bluuebunny/crossref_metadata_2025_split huggingface dataset:
Noise analysis and optical response of microwave kinetic inductance detectors with an optical stack
Authors: Nicaise Paul , Hu Jie , Chaumont Christine , Bonifacio Piercarlo , Piat Michel , Geoffray Hervé , Boussaha Faouzi 
Published: June 2024

Abstract
We report on the experimental investigation of optical coupling for superconducting microresonators known as microwave kinetic inductance detectors (MKIDs) in the visible and near-infrared bands. MKIDs are photon-counting, time and energy-resolving detectors that still suffer from a poor quantum efficiency. To improve this efficiency, we propose to add a superconducting reflective layer below the absorbing part of the detector separated by a transparent Al2O3 layer with a quarter-wavelength thickness optimized around a single wavelength λ = 405 nm. We have first fabricated samples patterned from stoichiometric TiN (

T
c

∼
4

K), one with the full optical stack, one without for reference and one with a partial optical stack in order to characterize the noise influence of each layer individually. We observe that the full optical stack geometry has the most impact on the resonator’s noise and quality factors. A second design was fabricated to characterize the optical response to short pulses of the optical stack and we show from both the frequential noise and optical response that a strong signature of TLS is still present in the optical stack sample. We have finally obtained single-photon response with the optical stack using a more sensitive tri-layer TiN/Ti/TiN absorber (

T
c

∼
1.3

K) for which a maximum energy resolving power of

R
=
E

/

Δ
E
∼

1.3 was achieved using 405 nm laser pulses at 225 mK. The quality factors of both the reference and optical stack samples are similar but the frequency noise is still a tenfold higher for the optical stack sample which degrades the energy-resolving power of the detector.
Development of a multi-pancake HTS magnet operated in persistent current mode based on superconducting joint of REBCO coated conductors
Authors: Huang Daxing , Dong Hao , Wang Tongxin , Gu Hongwei , Ding Fazhu 
Published: June 2024

Abstract
Developing closed-loop magnets that operate in a persistent current mode (PCM) is crucial for achieving higher resolution and sensitivity in NMR and MRI devices. To the best of our knowledge, we report a novel closed-loop multi-pancake (MP) HTS magnet operated on PCM based on a novel jointless winding method with superconducting joints of REBCO coated conductors (CCs). The in-field characteristics of the CC and the joints were investigated to determine the operating parameters of the magnet. The steady central field of the magnet reached ∼408.4 mT at 77 K with an operating current of 16.5 A. The joint resistance was inferred from a higher excitation current of 17 A to be at least less than 2.5 × 10−10Ω. Although the I
c value of the joint was considerably lower than that of the CC at self-field, it could maintain similar comparable or even higher in-field I
c compared to the CC, which is immensely beneficial for magnet applications. This study provides some insights into the design and construction of closed-loop MP magnets operating in PCM.
Connecting quantum cities: simulation of a satellite-based quantum network
Authors: Yehia Raja , Schiavon Matteo , Marulanda Acosta Valentina , Coopmans Tim , Kerenidis Iordanis , Elkouss David , Diamanti Eleni 
Published: June 2024

Abstract
We present and analyze an architecture for a European-scale quantum network using satellite links to connect Quantum Cities, which are metropolitan quantum networks with minimal hardware requirements for the end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess and benchmark the performance of such a network linking distant locations in Europe in terms of quantum key distribution rates, considering realistic parameters for currently available or near-term technology. Our results highlight the key parameters and the limits of current satellite quantum communication links and can be used to assist the design of future missions. We also discuss the possibility of using high-altitude balloons as an alternative to satellites.
Velocity selective multiple two-photon dark and bright resonances in Potassium vapor
Authors: Pal Gourab , Dutta Gupta Subhasish , Chaudhuri Saptarishi 
Published: June 2024

Abstract
We report the observation of two additional sub-natural line width quantum interferences in the D
2 manifold of 39
K vapor, in addition to the usual single Electromagnetically Induced Transparency (EIT) peak. In a typical three level Λ-type system, only one EIT peak is observed. However, here we report observation of two additional line shapes riding on top of the absorption profile. The fact that the hyperfine splitting is smaller than the Doppler width in 39
K allows the probe and control beams to swap their transition pathways in different velocity groups of atoms even when their frequencies are kept constant. Our observations are in striking contrast to standard EIT measurements. These findings are in quantitative agreement with density matrix formalism taking into account velocity-selective two-photon resonances. Owing to the favorably low ground hyperfine splitting (Δ
hf
) in 39
K, which allows a significantly large number of atoms with a Doppler shift greater than or equal to the Δ
hf
, the strength of these additional resonances is strong compared to that of other alkali atoms such as 87
Rb, 133
Cs where these resonances can not be observed. The control photon detuning to atomic transition captures the nature of the coherence; therefore an unusual phenomenon of conversion from perfect transparency to enhanced absorption of the probe photon is observed and explained by utilizing the adiabatic elimination of the excited state in the Master equation. Controlling such dark and bright resonances leads to new applications in quantum technologies such as frequency-offset laser stabilization and long-lived quantum memory.
The PTA Hellings and Downs correlation unmasked by symmetries
Authors: Kehagias A. , Riotto A. 
Published: June 2024

Abstract
The Hellings and Downs correlation curve describes
the correlation of the timing residuals from pairs of pulsars as a function of their angular separation on the sky and is
a smoking-gun signature for the detection of an isotropic stochastic background of gravitational waves. We show that it can be easily obtained from
realizing that Lorentz transformations are conformal transformations
on the celestial sphere and from the conformal properties of the two-point correlation of the timing residuals. This result allows several generalizations, e.g. the calculation of the three-point correlator of the time residuals and the inclusion of additional polarization modes (vector and/or scalar) arising in alternative
theories of gravity.
Beta-band power classification of go/no-go arm-reaching responses in the human hippocampus
Authors: Martin del Campo Vera Roberto , Sundaram Shivani , Lee Richard , Lee Yelim , Leonor Andrea , Chung Ryan S , Shao Arthur , Cavaleri Jonathon , Gilbert Zachary D , Zhang Selena , Kammen Alexandra , Mason Xenos , Heck Christi , Liu Charles Y , Kellis Spencer , Lee Brian 
Published: June 2024

Abstract

Objective. Can we classify movement execution and inhibition from hippocampal oscillations during arm-reaching tasks? Traditionally associated with memory encoding, spatial navigation, and motor sequence consolidation, the hippocampus has come under scrutiny for its potential role in movement processing. Stereotactic electroencephalography (SEEG) has provided a unique opportunity to study the neurophysiology of the human hippocampus during motor tasks. In this study, we assess the accuracy of discriminant functions, in combination with principal component analysis (PCA), in classifying between ‘Go’ and ‘No-go’ trials in a Go/No-go arm-reaching task. Approach. Our approach centers on capturing the modulation of beta-band (13–30 Hz) power from multiple SEEG contacts in the hippocampus and minimizing the dimensional complexity of channels and frequency bins. This study utilizes SEEG data from the human hippocampus of 10 participants diagnosed with epilepsy. Spectral power was computed during a ‘center-out’ Go/No-go arm-reaching task, where participants reached or withheld their hand based on a colored cue. PCA was used to reduce data dimension and isolate the highest-variance components within the beta band. The Silhouette score was employed to measure the quality of clustering between ‘Go’ and ‘No-go’ trials. The accuracy of five different discriminant functions was evaluated using cross-validation. Main results. The Diagonal-Quadratic model performed best of the 5 classification models, exhibiting the lowest error rate in all participants (median: 9.91%, average: 14.67%). PCA showed that the first two principal components collectively accounted for 54.83% of the total variance explained on average across all participants, ranging from 36.92% to 81.25% among participants. Significance. This study shows that PCA paired with a Diagonal-Quadratic model can be an effective method for classifying between Go/No-go trials from beta-band power in the hippocampus during arm-reaching responses. This emphasizes the significance of hippocampal beta-power modulation in motor control, unveiling its potential implications for brain–computer interface applications.
The setting criterion of the downstream surge chamber for pumped storage power station
Authors: Wang Jue , Ding Jinghuan , Han Wenfu , Zhao Long , Du Kenan 
Published: June 2024

Abstract
This paper aims to explore and overcome the limitation of the existing criterion of downstream surge chamber without considering the influence of the head loss in the long waterway system, and deduce the change process of the flow with time (opening) of the unit. On this basis, the setting criterion of downstream surge chamber is derived, which takes into account the water hammer vacuum caused by water inertia in the tailwater system, the velocity head vacuum at the inlet of the draft tube and the friction vacuum of the water delivery system, and the mathematical model of the limit length of the tailwater system is established. The criterion presented in this paper can be used as a preliminary criterion to determine whether the downstream surge chamber is set up or not, and can provide reference for the preliminary design of similar projects in the early stage.
Numerical Investigation of Wake Properties of a Propeller Using Immersed Boundary Method
Authors: Li Haoyu , Kan Kan 
Published: June 2024

Abstract
A level-set based sharp-interface immersed boundary method (IBM) was applied with large eddy simulation to simulate the complex flow field around a marine propeller. The wake characteristics under the open-water conditions including velocity, pressure and turbulent kinetic energy were analyzed. Additionally, the comparative analysis of the axial Reynolds stress of the propeller operating beneath incident waves and that under the open-water condition indicates that the nonlinear interaction between waves and wake leads to the increase in Reynolds stress within the radial range of r/D=0.35 to r/D=0.55 in the far-wake region. The obtained numerical simulation results confirmed the feasibility of the IBM for the numerical simulation of complex flows through hydraulic machinery such as propellers.
Numerical Investigation of Performance and Flow Characteristics of Francis Turbine in Part Load Condition
Authors: Umar Baig Mirza , Huang Xingxing 
Published: June 2024

Abstract
Due to the complexity of the flow phenomena inside Francis turbines, it is very time-consuming and expensive to determine their performance and flow characteristics under different operating conditions through model tests and field measurements. The use of computational fluid dynamics (CFD) to improve turbine design and performance is a more cost-effective alternative to traditional methods of forecasting flow characteristics in different flow domains across the whole turbine channel. The performance and flow characteristics of the turbine under various part load working circumstances are studied by numerical simulations employing the shear stress transfer SST (k − ω) turbulence model. Four different operating conditions from 50%,70%,80% and 100% of the maximum and minimum power were analyzed, and the flow characteristics across the entire turbine channel were investigated in detail. The study results shows the calculated efficiencies of four operating condition have good agreement with measured ones, and the efficiency differences between numerical simulation and measurement are below 0.44%. Visualization of velocity and pressure in the whole Francis turbine shows that output torque, output power, and performance are in good agreement with experiment results. This study’s findings can be utilized to improve the design, efficiency, and hydraulic stability of Francis turbines.
Stability analysis of hydropower unit operation conditions considering hydro-turbine nonlinearity
Authors: Lu Xueding , Li Chaoshun 
Published: June 2024

AbstractThis paper aims to study the law that the stability of hydropower systems changes with the system operating point and clarify the impact of hydro-turbine nonlinearity and hydraulic nonlinearity on the system stability. Firstly, the piecewise linearized model of the hydro-turbine regulation system (HTRS) at various operating points is established. Then, the HTRS stability domain is calculated and analyzed under various working heads and guide vane openings, and the impact of head variation on system stability is researched from the perspectives of discharge and power. Finally, the stability of various operating conditions under ideal hydro-turbine conditions and rated hydraulic parameter conditions are and compared to clarify the role of the water system and turbine nonlinearity on the stability. The results show that hydro-turbine nonlinearity helps to improve the system stability of the overall operating conditions, but the stability of the HTRS is relatively weak during high-load and low-head operations. Moreover, the hydro-turbine nonlinearity plays a dominant role in the process of stability changing with the operating head. This paper provides a comprehensive analysis of the system stability at different operating points, which can help guide the control optimization of hydropower systems.
Analysis of the impact of Tibet Plateau environment on the operating conditions of water turbine machine
Authors: Luo Hongying , Xie Jiuming , Liang Quanwei , Wang Zhengwei 
Published: June 2024

Abstract
Tibet has rich water conservancy resources, and the focus of hydropower development has gradually shifted to Tibet. The primary condition for the stable operation of the water turbine is to satisfy and adapt to the environment. On the basis of investigating the environmental characteristics of the Tibet Plateau, this paper analyzes the impact of its harsh conditions such as altitude, temperature, air density, and sediment. The results show that with the elevation increasing, the minimum inlet pressure of draft tube should be used as elevation correction, and the cavitation volume shows the maximum value at 20°C, and the cavitation velocity decreases when it is larger than 20°C, the decrease of air density makes it difficult to use air convection as the main cooling equipment. The problem found during the maintenance process are analyzed, and the research look forward to providing relevant data and basic technical support for the development of Water resources in Tibet.
Experimental study on draft tube of a model kaplan turbine
Authors: Xu Lianchen , Kan Kan , Zheng Yuan , Liu Demin 
Published: June 2024

Abstract
To obtain the flow characteristics inside the draft tube of the model Kaplan turbine, a model test method was developed and carried out in this paper. The method includes introducing the model test system, test method, and parameters of model Kaplan turbine. Subsequently, experiments are conducted under different operating conditions and the results are analyzed. The result shows that, for the same blade angle and unit speed, operating conditions with larger guide vane openings (GVO) generally have higher axial velocities and lower tangential velocities than those with smaller GVO. In addition, particularly at higher flow velocities, a low velocity or backflow zone can occur in the center of the draft tube. Vortex rope is found to have a significant impact on the turbulence intensity in the mid-section of the draft tube, resulting in an unstable flow state. Also, under higher unit speed operating conditions, the turbulence intensity in the middle of the measurement area is greater and has a larger sphere of influence. Finally, the tangential pulsation intensity at the same measuring point under the same operating conditions is larger than the axial pulsation intensity, showing that vortex ropes have a more significant influence in the tangential direction.
Data-model Interactive Health Condition Assessment for Hydropower Unit
Authors: Liu Yujie , Liu Jie , Zhang Fengyuan , Gao Hua , Li Yuxin , Yuan Xiaohui 
Published: June 2024

Abstract
The health condition assessment (HCA) of hydropower unit plays an important role in enhancing safe operation of hydropower stations and reducing maintenance costs. Due to the harsh environment, there are some problems of sensor data during the unit operations, including abnormal data, missing data and high-noise data. Also, it is difficult to obtain complete monitoring data during run-to-failure maintenance. These issues definitely cause the low-confidence HCA. Thus, a data-model-interactive HCA for hydropower unit was proposed. First, a high-fidelity 3D mechanism simulation model, interacting with the actual unit, was built using unit drawing data provided by manufacturers. Average values of the volute inlet pressure and draft tube outlet pressure were fed into the dynamics simulation model to obtain the simulated pressure pulsation data under working conditions (water head H and power P). Then, a long short-term memory based healthy condition model was constructed using the power parameters, simulation and normal pressure pulsation. After model construction, difference values between simulated pressure pulsation dataset and degradation state pressure pulsation dataset were calculated to build the performance degradation index (PDI), describing the HCA of units. Finally, the PDI was fed into the convolutional neural networks and long short-term memory model to achieve degradation trend prediction. Validation experiment was conducted to verify the effectiveness of proposed method using actual monitoring data and operating parameters of 6# unit in the hydropower station.
Effect of uneven inflow on hydrodynamic performance of bulb turbine
Authors: Liu H , Cheng Y G , Yang Z Y , Zhang J , Fan J Y , Li W X 
Published: June 2024

Abstract
Bulb turbine unit is characterized by its low head, large discharge, and short flow passage. The guiding wall separating the power house section from the flood discharge section may cause uneven inflow before its neighbor units when the power house section is located off the river’s mainstream. In this study, selecting a bulb turbine hydropower station in China as the subject, we establish a three-dimensional CFD model that contains the full flow passage of the turbine unit and partial upstream reservoir, to analyze the effects of uneven inflow on the hydrodynamic performance of the bulb turbine. The results show that under this power station layout, flow separation occurs on the left side of the guiding wall, resulting in a low pressure zone and causing the flow in a three-dimensional vortical pattern. The low pressure and flow energy loss lead to the reduction of the neighbor units’ head, causing the discharge decreasing, and the output cannot reach the expectations. This situation can be improved by shortening the guiding wall, indicating that the unit’s performance is strongly related to the hydraulic structure arrangement. The results can provide some references for the design and operation of the related project.
Experimental analysis of the pressure fluctuations for a prototype pump-turbine at different operating conditions
Authors: Guo Bao , Yu Ran , Ye Ye , Li Xiushu , Xiao Yexiang 
Published: June 2024

Abstract
The pressure fluctuations are one of the crucial instabilities detrimental to the stable operation of pump turbines. The fluctuations are periodic and stochastic. They naturally exist in all kinds of operating conditions and cannot be eliminated. Many studies have been conducted on the pressure fluctuations for pump-turbines. However, detailed analysis of the characteristics of the prototypes is relatively rare and needs further investigation. In this study, six pressure sensors from the spiral inlet to the draft tube outlet have been mounted on a prototype pump-turbine. The recorded pressure values for these sensors were analysed at four different operating conditions from 25% to 100% of BEP (Best efficiency point) loads. Results show the relative fluctuations of vaneless space is only 2.8% at BEP load, showing the prototype operation is stable at the rated power. However, for off-design conditions, the amplitude of dominant frequencies is greatly enhanced. The amplitude is about 18 times at 25% loads compared to that at the BEP load. In addition, the dominant frequencies in the draft tube inlet are characterized by low-frequency components originating from the vortex rope. The current work provides a preliminary understanding of the instability in a prototype pump-turbine and can be used as a reference to minimize the negative effects of pressure fluctuations.
A review of the experimental techniques research progress of the Pelton turbine
Authors: Zhonghua Gui , Yexiang Xiao , Dongkuo Li , Hao Lin , Wei Xiao , Yilin Zhu 
Published: June 2024

Abstract
The Pelton turbine internal flow is by far the most complex of all hydraulic turbo-machinery, which consists of confined flow, free jet flow, free-surface water sheet flow and dispersed flow. The efficiency of Pelton turbine is closely related to these flow phenomena, thus knowing the dynamic behaviour of these flow patterns is of high interest to the optimization of Pelton turbine hydraulic flow parts. The experimental techniques were used to analyse the relationship between the connect of the turbine performance and flow patterns for the earlier researches. The present paper reviewed the development of experimental techniques of Pelton turbines, summarized the emerging test means and discussed the internal flow mechanism.
The model test research of medium-low specific speed Francis pump-turbine
Authors: Guo Y F , Guo Q B , Liu Z L 
Published: June 2024

Abstract
In the last few years, the pumped storage power station grows vigorously. As a result, the higher demand have been put forward in relevant technical fields. This article mainly discusses the model test research of medium-low specific speed Francis pump-turbine. Furthermore, the pump-turbine model test method of performance, cavitation, pressure pulsation, complex characteristics, and the rest auxiliary test is expounded and studied, with a view to optimizing pump-turbine model test method and further improving test rate. It can provide the favorable condition for the pump-turbine unit design and power station continuously operation.