF EW sensors. The performance of the prepared sensor is evaluated using glucose and Chlorella pyrenoidosa analytes. We discovered that the spectral transmission and transmitted light intensity of the fibers shows little effect of vacuum heat treatments. In particular, the sensors, which subject to vacuum heat treatment at 110 °C for 3 h, exhibit temperature-independent measuring consistency and high sensitivity in glucose solutions in the temperature range 15–60 °C and also show high sensitivity in Chlorella pyrenoidosa solutions.

In this paper, we present a high-sensitivity polymer fiber-optic evanescent wave (FOEW) sensor with a three-layer structure that includes bottom, inter-, and surface layers in the sensing region. The bottom layer and inter-layer are POFs composed of standard cladding and the core of the plastic optical fiber, and the surface layer is made of dilute Canada balsam in xylene doped with GeO2. We examine the morphology of the doped GeO2, the refractive index and composition of the surface layer and the surface luminous properties of the sensing region. We investigate the effects of the content and morphology of the GeO2 particles on the sensitivity of the FOEW sensors by using glucose solutions. In addition, we examine the response of sensors incubated with staphylococcal protein A plus mouse IgG isotype to goat anti-mouse IgG solutions. Results indicate very good sensitivity of the three-layer FOEW sensor, which showed a 3.91-fold improvement in the detection of the target antibody relative to a conventional sensor with a core-cladding structure, and the novel sensor showed a lower limit of detection of 0.2ng/l and a response time around 320s. The application of this high-sensitivity FOEW sensor can be extended to biodefense, disease diagnosis, biomedical and biochemical analysis.