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Due to rapid development, the occurrence of flood has become more and more frequent. However, due to the complex nature and limited knowledge, the conventional hydrological model for flood forecasting purposes faces drawbacks in terms of technical difficulties. Hence, it is essential to have a model which can provide a considerably high level of accuracy for flood forecasting. This study selected the area between the Xiangtan station and Changsha station, located in Xiangjiang River as the study area. Recurrent neural network (RNN), gated recurrent unit (GRU) and long short-term memory (LSTM) were applied for model development purposes. The models were used to forecast the flood disasters occurring in 2017, 2019, 2020 and 2022 for 1h, 6h and 12h in advance. A series of statistical analyses have been conducted to evaluate the model performance. The LSTM model outperformed than the RNN and GRU models. In terms of the overall analysis, the LSTM model achieved relatively good accuracy with a NSE of above 0.98, and RMSE of lower than 0.2 m. In addition, the model with a 6h in advance is the most suitable model to predict the peak flood arrival time with an absolute error of less than 3 hours. [ABSTRACT FROM AUTHOR]

Doping is known as an effective approach to extend the knowledge of structures and properties of clusters. Herein, Ge-doped boron clusters and their anions GeBn0/− with n = 6–20 are systematically investigated by using a spin-polarized density functional theory method to understand their structural evolution and electronic properties. The lowest-energy structures of GeBn and GeBn− clusters are globally searched with genetic algorithm. The doping of a Ge atom has significantly affected the growth behaviors of GeBn0/− clusters, leading to a structural evolution from three-dimensional configuration with a hypercoordinated Ge atom to planar or qusi-planar geometry and finally endohedral cage, in which Ge atom prefers the peripheral site or off-center position. Relative stability analysis identifies that GeB8, GeB10, GeB18, GeB7−, GeB9−, and GeB17− are magic clusters. The magnetic moments of GeBn and GeBn− clusters exhibit an evident odd–even oscillation behavior with cluster size, which is closely related to the interaction between the electronic states of Ge and B atoms. The simulated photoelectron spectra for GeBn− clusters can provide a valuable guidance for further experimental and theoretical research. [ABSTRACT FROM AUTHOR]

Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin–orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally. [ABSTRACT FROM AUTHOR]

This paper presents an adaptive neural network dynamic surface controller for four-Macanum-wheeled omnidirectional mobile robots (MWOMRs) trajectory tracking with full state constraints and input saturation. First of all, an adaptive dynamic surface controller is proposed for the MIMO nonlinear systems with uncertainties and disturbances. The neural network is utilized to approximate the uncertain dynamics. A second-order tracking differentiator, instead of the traditional first-order filter, is introduced to overcome the problem of "explosion of complexity" in back-stepping technique and reduce the filtering error. By employing a barrier Lyapunov function and an auxiliary compensator based on Nussbaum function, the full state constraints and input saturation of the MWOMRs are not violated. Moreover, it is proved that all the signals in the closed-loop system with suitable parameters are semi-global uniformly bounded and the tracking error converges to an arbitrarily small compact set to zero. Finally, experiment results are presented to verify the effectiveness and robustness of the proposed adaptive control approach. [ABSTRACT FROM AUTHOR]

A nonlinear control method is proposed to solve the problem of serious dust pollution and poor diffusion effect in a mining area. Based on the mathematical model of PID control, gain parameters are obtained. The hyperbolic secant function is used to optimize the gain parameters. The dust content error and the dust content error change rate are taken as the input of the nonlinear model; The parameters of dusty gas are obtained by the Ziegler-Nichols tuning method, and the nonlinear gain is set after debugging and modification. The limit value of the function and the nonlinear gain parameter function are obtained. Based on the nonlinear gain parameter function, the nonlinear PID control mathematical model of dust diffusion is established, and the control of dust diffusion is realized. The experimental results show that the minimum average relative error is 1.385%, and the average square error is 2.476%, which is controlled within 9.7162 ms, and the visibility of the control area is good. [ABSTRACT FROM AUTHOR]

Background and aims: Dissolved organic nitrogen (DON) has been increasingly recognized as a crucial component of the terrestrial nitrogen (N) cycle that regulates the ecosystem feedback to climate change. Yet, little information is available about the factors that control soil DON in the alpine ecosystems of the Tibetan Plateau, a region that is extremely sensitive to climate change. Methods: Here, we examined the relationship between DON and climate, plant, and soil attributes along a precipitation gradient in five alpine ecosystems (alpine wetland, alpine meadow, alpine shrub, alpine steppe, and alpine desert) across 20 sites that were up to 4000 km apart on the Tibetan Plateau. Results: Results showed that soil DON concentration varied significantly across these alpine ecosystems, and had a positive relationship with mean annual precipitation. Belowground biomass, soil moisture, micro biomass carbon (MBC), and soil total phosphorus (TP) explained 84% of the variation in DON concentrations. The percentage of DON in soil total dissolved N (TDN) varied with vegetation type, with the lowest percentage observed in the alpine meadow (52%) and the highest in the alpine desert (77%), indicating the slow turnover of DON into inorganic N in systems with low litter input and microbial activity. Conclusions: Precipitation and plant biomass input determine the concentration and turnover of soil DON on the Tibetan Plateau. A warmer and wetter climate that has been predicted for the Tibetan grasslands may lead to a larger and more active DON pool. [ABSTRACT FROM AUTHOR]

Phase-induced polarization modulation has been achieved experimentally by means of the all-optical holographic method. An extra spiral phase is added to a Gaussian beam and then a holographic grating is recorded through the interference of a Gaussian beam and the phase-vortex beam with the same linear polarization state in an azobenzene liquid-crystalline film. We report here that the polarization state of the diffraction light from the recorded grating is different from that of the incident light, while no polarization variation occurs for the holographic grating recorded by two Gaussian beams. The phase-induced polarization modulation is mainly attributed to the formation of birefringence in the film generated by phase vortex, which is investigated through the ripple patterns resulting from the competition between photoinduced torques and analysed by the Jones matrix. The experimental results could enrich the connotation between optical parameters and offer a method to realize polarization modulation through phase control. [ABSTRACT FROM AUTHOR]

Bimetallic nanoparticles have attracted increasing interest because of their unique optical, electronic, magnetic, and catalytic properties which are different from that of their individual constituent metals. In this paper, we report a facile route to the synthesis of Pd-covered and Pd-tipped gold nanorods (AuNRs). And finite-different time-domain (FDTD) is also applied to simulate the longitudinal surface plasmon resonance (SPR) characteristics for two different layered growth modes. The simulated absorption spectra agree with the experimental results. For the Pd-covered AuNRs, it is found that the SPR shows a red-shift with shell thickness less than 2 nm. And then, the SPR blue-shifts and gradually approaches to the absorption peak of Pd nanocuboids with increasing Pd shell thickness. While the SPR of Pd-tipped AuNRs red-shifts with increasing Pd tip-particle size, it is revealed that the bimetallic Au@Pd NRs have higher refractive index sensitivities than that of AuNR cores. The tunable SPR and higher refractive index sensitivities of bimetallic Au@Pd NRs may lead to great potential applications in many Pd-catalyzed reactions and provide an important reference of Pd nanostructures for SPR-based sensing. [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen (N) limitation leads to intense competition between plants and soil microorganisms for available N. However, it is unclear how grazing affects the acquisition of N by plants and microorganisms. Methods: We conducted short-term N tracer experiments during the growing season (June, early growing season; July, mid-growing season; and September, late growing season) in an alpine grassland on the Tibetan Plateau to investigate the effects of grazing on the acquisition of NO -N, NH -N, and glycine-N by plants and soil microorganisms. Three dominant plant species (one graminoid, Kobresia pygmaea, and two forbs, Potentilla bifurca and Potentilla multifida) were selected for the study. As these species represented >90% of the vegetation, the plant recovery of N reflected competition at the plant community. Results: Grazing decreased the recovery of N by soil microorganisms and plants by 46 and 69%, respectively, indicating that grazing strongly reduced the uptake of N by plants and microorganisms and altered the partitioning of N between them. Significant interactions were found between grazing, season and the different forms of N. In the absence of grazing, plants acquired relatively more N than soil microorganisms for the three forms of N in July and September, whereas the microorganisms obtained relatively more N glycine in July and all three forms of N in September under grazing conditions. Under grazing, the plant root biomass played an important role in controlling plant-microbial N acquisition. Conclusions: Grazing alters the partitioning of inorganic and organic N between plants and soil microorganisms by reducing microbial N recovery to a lesser extent than plant N recovery. This indicates that heterotrophic microorganisms play an important part in N cycling in N-limited ecosystems. [ABSTRACT FROM AUTHOR]

An alkylamine-mediated hydrothermal synthesis method is proposed for fabrication of copper (Cu) nanopolyhedrons (including tetrahedral and cubic shapes) with well-defined facets and controllable size by modulating the coordination chemistry of a sole ligand (hexadecylamine, HDA) or dual ligands [HDA and octadecylamine (ODA)]. The size of the nanopolyhedrons increases with decreasing HDA/ODA mole ratio. Both the nanocubes and nanotetrahedrons are single-crystal structures, bound by six {100} or four {111} facets, respectively. The complexation reaction temperature plays a vital role in determining the final morphology of the as-prepared nanocrystals. High complexation reaction temperature is suitable for generation of single-crystalline Cu nuclei and their further growth into nanocubes and nanotetrahedrons, while low temperature leads to formation of multitwinned crystal seeds that finally develop into nanowires. Moreover, the probable aggregative growth is discussed to explain the growth mechanism of the Cu nanopolyhedrons. In addition, double surface plasmon resonance peaks are observed in the absorbance spectra for the Cu nanopolyhedrons with relatively large size. Finite-difference time-domain simulations reveal that the experimental absorption spectra are the superposition of those for nanocubes and nanotetrahedrons in different proportions. The peak at about 600 nm in the experimental spectra mainly originates from the Cu nanocubes, while the absorption from 750 to 950 nm derives from the Cu nanotetrahedrons. These angular Cu nanocubes and nanotetrahedrons may have potential applications in surface-enhanced Raman scattering and catalysis. Graphical Abstract: [ABSTRACT FROM AUTHOR]

In this paper, Ag nanorods (AgNRs) with different aspect ratios (ARs) were prepared by a seed-mediated fast growth approach. The possible growth mechanism of Ag nanostructures was proposed. With a strong interaction between CTAB and Ag seeds, the reduced Ag atoms agglomerated and attached to the performed Ag nanoparticles, where CTAB molecule layer plays a role of rod-like micelles template, leading to one dimensional growth of Ag atoms into AgNRs. The influences of the reaction conditions were discussed on the yield of AgNRs. The surface plasmon resonance (SPR) of AgNRs was studied by finite-difference time-domain (FDTD) simulations. The simulated results indicate that the transverse surface plasmon resonance (SPR) has no obvious shifting, whereas the longitudinal surface plasmon resonance (SPR) shows a significant redshift with the increase of AR of AgNRs, which agrees well with the experimental variation trend. It is also found that the absorption and scattering of AgNRs are stronger than that of Au nanorods (AuNRs), which is in accordance with the Raman signal enhancement by AgNRs compared with that of AuNRs, indicating that AgNR is a promising candidate in bio-molecular detection. [ABSTRACT FROM AUTHOR]

To study how grazing affects the uptake of inorganic and organic N forms, three focal plant species (i.e., the graminoid species Kobresia pygmaea, which decreases with grazing, and the forbs Potentilla bifurca and Potentilla multifida, which increase with grazing) were selected in ungrazed and grazed plots in an alpine meadow on the Tibetan Plateau. Three times during the growing season (i.e., June, July, and September), these plots were injected with N-labeled NO-N, NH-N, or glycine-N, or with only water as a control. Two hours after N injection, exchangeable NH-N, glycine-N, and NO-N as well as plant and soil samples were collected and analyzed for N/N and total N content. Our result showed that all three plant species took up glycine-N, but uptake of inorganic N was generally predominant. The graminoid K. pygmaea took up all three N forms equally in June but preferred NO-N in July (particularly under grazing) and exchangeable NH-N in September. The forbs P. bifurca and P. multifida preferentially took up exchangeable NH-N in July (particularly under grazing), while NO-N was the dominant form of N uptake in September. P. bifurca generally preferred exchangeable NH-N, but preference shifted toward NO-N under grazing in June. P. multifida preferred glycine-N in ungrazed plots and shifted its preference to NO-N under grazing in June. In conclusion, the three plant species showed niche partitioning for uptake of three forms of N across the season, which was modified by grazing. These findings indicate that plant N uptake patterns should be considered for better understanding the mechanisms of grazing effects on plant diversity and species coexistence. [ABSTRACT FROM AUTHOR]

The nonlinear optical properties of an azobenzene-containing ionic liquid crystalline polymer were investigated by a single beam Z-scan technique employing 38 ps and 6 ns laser pulses at 532 nm. The polymer film exhibited large nonlinear refraction and negligible nonlinear absorption under both ps and ns pulses excitation. The nonlinear refractive indices of the polymer were in the order of $$10^{-11} \hbox {cm}^{2}/\hbox {W}$$ under ps excitation and $$10^{-8}\hbox {cm}^{2}/\hbox {W}$$ under ns excitation, respectively. The mechanism accounting for the process of nonlinear refraction was discussed in terms of photoinduced trans-cis transformation and thermal effect. [ABSTRACT FROM AUTHOR]

The flow stress behaviors of squeeze casting SiC/2A50 matrix composites were investigated by means of compression tests on a Gleeble 1500 therma1 mechanical simulator at isothermal constant strain rates ranging from of 0.001 to 1.0 with the testing temperature ranging from 350 to 500°C. The experiments showed that the relationship between stress and strain was obviously influenced by the strain rate and temperature. Dynamic recrystallization generally occurred at a higher temperature and a 1ower strain rate. A linear equation could be fitted between the Zener-Hollomon parameter Z and stress in the experiments. The mean value reciprocal of temperature at every true strain had a linear relation with natural logarithm of Z parameter, and the correlation coefficient, R=0.99, which was very significant by examination. The hot deformation activation energy of SiC/2A50 matrix composites was 163.47 KJ/mol by calculation. [ABSTRACT FROM AUTHOR]