The twin-field (TF) quantum key distribution (QKD) protocol and its variants are highly attractive because they can beat the well-known fundamental limit of the secret key rate for point-to-point QKD ...without quantum repeaters (repeaterless bound). In this Letter, we perform a proof-of-principle experimental demonstration of TFQKD based on the protocol proposed by Curty, Azuma, and Lo, which removes the need for postselection on the matching of a global phase from the original TFQKD scheme and can deliver a high secret key rate. Furthermore, we employ a Sagnac loop structure to help overcome the major difficulty in the practical implementation of TFQKD, namely, the need to stabilize the phase of the quantum state over kilometers of fiber. As a proof-of-principle demonstration, the estimated secure key rate from our experimental TFQKD data at the high loss region surpasses the repeaterless bound of QKD with current technology.
The stable operation of a variable frequency pump is of great importance to the management of a water supply project. Analyzing the operation performance based on monitoring data is necessary for ...maintaining the stable operation of a variable frequency pump. Several sensors are installed at six monitoring points on the pump to collect signals including vibration velocity, vibration acceleration and vibration displacement. Monitoring signals are preprocessed by smoothing, adjusting waveform trend and filtering on the basis of Fast Fourier Transform (FFT). Then, the vibration features are extracted by power spectrum analysis and cepstrum analysis methods. According to the extracted features, the vibration law and actual operation performance of a variable frequency pump under different operating conditions are analyzed. Results indicate that the vibration amplitude of the pump varies sharply under the operating conditions of 15 Hz, 20 Hz and 30 Hz, 35 Hz. The operating condition of 0 Hz, 15 Hz is the restricted operating area of the pump. The vibration and noise continue increasing under the operating conditions of 35 Hz, 50 Hz and reach the maximum values at 50 Hz. Therefore, the optimal operating is within the range of 20 Hz, 30 Hz. Finally, by analyzing the critical values of the operating conditions, the fault diagnosis and the evaluation of the operating status are conducted.
•Simulation the river habitat quality in Luanhe based on the eco-hydrodynamic model.•Constructing a two-dimensional (2D) eco-hydrodynamic model.•The habitat suitability indices (HSIs) of various ...target species were determined.•The spatial distribution and dynamic change process were obtained.
Fishes are at the top of the aquatic food chain, are the best indicators of the health status of aquatic ecosystems and are the organisms most sensitive to changes in the aquatic ecological environment. Given the shortcomings of the commonly used river physical habitat models that only consider hydraulic factors, a two-dimensional (2D) eco-hydrodynamic model, containing eco-hydrological elements, was constructed using the identified driving forces of the ecological evolution of rivers. The main hydrological elements are water depth and flow velocity, while the main ecological elements are NH3-N, chemical oxygen demand, and sediments. Based on field survey data, relevant studies, and a comprehensive analysis of the natural geographical characteristics of the Luanhe River Basin, the dominant fish and plant species in the study area (the river section from the Daheiting-Taolinkou Reservoir to Luanxian Hydrological Station) were determined to be Cypriniformes and reed, respectively. The habitat suitability indices (HSIs) of various target species were determined using the model simulation method and the observational statistical method, and the river habitat quality model was constructed based on the 2D eco-hydrodynamic model. The spatial distribution and dynamic change process of the habitat quality of carp in the Qianxi section downstream of the Daheiting Reservoir and reed in the Qianxi section of the Luanhe River were obtained by calculation. Comparison with existing studies and ecological monitoring data shows that the model proposed in this paper is reliable and effective, which will help with the development of ecological protection and management efforts for rivers with not enough ecological monitoring data.
Compared with conventional pumped-storage hydroplants, seawater pumped-storage hydroplants are constructed in a complex marine environment. The wave disturbance may affect the safety operation of the ...pump turbine in the seawater pumped hydroplant via affecting the level of the free water surface. To explore the effect of wave disturbance on the operation of the pump turbine in a seawater pumped-storage hydroplant, assuming that the wave disturbance follows a sine function, on the basis of Airy’s micro-amplitude wave theory and the comprehensive characteristic curve of a pump turbine, we use sliding grid technology and the SST
k
–
ω
turbulence model to simulate the dynamics of fluid in a full-flow channel. In this study, the unsteady flow field,
Q
-criterion vorticity, relative pressure pulsation amplitude, and frequency of pressure pulsation are analyzed to determine the internal flow field and pressure pulsation under different wave disturbance conditions and operating loads. The results show that both the pressure pulsation in the pump turbine and its frequency domain are affected by the wave disturbance. In addition, the turbulent flow with a large flow rate tends to produce higher relative pressure pulsation under wave disturbance. Due to the large flow rate and strong static and dynamic interference in the vaneless area, the relative amplitude of the pressure pulsation is significantly affected by wave disturbance. Furthermore, the low-frequency pressure pulsation of the draft tube is superimposed with the wave disturbance frequency.
Abstract
A hydraulic-stepped spillway was designed using an aeration basin to provide aerated flow to the stepped spillway utilizing a hydraulic jump. However, the flow through the entrance of the ...stepped spillway might separate from the first step top and impact the downstream steps at a large unit discharge, causing a so-called jet flow. A new experimental study was conducted to better understand the jet flow in the hydraulic-jump-stepped spillway with comparisons with conventional stepped spillways. The results showed that the critical condition required for the formation of the jet flow was close to the geometric parameters of the upstream aeration basin. Among these parameters, the height of the reverse step had a more significant effect on the local flow pattern, thus lowering the risk of jet flow. The relationships between the critical condition and the geometry of the aeration basin suggested that the Froude number at the entrance of the stepped spillway was the key parameter forming the jet flow. Compared with conventional stepped spillways, the hydraulic-jump-stepped spillway could effectively extend the practical application for large unit discharges by providing a better understanding of jet flow conditions.
Downstream of the sluice gate or weir, wave-type flows inevitably occur in stilling basins with no tailwater. This paper aims to investigate the hydraulic performance of wave-type flows at a ...sill-controlled stilling basin through experimental research. The flow pattern, bottom pressure profiles along the stilling basin, and the air concentrations on the bottom and the sidewall were examined in five sill-controlled stilling basins by altering the sill position and the height. The results show that wave-type flow patterns contain submerged and non-submerged jumps, which are relevant to ambient pressure head and air entrainment. The bottom pressure profiles are related to larger pressure fluctuations at large unit discharges and two peak pressure values in the vicinity of the sill. The air concentrations on the bottom and the sidewall decrease with the increasing unit discharge. The flow zone in the vicinity of the sill should be focused upon concerning protection against cavitation damage because of the slight air entrainment and significant pressure fluctuations. These findings advance our understanding of wave-type flows, and their ambient pressure heads and air entrainment are useful for designing the sill-controlled stilling basin in hydraulic engineering.
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