SU\G(𝔸)/K·U
Sign Up for free Log In

Author Description

Login to generate an author description

Ask a Question About This Mathematician

CEPC Conceptual Design Report: Volume 2 - Physics & Detector

2018-01-01
J. Barreiro Guimarães da Costa , J. Qian , C. Tully +7 more
The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the … The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the underlying fundamental physics principles of the Standard Model that might reveal new physics. The CEPC, to be hosted in China in a circular underground tunnel of approximately 100 km in circumference, is designed to operate as a Higgs factory producing electron-positron collisions with a center-of-mass energy of 240 GeV. The collider will also operate at around 91.2 GeV, as a Z factory, and at the WW production threshold (around 160 GeV). The CEPC will produce close to one trillion Z bosons, 100 million W bosons and over one million Higgs bosons. The vast amount of bottom quarks, charm quarks and tau-leptons produced in the decays of the Z bosons also makes the CEPC an effective B-factory and tau-charm factory. The CEPC will have two interaction points where two large detectors will be located. This document is the second volume of the CEPC Conceptual Design Report (CDR). It presents the physics case for the CEPC, describes conceptual designs of possible detectors and their technological options, highlights the expected detector and physics performance, and discusses future plans for detector R&D and physics investigations. The final CEPC detectors will be proposed and built by international collaborations but they are likely to be composed of the detector technologies included in the conceptual designs described in this document. A separate volume, Volume I, recently released, describes the design of the CEPC accelerator complex, its associated civil engineering, and strategic alternative scenarios.
View PDF Chat

Unconventional superconducting phase in the weakly correlated noncentrosymmetric<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Mo</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>Al</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mtext>C</mml:mtext></mml:mrow></mml:math>compound

2010-08-17
E. Bauer , Gerda Rogl , Xing‐Qiu Chen +7 more
Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ ($\ensuremath{\beta}\text{-Mn}$ type, space group $P{4}_{1}32$) as a strong-coupled superconductor with ${T}_{c}=9\text{ }\text{K}$ deviating notably from BCS-type behavior. The absence of a … Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ ($\ensuremath{\beta}\text{-Mn}$ type, space group $P{4}_{1}32$) as a strong-coupled superconductor with ${T}_{c}=9\text{ }\text{K}$ deviating notably from BCS-type behavior. The absence of a Hebbel-Slichter peak, a power-law behavior of the spin-lattice relaxation rate (from $^{27}\text{A}\text{l}$ NMR), an electronic specific heat strongly deviating from BCS model and a pressure enhanced ${T}_{c}$ suggest unconventional superconductivity with possibly a nodal structure of the superconducting gap. Relativistic density-functional theory calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favoring a mix of spin-singlet and spin-triplet components in the superconducting condensate, in absence of strong correlations among electrons.
View PDF Chat

I-mode investigation on the Experimental Advanced Superconducting Tokamak

2019-06-11
Xi Feng , A. D. Liu , C. Zhou +7 more
By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak.During the L-mode to I-mode transition, the energy … By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak.During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode.Similar with the I-mode observation on other devices, the E r profiles obtained by the eight-channel Doppler backscattering system (DBS8) [1] show a deeper edge E r well in the I-mode than that in the L-mode.And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm.WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the E r fluctuation and the caused flow shear from WCM should play an important role during I-mode.In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared.Many evidences show that the a low-frequency oscillation may be a
View PDF Chat

CEPC Technical Design Report: Accelerator

2024-03-01
Waleed Abdallah , K. Afanaciev , Shakeel Ahmad +7 more
View PDF Chat

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

2022-05-20
Yuejiang Shi , Bing Liu , Shaodong Song +7 more
Abstract As a new spherical tokamak designed to simplify the engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio vacuum vessel (VV), … Abstract As a new spherical tokamak designed to simplify the engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard x-ray detectors, carry the bulk of the plasma current ranging from 50–150 kA, which is maintained for more than 1 s duration. It is observed that over one ampere current can be sustained per watt of ECRH power issued from the 28 GHz gyrotrons. The plasma current reaches I p &gt; 80 kA for high density (&gt;5 × 10 18 m −2 ) discharge with 150 kW ECRH. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates a smaller closed magnetic-flux surface of low aspect ratio that in turn confines the thermal plasma electrons and ions and participate in maintaining the equilibrium force balance.
View PDF Chat

Distributed Reinforcement Learning for Decentralized Linear Quadratic Control: A Derivative-Free Policy Optimization Approach

2019-01-01
Yingying Li , Yujie Tang , Runyu Zhang +1 more
This paper considers a distributed reinforcement learning problem for decentralized linear quadratic control with partial state observations and local costs. We propose a Zero-Order Distributed Policy Optimization algorithm (ZODPO) that … This paper considers a distributed reinforcement learning problem for decentralized linear quadratic control with partial state observations and local costs. We propose a Zero-Order Distributed Policy Optimization algorithm (ZODPO) that learns linear local controllers in a distributed fashion, leveraging the ideas of policy gradient, zero-order optimization and consensus algorithms. In ZODPO, each agent estimates the global cost by consensus, and then conducts local policy gradient in parallel based on zero-order gradient estimation. ZODPO only requires limited communication and storage even in large-scale systems. Further, we investigate the nonasymptotic performance of ZODPO and show that the sample complexity to approach a stationary point is polynomial with the error tolerance's inverse and the problem dimensions, demonstrating the scalability of ZODPO. We also show that the controllers generated throughout ZODPO are stabilizing controllers with high probability. Lastly, we numerically test ZODPO on multi-zone HVAC systems.
View PDF Chat

Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Mg</mml:mi></mml:mrow><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>22</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi>p</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:mmultiscripts><mml:…

2021-10-19
Jun Hu , H. Yamaguchi , Y. H. Lam +7 more
We report the first (in)elastic scattering measurement of ^{25}Al+p with the capability to select and measure in a broad energy range the proton resonances in ^{26}Si contributing to the ^{22}Mg(α,p) … We report the first (in)elastic scattering measurement of ^{25}Al+p with the capability to select and measure in a broad energy range the proton resonances in ^{26}Si contributing to the ^{22}Mg(α,p) reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the α threshold of ^{26}Si that are found to strongly impact the ^{22}Mg(α,p) rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS 1826-24 clocked burster with mean deviation <9% and permits us to discover a strong correlation between the He abundance in the accreting envelope of the photospheric radius expansion burster and the dominance of ^{22}Mg(α,p) branch.
View PDF Chat

Safe Adaptive Learning-based Control for Constrained Linear Quadratic Regulators with Regret Guarantees

2021-01-01
Yingying Li , Subhro Das , Jeff S. Shamma +1 more
We study the adaptive control of an unknown linear system with a quadratic cost function subject to safety constraints on both the states and actions. The challenges of this problem … We study the adaptive control of an unknown linear system with a quadratic cost function subject to safety constraints on both the states and actions. The challenges of this problem arise from the tension among safety, exploration, performance, and computation. To address these challenges, we propose a polynomial-time algorithm that guarantees feasibility and constraint satisfaction with high probability under proper conditions. Our algorithm is implemented on a single trajectory and does not require system restarts. Further, we analyze the regret of our learning algorithm compared to the optimal safe linear controller with known model information. The proposed algorithm can achieve a $\tilde O(T^{2/3})$ regret, where $T$ is the number of stages and $\tilde O(\cdot)$ absorbs some logarithmic terms of $T$.
View PDF Chat

Experimental study of the characteristics of energetic electrons outside LCFS in EXL-50 spherical torus

2022-03-02
Dong Guo , Yuejiang Shi , Wenjun Liu +7 more
Abstract Significant number of confined energetic electrons have been observed outside of the LCFS (last-closed flux surface) of EXL-50’s solenoid-free electron cyclotron resonance heating (ECRH) sustained plasmas. Several measurement technologies … Abstract Significant number of confined energetic electrons have been observed outside of the LCFS (last-closed flux surface) of EXL-50’s solenoid-free electron cyclotron resonance heating (ECRH) sustained plasmas. Several measurement technologies have been applied to verify the key characteristics of energetic electrons for the first time. Experiments reveal that the presence of high-temperature, low-density electrons can carry relatively large quantities of the stored energy. The boundary between the thermal plasma and the energetic fluid is clearly separated and the distance between the two boundaries can reach tens of centimeters (around the size of the minor radius of the thermal plasma). This implies that the Grad-Shafranov equilibrium is not adequate to describe the equilibrium of EXL-50 plasma and a multi-fluid model is required. Particle simulations of full orbits show that energetic electrons can be well confined outside the LCFS. This is consistent with the experimental observations.
View PDF Chat

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

2021-05-10
Yuejiang Shi , Bing Liu , Shaodong Song +7 more
Abstract As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel … Abstract As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to possibly improve current drive effectiveness. The energetic electrons are observed via hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current with high line-density (approaching 1019m-2) has been achieved for plasma currents as high as 76kA. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.
View PDF Chat

Probing the local electronic structure of isovalent Bi atoms in InP

2020-01-31
C. M. Krammel , Adonai Rodrigues da Cruz , Michael E. Flatté +7 more
Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. We map the spatial pattern of the Bi … Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. We map the spatial pattern of the Bi impurity state, which originates from Bi atoms down to the sixth layer below the surface, in topographic, filled-state X-STM images on the natural ${110}$ cleavage planes. The Bi impurity state has a highly anisotropic bowtielike structure and extends over several lattice sites. These Bi-induced charge redistributions extend along the $\ensuremath{\langle}110\ensuremath{\rangle}$ directions, which define the bowtielike structures we observe. Local tight-binding calculations reproduce the experimentally observed spatial structure of the Bi impurity state. In addition, the influence of the Bi atoms on the electronic structure is investigated in scanning tunneling spectroscopy measurements. These measurements show that Bi induces a resonant state in the valence band, which shifts the band edge toward higher energies. Furthermore, we show that the energetic position of the Bi-induced resonance and its influence on the onset of the valence band edge depend crucially on the position of the Bi atoms relative to the cleavage plane.
View PDF Chat

Non-asymptotic System Identification for Linear Systems with Nonlinear Policies

2023-01-01
Yingying Li , Tianpeng Zhang , Subhro Das +2 more
This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control … This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control for constrained linear systems, where the safe policies during the learning process are usually nonlinear and time-varying for satisfying the state and input constraints. In this paper, we provide a non-asymptotic error bound for least square estimation when the data trajectory is generated by any nonlinear and/or time-varying policies as long as the generated state and action trajectories are bounded. This significantly generalizes the existing non-asymptotic guarantees for linear system identification, which usually consider i.i.d. random inputs or linear policies. Interestingly, our error bound is consistent with that for linear policies with respect to the dependence on the trajectory length, system dimensions, and excitation levels. Lastly, we demonstrate the applications of our results by safe learning with robust model predictive control and provide numerical analysis.
View PDF Chat

Low Mach number limit of strong solutions for 3-D full compressible MHD equations with Dirichlet boundary condition

2019-01-01
Lan Zeng , Guoxi Ni , Yingying Li
In this paper, we consider the low Mach number limit of the full compressible MHD equations in a 3-D bounded domain with Dirichlet boundary condition for velocity field, Neumann boundary … In this paper, we consider the low Mach number limit of the full compressible MHD equations in a 3-D bounded domain with Dirichlet boundary condition for velocity field, Neumann boundary condition for temperature and perfectly conducting boundary condition for magnetic field. First, the uniform estimates in the Mach number for the strong solutions are obtained in a short time interval, provided that the initial density and temperature are close to the constant states. Then, we prove the solutions of the full compressible MHD equations converge to the isentropic incompressible MHD equations as the Mach number tends to zero.

Learning the Uncertainty Sets for Control Dynamics via Set Membership: A Non-Asymptotic Analysis

2023-01-01
Yingying Li , Jing Yu , Lauren Conger +1 more
Set-membership estimation is commonly used in adaptive/learning-based control algorithms that require robustness over the model uncertainty sets, e.g., online robustly stabilizing control and robust adaptive model predictive control. Despite having … Set-membership estimation is commonly used in adaptive/learning-based control algorithms that require robustness over the model uncertainty sets, e.g., online robustly stabilizing control and robust adaptive model predictive control. Despite having broad applications, non-asymptotic estimation error bounds in the stochastic setting are limited. This paper provides such a non-asymptotic bound on the diameter of the uncertainty sets generated by set membership estimation on linear dynamical systems under bounded, i.i.d. disturbances. Further, this result is applied to robust adaptive model predictive control with uncertainty sets updated by set membership. We numerically demonstrate the performance of the robust adaptive controller, which rapidly approaches the performance of the offline optimal model predictive controller, in comparison with the control design based on least square estimation's confidence regions.
View PDF Chat

Neutrino magnetic dipole portal with low energy neutrino nucleus scattering data

2024-06-11
Yingying Li , Yufeng Li , Shuo-yu Xia
Sterile neutrinos that couple to the Standard Model via the neutrino magnetic dipole portals have been extensively studied at various experiments. In this work, we scrutinize these interactions for sterile … Sterile neutrinos that couple to the Standard Model via the neutrino magnetic dipole portals have been extensively studied at various experiments. In this work, we scrutinize these interactions for sterile neutrinos in the mass range of $\unit[0.1]{}-\unit[50]{MeV}$ through the nuclear and electron recoils at various neutrino scattering experiments. For the $e$-flavor specific dipole portal, we demonstrate that Dresden-II can provide leading constraints for $m_N \lesssim \unit[0.5]{MeV}$, setting aside currently unresolved theoretical uncertainties. For the $\mu$-flavor case, we show that the COHERENT experiment can probe a unique parameter region for $m_N$ in the range of $\unit[10]{}-\unit[40]{MeV}$ with the full dataset collected by the CsI[Na] scintillation detector, including both the energy and timing structure of the neutrino beam. We also present limits on the parameter regions of the $\tau$-flavor dipole portal using measurements of the solar neutrino flux from dark matter direct detection experiments.
View PDF Chat

First Identification of New X-Ray Spectra of Mo39+, Mo40+, W43+, W44+ and W45+ on EAST

2022-01-01
Fudi Wang , Dian Lu , Mingfeng Gu +7 more
New high-resolution x-ray spectra of Mo39+, Mo40+, W43+, W44+ and W45+ have been carefully confirmed for the first time by use of the x-ray imaging crystal spectrometer (XCS) in Experimental … New high-resolution x-ray spectra of Mo39+, Mo40+, W43+, W44+ and W45+ have been carefully confirmed for the first time by use of the x-ray imaging crystal spectrometer (XCS) in Experimental Advanced Superconducting Tokamak (EAST) under various combined auxiliary heating plasmas conditions. Wavelength of these new x-ray spectra is ranged from 3.895 {\AA} to 3.986 {\AA}. When core electron temperature (Te0) reaches 6.0 keV, Mo39+ and Mo40+ lines of 3.9727, 3.9294 and 3.9480 {\AA} can be effectively detected on XCS for EAST; meanwhile, line-integrated brightness of these spectral lines of Mo39+ and Mo40+ is very considerable when electron temperature reaches 12.9 keV. Multi-components spectral lines for W43+, W44+ and W45+ have also been identified when Te0 reaches 6 keV. Parts of spectral lines, such as Zn-1, Cu-2, Cu-4a, Cu-4d and Cu-5 lines of tungsten, are first observed experimentally. When electron temperature reaches 12.9 keV, line-integrated intensity for part of these spectral lines of W43+, W44+ and W45+ are considerable. These experimental results and theoretical predictions from FAC and FLYCHK codes are in good general agreement. These new spectral lines, obtained on XCS for EAST, are vital for deeply uncovering the mechanisms of ion and electron thermal, high-Z impurity and momentum (anomalous) transport to achieve the advanced steady-state operation scenarios for ITER and CFETR.

Observation of whistler wave instability driven by temperature anisotropy of energetic electrons on EXL-50 spherical torus

2023-01-01
Mingyuan Wang , Yuejiang Shi , Jiaqi Dong +7 more
Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to … Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to have multiple bands of frequencies proportional to the Alfv\'en velocity. This indicates that the observed mode frequencies satisfy the dispersion relation of whistler waves. In addition, suppression of the whistler waves by the synergistic effect of Lower Hybrid Wave (LHW) and ECW was also observed. This suggests that the whistler waves were driven by temperature anisotropy of energetic electrons. These are the first such observations (not runaway discharge) made in magnetically confined toroidal plasmas and may have important implications for studying wave-particle interactions, RF wave current driver, and runaway electron control in future fusion devices.

On the estimation of integrated covariance matrices of high dimensional diffusion processes

2012-03-01
Xinghua Zheng , Yingying Li
We consider the estimation of integrated covariance (ICV) matrices of high dimensional diffusion processes based on high frequency observations. We start by studying the most commonly used estimator, the realized … We consider the estimation of integrated covariance (ICV) matrices of high dimensional diffusion processes based on high frequency observations. We start by studying the most commonly used estimator, the realized covariance (RCV) matrix. We show that in the high dimensional case when the dimension $p$ and the observation frequency $n$ grow in the same rate, the limiting spectral distribution (LSD) of RCV depends on the covolatility process not only through the targeting ICV, but also on how the covolatility process varies in time. We establish a Mar\v{c}enko--Pastur type theorem for weighted sample covariance matrices, based on which we obtain a Mar\v{c}enko--Pastur type theorem for RCV for a class $\mathcal{C}$ of diffusion processes. The results explicitly demonstrate how the time variability of the covolatility process affects the LSD of RCV. We further propose an alternative estimator, the time-variation adjusted realized covariance (TVARCV) matrix. We show that for processes in class $\mathcal {C}$, the TVARCV possesses the desirable property that its LSD depends solely on that of the targeting ICV through the Mar\v{c}enko--Pastur equation, and hence, in particular, the TVARCV can be used to recover the empirical spectral distribution of the ICV by using existing algorithms.

Observation of a strong correlation between the positive floating potential near the edge and plasma current on EXL-50 ECW plasma

2021-01-01
Mingyuan Wang , Dong Guo , Xin Zhao +7 more
Fully non-inductive plasma current start-up without the central solenoid in ECW plasma was used on EXL-50 Spherical Torus with a weak external vertical field (Bv). Generally, the number of electrons … Fully non-inductive plasma current start-up without the central solenoid in ECW plasma was used on EXL-50 Spherical Torus with a weak external vertical field (Bv). Generally, the number of electrons leaving to the vessel wall by the gradient Bt is larger than ions, and the positive potential was built up in plasma. The relationship between floating potential and the plasma current was studied using the Langmuir probes near the boundary. The results show that the floating potential is positive (about 200V) and has a strong correlation with plasma current. In open magnetic field, the plasma current is driven by the high energy electrons in preferential confinement, the plasma current and potential approximately positively correlated with total electron density. After forming the closed flux surface, the plasma current consists mainly of the ECW driven current, and potential is negatively correlated with plasma current. By actively adjusting the Bv, it demonstrated that the positive voltage is approximately inversely correlated with the Bv and plasma current (Ip). Considering that the plasma temperature near the boundary is quite low (~eV), the positive voltage near the boundary caused by the high-energy electron loss. Therefore, the measurements of the boundary potential are important for the study of high-energy electron confinement performance, noninductive plasma current start-up and current driven.
View PDF Chat

Non-inductive plasma current sustainment with stochastic electron cyclotron in EXL-50 spherical torus

2021-01-01
Mingyuan Wang , Shikui Cheng , Bing Liu +7 more
The start-up and sustainment of a stochastic wave non-inductive current on a spherical torus was experimentally demonstrated for the first time using only electron cyclotron waves. The plasma current is … The start-up and sustainment of a stochastic wave non-inductive current on a spherical torus was experimentally demonstrated for the first time using only electron cyclotron waves. The plasma current is insensitive to the injection angle of ECWs and approximately linearly correlated with the slope of the X-ray spectrum. Its direction is determined by the vertical magnetic field (BV). The temporal development in the number of X-ray bremsstrahlung photons with a specified energy is consistent with the stochastic heating model. Moreover, the ratio of Amps to Watts of the ECW is generally &gt;1 kA/kW under normal conditions (maximum plasma current: 150 kA, ECW: 140 kW). The experimental results are explained using the stochastic heating model of the asymmetric electron velocity distribution in stochastic electromagnetic waves.

A Wasserstein distance-based spectral clustering method for transaction data analysis

2022-01-01
Yingqiu Zhu , Danyang Huang , Yingying Li +1 more
With the rapid development of online payment platforms, it is now possible to record massive transaction data. Clustering on transaction data significantly contributes to analyzing merchants' behavior patterns. This enables … With the rapid development of online payment platforms, it is now possible to record massive transaction data. Clustering on transaction data significantly contributes to analyzing merchants' behavior patterns. This enables payment platforms to provide differentiated services or implement risk management strategies. However, traditional methods exploit transactions by generating low-dimensional features, leading to inevitable information loss. In this study, we use the empirical cumulative distribution of transactions to characterize merchants. We adopt Wasserstein distance to measure the dissimilarity between any two merchants and propose the Wasserstein-distance-based spectral clustering (WSC) approach. Based on the similarities between merchants' transaction distributions, a graph of merchants is generated. Thus, we treat the clustering of merchants as a graph-cut problem and solve it under the framework of spectral clustering. To ensure feasibility of the proposed method on large-scale datasets with limited computational resources, we propose a subsampling method for WSC (SubWSC). The associated theoretical properties are investigated to verify the efficiency of the proposed approach. The simulations and empirical study demonstrate that the proposed method outperforms feature-based methods in finding behavior patterns of merchants.
View PDF Chat

Non-asymptotic System Identification for Linear Systems with Nonlinear Policies

2023-01-01
Yingying Li , Tianpeng Zhang , Subhro Das +2 more
This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control … This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control for constrained linear systems, where the safe policies during the learning process are usually nonlinear and time-varying for satisfying the state and input constraints. In this paper, we provide a non-asymptotic error bound for least square estimation when the data trajectory is generated by any nonlinear and/or time-varying policies as long as the generated state and action trajectories are bounded. This significantly generalizes the existing non-asymptotic guarantees for linear system identification, which usually consider i.i.d. random inputs or linear policies. Interestingly, our error bound is consistent with that for linear policies with respect to the dependence on the trajectory length, system dimensions, and excitation levels. Lastly, we demonstrate the applications of our results by safe learning with robust model predictive control and provide numerical analysis.
View PDF Chat

On the Convergence Rates of Set Membership Estimation of Linear Systems with Disturbances Bounded by General Convex Sets

2024-06-01
Haonan Xu , Yingying Li
This paper studies the uncertainty set estimation of system parameters of linear dynamical systems with bounded disturbances, which is motivated by robust (adaptive) constrained control. Departing from the confidence bounds … This paper studies the uncertainty set estimation of system parameters of linear dynamical systems with bounded disturbances, which is motivated by robust (adaptive) constrained control. Departing from the confidence bounds of least square estimation from the machine-learning literature, this paper focuses on a method commonly used in (robust constrained) control literature: set membership estimation (SME). SME tends to enjoy better empirical performance than LSE's confidence bounds when the system disturbances are bounded. However, the theoretical guarantees of SME are not fully addressed even for i.i.d. bounded disturbances. In the literature, SME's convergence has been proved for general convex supports of the disturbances, but SME's convergence rate assumes a special type of disturbance support: $l_\infty$ ball. The main contribution of this paper is relaxing the assumption on the disturbance support and establishing the convergence rates of SME for general convex supports, which closes the gap on the applicability of the convergence and convergence rates results. Numerical experiments on SME and LSE's confidence bounds are also provided for different disturbance supports.
View PDF Chat

Identification of Analytic Nonlinear Dynamical Systems with Non-asymptotic Guarantees

2024-11-01
Negin Musavi , Ziyao Guo , Geir E. Dullerud +1 more
This paper focuses on the system identification of an important class of nonlinear systems: linearly parameterized nonlinear systems, which enjoys wide applications in robotics and other mechanical systems. We consider … This paper focuses on the system identification of an important class of nonlinear systems: linearly parameterized nonlinear systems, which enjoys wide applications in robotics and other mechanical systems. We consider two system identification methods: least-squares estimation (LSE), which is a point estimation method; and set-membership estimation (SME), which estimates an uncertainty set that contains the true parameters. We provide non-asymptotic convergence rates for LSE and SME under i.i.d. control inputs and control policies with i.i.d. random perturbations, both of which are considered as non-active-exploration inputs. Compared with the counter-example based on piecewise-affine systems in the literature, the success of non-active exploration in our setting relies on a key assumption on the system dynamics: we require the system functions to be real-analytic. Our results, together with the piecewise-affine counter-example, reveal the importance of differentiability in nonlinear system identification through non-active exploration. Lastly, we numerically compare our theoretical bounds with the empirical performance of LSE and SME on a pendulum example and a quadrotor example.
View PDF Chat

An Efficient Diffusion-based Non-Autoregressive Solver for Traveling Salesman Problem

2025-01-23
Mingzhao Wang , You Zhou , Zhiguang Cao +7 more
Recent advances in neural models have shown considerable promise in solving Traveling Salesman Problems (TSPs) without relying on much hand-crafted engineering. However, while non-autoregressive (NAR) approaches benefit from faster inference … Recent advances in neural models have shown considerable promise in solving Traveling Salesman Problems (TSPs) without relying on much hand-crafted engineering. However, while non-autoregressive (NAR) approaches benefit from faster inference through parallelism, they typically deliver solutions of inferior quality compared to autoregressive ones. To enhance the solution quality while maintaining fast inference, we propose DEITSP, a diffusion model with efficient iterations tailored for TSP that operates in a NAR manner. Firstly, we introduce a one-step diffusion model that integrates the controlled discrete noise addition process with self-consistency enhancement, enabling optimal solution prediction through simultaneous denoising of multiple solutions. Secondly, we design a dual-modality graph transformer to bolster the extraction and fusion of features from node and edge modalities, while further accelerating the inference with fewer layers. Thirdly, we develop an efficient iterative strategy that alternates between adding and removing noise to improve exploration compared to previous diffusion methods. Additionally, we devise a scheduling framework to progressively refine the solution space by adjusting noise levels, facilitating a smooth search for optimal solutions. Extensive experiments on real-world and large-scale TSP instances demonstrate that DEITSP performs favorably against existing neural approaches in terms of solution quality, inference latency, and generalization ability. Our code is available at $\href{https://github.com/DEITSP/DEITSP}{https://github.com/DEITSP/DEITSP}$.
View PDF Chat

CP violation studies at Super Tau-Charm Facility

2025-02-12
Hai-Yang Cheng , Z. J. Guo , Xiao-Gang He +7 more
Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future … Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($\tau$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $\tau$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.
View PDF Chat

Promotional effect of calcination temperature on the Mn-Fe-Al based monolithic catalysts prepared by the low-cost materials for the acetone efficient degradation

2025-05-01
Yingying Li , Hang Xiao , Jian‐Rong Li

Suppression of continuous-wave-induced resonant sidebands in soliton molecule spectra

2025-05-11
Luyao Zhou , Lie Liu , Honglin Wen +5 more

Effect of 4.6 GHz LHW on tungsten transport in NBI dominant H-mode plasma in EAST tokamak

2025-05-16
Yunxin Cheng , Ling Zhang , Chengxi Zhou +7 more
Abstract Experimental observations in EAST tokamak have revealed a notable suppression of tungsten accumulation during the lower hybrid wave (LHW) injection in the neutral beam injection (NBI)-heated H-mode plasma. The … Abstract Experimental observations in EAST tokamak have revealed a notable suppression of tungsten accumulation during the lower hybrid wave (LHW) injection in the neutral beam injection (NBI)-heated H-mode plasma. The variation in tungsten concentration during the LHW phase is quantified using the intensity of tungsten unresolved transition array (W-UTA), as measured by the extreme ultraviolet (EUV) spectrometer. After the LHW is turned on, the tungsten concentration, CW=nW/ne, decreased by approximately 45%, from 9.5×10-5 to 5.3×10-5. Additionally, the peaked tungsten profile is flattened, with the peak position shifted outward, implying a significant alteration in tungsten transport. The observed results suggest that reduced toroidal rotation and increased electron temperature are responsible for the variation in tungsten transport during the LHW heating. Modeling using a simulation code of Transport in Gyrokinetic Plasmas with Rotation and Optimization (TGYRO) indicates that, after the LHW injection, the turbulent diffusion of tungsten ions is enhanced and the neoclassical convection is weakened. Moreover, comparisons of the transport coefficients of tungsten ions under different plasma parameters reveal that the LHW heating enhances the turbulent diffusion of tungsten ions by increasing the electron temperature gradient. It also decreases the plasma toroidal rotation velocity, which in turn reduces the inward neoclassical convection of tungsten ions. These findings provide a feasible solution for the tungsten accumulation induced by the NBI heating, supporting EAST in achieving long-pulse high-performance plasma discharge. This work offers an important reference for the operation of ITER and the design of future fusion reactors.

Effect of 4.6 GHz LHW on tungsten transport in NBI dominant H-mode plasma in EAST tokamak

2025-05-16
Yunxin Cheng , Ling Zhang , Chengxi Zhou +7 more
Abstract Experimental observations in EAST tokamak have revealed a notable suppression of tungsten accumulation during the lower hybrid wave (LHW) injection in the neutral beam injection (NBI)-heated H-mode plasma. The … Abstract Experimental observations in EAST tokamak have revealed a notable suppression of tungsten accumulation during the lower hybrid wave (LHW) injection in the neutral beam injection (NBI)-heated H-mode plasma. The variation in tungsten concentration during the LHW phase is quantified using the intensity of tungsten unresolved transition array (W-UTA), as measured by the extreme ultraviolet (EUV) spectrometer. After the LHW is turned on, the tungsten concentration, CW=nW/ne, decreased by approximately 45%, from 9.5×10-5 to 5.3×10-5. Additionally, the peaked tungsten profile is flattened, with the peak position shifted outward, implying a significant alteration in tungsten transport. The observed results suggest that reduced toroidal rotation and increased electron temperature are responsible for the variation in tungsten transport during the LHW heating. Modeling using a simulation code of Transport in Gyrokinetic Plasmas with Rotation and Optimization (TGYRO) indicates that, after the LHW injection, the turbulent diffusion of tungsten ions is enhanced and the neoclassical convection is weakened. Moreover, comparisons of the transport coefficients of tungsten ions under different plasma parameters reveal that the LHW heating enhances the turbulent diffusion of tungsten ions by increasing the electron temperature gradient. It also decreases the plasma toroidal rotation velocity, which in turn reduces the inward neoclassical convection of tungsten ions. These findings provide a feasible solution for the tungsten accumulation induced by the NBI heating, supporting EAST in achieving long-pulse high-performance plasma discharge. This work offers an important reference for the operation of ITER and the design of future fusion reactors.

Suppression of continuous-wave-induced resonant sidebands in soliton molecule spectra

2025-05-11
Luyao Zhou , Lie Liu , Honglin Wen +5 more

Promotional effect of calcination temperature on the Mn-Fe-Al based monolithic catalysts prepared by the low-cost materials for the acetone efficient degradation

2025-05-01
Yingying Li , Hang Xiao , Jian‐Rong Li

CP violation studies at Super Tau-Charm Facility

2025-02-12
Hai-Yang Cheng , Z. J. Guo , Xiao-Gang He +7 more
Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future … Charge-parity ($C\!P$) violation in the tau-charm energy region is a promising area for sensitive tests of Standard Model (SM) predictions and searches for new, beyond the SM physics. A future Tau-Charm Facility that operates at center-of-mass energies between 2.0 and 7.0 GeV, with a peak luminosity of $0.5\times10^{35}$~cm$^{-2}$s$^{-1}$, would provide huge numbers of hadrons and tau ($\tau$) leptons that are produced in low-background environments and with well understood kinematic properties. In this report, prospects for unique studies of $C\!P$ violation in the decay of charmed hadrons, and in the production and decay of hyperons and $\tau$ leptons at a next-generation tau-charm facility are discussed. In addition, opportunities for improved tests of $CPT$ invariance test in $K^{0}-\bar{K}^{0}$ mixing are presented.
View PDF Chat

An Efficient Diffusion-based Non-Autoregressive Solver for Traveling Salesman Problem

2025-01-23
Mingzhao Wang , You Zhou , Zhiguang Cao +7 more
Recent advances in neural models have shown considerable promise in solving Traveling Salesman Problems (TSPs) without relying on much hand-crafted engineering. However, while non-autoregressive (NAR) approaches benefit from faster inference … Recent advances in neural models have shown considerable promise in solving Traveling Salesman Problems (TSPs) without relying on much hand-crafted engineering. However, while non-autoregressive (NAR) approaches benefit from faster inference through parallelism, they typically deliver solutions of inferior quality compared to autoregressive ones. To enhance the solution quality while maintaining fast inference, we propose DEITSP, a diffusion model with efficient iterations tailored for TSP that operates in a NAR manner. Firstly, we introduce a one-step diffusion model that integrates the controlled discrete noise addition process with self-consistency enhancement, enabling optimal solution prediction through simultaneous denoising of multiple solutions. Secondly, we design a dual-modality graph transformer to bolster the extraction and fusion of features from node and edge modalities, while further accelerating the inference with fewer layers. Thirdly, we develop an efficient iterative strategy that alternates between adding and removing noise to improve exploration compared to previous diffusion methods. Additionally, we devise a scheduling framework to progressively refine the solution space by adjusting noise levels, facilitating a smooth search for optimal solutions. Extensive experiments on real-world and large-scale TSP instances demonstrate that DEITSP performs favorably against existing neural approaches in terms of solution quality, inference latency, and generalization ability. Our code is available at $\href{https://github.com/DEITSP/DEITSP}{https://github.com/DEITSP/DEITSP}$.
View PDF Chat

Identification of Analytic Nonlinear Dynamical Systems with Non-asymptotic Guarantees

2024-11-01
Negin Musavi , Ziyao Guo , Geir E. Dullerud +1 more
This paper focuses on the system identification of an important class of nonlinear systems: linearly parameterized nonlinear systems, which enjoys wide applications in robotics and other mechanical systems. We consider … This paper focuses on the system identification of an important class of nonlinear systems: linearly parameterized nonlinear systems, which enjoys wide applications in robotics and other mechanical systems. We consider two system identification methods: least-squares estimation (LSE), which is a point estimation method; and set-membership estimation (SME), which estimates an uncertainty set that contains the true parameters. We provide non-asymptotic convergence rates for LSE and SME under i.i.d. control inputs and control policies with i.i.d. random perturbations, both of which are considered as non-active-exploration inputs. Compared with the counter-example based on piecewise-affine systems in the literature, the success of non-active exploration in our setting relies on a key assumption on the system dynamics: we require the system functions to be real-analytic. Our results, together with the piecewise-affine counter-example, reveal the importance of differentiability in nonlinear system identification through non-active exploration. Lastly, we numerically compare our theoretical bounds with the empirical performance of LSE and SME on a pendulum example and a quadrotor example.
View PDF Chat

Neutrino magnetic dipole portal with low energy neutrino nucleus scattering data

2024-06-11
Yingying Li , Yufeng Li , Shuo-yu Xia
Sterile neutrinos that couple to the Standard Model via the neutrino magnetic dipole portals have been extensively studied at various experiments. In this work, we scrutinize these interactions for sterile … Sterile neutrinos that couple to the Standard Model via the neutrino magnetic dipole portals have been extensively studied at various experiments. In this work, we scrutinize these interactions for sterile neutrinos in the mass range of $\unit[0.1]{}-\unit[50]{MeV}$ through the nuclear and electron recoils at various neutrino scattering experiments. For the $e$-flavor specific dipole portal, we demonstrate that Dresden-II can provide leading constraints for $m_N \lesssim \unit[0.5]{MeV}$, setting aside currently unresolved theoretical uncertainties. For the $\mu$-flavor case, we show that the COHERENT experiment can probe a unique parameter region for $m_N$ in the range of $\unit[10]{}-\unit[40]{MeV}$ with the full dataset collected by the CsI[Na] scintillation detector, including both the energy and timing structure of the neutrino beam. We also present limits on the parameter regions of the $\tau$-flavor dipole portal using measurements of the solar neutrino flux from dark matter direct detection experiments.
View PDF Chat

On the Convergence Rates of Set Membership Estimation of Linear Systems with Disturbances Bounded by General Convex Sets

2024-06-01
Haonan Xu , Yingying Li
This paper studies the uncertainty set estimation of system parameters of linear dynamical systems with bounded disturbances, which is motivated by robust (adaptive) constrained control. Departing from the confidence bounds … This paper studies the uncertainty set estimation of system parameters of linear dynamical systems with bounded disturbances, which is motivated by robust (adaptive) constrained control. Departing from the confidence bounds of least square estimation from the machine-learning literature, this paper focuses on a method commonly used in (robust constrained) control literature: set membership estimation (SME). SME tends to enjoy better empirical performance than LSE's confidence bounds when the system disturbances are bounded. However, the theoretical guarantees of SME are not fully addressed even for i.i.d. bounded disturbances. In the literature, SME's convergence has been proved for general convex supports of the disturbances, but SME's convergence rate assumes a special type of disturbance support: $l_\infty$ ball. The main contribution of this paper is relaxing the assumption on the disturbance support and establishing the convergence rates of SME for general convex supports, which closes the gap on the applicability of the convergence and convergence rates results. Numerical experiments on SME and LSE's confidence bounds are also provided for different disturbance supports.
View PDF Chat

CEPC Technical Design Report: Accelerator

2024-03-01
Waleed Abdallah , K. Afanaciev , Shakeel Ahmad +7 more
View PDF Chat

Non-asymptotic System Identification for Linear Systems with Nonlinear Policies

2023-01-01
Yingying Li , Tianpeng Zhang , Subhro Das +2 more
This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control … This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control for constrained linear systems, where the safe policies during the learning process are usually nonlinear and time-varying for satisfying the state and input constraints. In this paper, we provide a non-asymptotic error bound for least square estimation when the data trajectory is generated by any nonlinear and/or time-varying policies as long as the generated state and action trajectories are bounded. This significantly generalizes the existing non-asymptotic guarantees for linear system identification, which usually consider i.i.d. random inputs or linear policies. Interestingly, our error bound is consistent with that for linear policies with respect to the dependence on the trajectory length, system dimensions, and excitation levels. Lastly, we demonstrate the applications of our results by safe learning with robust model predictive control and provide numerical analysis.
View PDF Chat

Observation of whistler wave instability driven by temperature anisotropy of energetic electrons on EXL-50 spherical torus

2023-01-01
Mingyuan Wang , Yuejiang Shi , Jiaqi Dong +7 more
Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to … Electromagnetic modes in the frequency range of 30-120MHz were observed in electron cyclotron wave (ECW) steady state plasmas on the ENN XuanLong-50 (EXL-50) spherical torus. These modes were found to have multiple bands of frequencies proportional to the Alfv\'en velocity. This indicates that the observed mode frequencies satisfy the dispersion relation of whistler waves. In addition, suppression of the whistler waves by the synergistic effect of Lower Hybrid Wave (LHW) and ECW was also observed. This suggests that the whistler waves were driven by temperature anisotropy of energetic electrons. These are the first such observations (not runaway discharge) made in magnetically confined toroidal plasmas and may have important implications for studying wave-particle interactions, RF wave current driver, and runaway electron control in future fusion devices.

Learning the Uncertainty Sets for Control Dynamics via Set Membership: A Non-Asymptotic Analysis

2023-01-01
Yingying Li , Jing Yu , Lauren Conger +1 more
Set-membership estimation is commonly used in adaptive/learning-based control algorithms that require robustness over the model uncertainty sets, e.g., online robustly stabilizing control and robust adaptive model predictive control. Despite having … Set-membership estimation is commonly used in adaptive/learning-based control algorithms that require robustness over the model uncertainty sets, e.g., online robustly stabilizing control and robust adaptive model predictive control. Despite having broad applications, non-asymptotic estimation error bounds in the stochastic setting are limited. This paper provides such a non-asymptotic bound on the diameter of the uncertainty sets generated by set membership estimation on linear dynamical systems under bounded, i.i.d. disturbances. Further, this result is applied to robust adaptive model predictive control with uncertainty sets updated by set membership. We numerically demonstrate the performance of the robust adaptive controller, which rapidly approaches the performance of the offline optimal model predictive controller, in comparison with the control design based on least square estimation's confidence regions.
View PDF Chat

Non-asymptotic System Identification for Linear Systems with Nonlinear Policies

2023-01-01
Yingying Li , Tianpeng Zhang , Subhro Das +2 more
This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control … This paper considers a single-trajectory system identification problem for linear systems under general nonlinear and/or time-varying policies with i.i.d. random excitation noises. The problem is motivated by safe learning-based control for constrained linear systems, where the safe policies during the learning process are usually nonlinear and time-varying for satisfying the state and input constraints. In this paper, we provide a non-asymptotic error bound for least square estimation when the data trajectory is generated by any nonlinear and/or time-varying policies as long as the generated state and action trajectories are bounded. This significantly generalizes the existing non-asymptotic guarantees for linear system identification, which usually consider i.i.d. random inputs or linear policies. Interestingly, our error bound is consistent with that for linear policies with respect to the dependence on the trajectory length, system dimensions, and excitation levels. Lastly, we demonstrate the applications of our results by safe learning with robust model predictive control and provide numerical analysis.
View PDF Chat

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

2022-05-20
Yuejiang Shi , Bing Liu , Shaodong Song +7 more
Abstract As a new spherical tokamak designed to simplify the engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio vacuum vessel (VV), … Abstract As a new spherical tokamak designed to simplify the engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard x-ray detectors, carry the bulk of the plasma current ranging from 50–150 kA, which is maintained for more than 1 s duration. It is observed that over one ampere current can be sustained per watt of ECRH power issued from the 28 GHz gyrotrons. The plasma current reaches I p &gt; 80 kA for high density (&gt;5 × 10 18 m −2 ) discharge with 150 kW ECRH. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates a smaller closed magnetic-flux surface of low aspect ratio that in turn confines the thermal plasma electrons and ions and participate in maintaining the equilibrium force balance.
View PDF Chat

Experimental study of the characteristics of energetic electrons outside LCFS in EXL-50 spherical torus

2022-03-02
Dong Guo , Yuejiang Shi , Wenjun Liu +7 more
Abstract Significant number of confined energetic electrons have been observed outside of the LCFS (last-closed flux surface) of EXL-50’s solenoid-free electron cyclotron resonance heating (ECRH) sustained plasmas. Several measurement technologies … Abstract Significant number of confined energetic electrons have been observed outside of the LCFS (last-closed flux surface) of EXL-50’s solenoid-free electron cyclotron resonance heating (ECRH) sustained plasmas. Several measurement technologies have been applied to verify the key characteristics of energetic electrons for the first time. Experiments reveal that the presence of high-temperature, low-density electrons can carry relatively large quantities of the stored energy. The boundary between the thermal plasma and the energetic fluid is clearly separated and the distance between the two boundaries can reach tens of centimeters (around the size of the minor radius of the thermal plasma). This implies that the Grad-Shafranov equilibrium is not adequate to describe the equilibrium of EXL-50 plasma and a multi-fluid model is required. Particle simulations of full orbits show that energetic electrons can be well confined outside the LCFS. This is consistent with the experimental observations.
View PDF Chat

A Wasserstein distance-based spectral clustering method for transaction data analysis

2022-01-01
Yingqiu Zhu , Danyang Huang , Yingying Li +1 more
With the rapid development of online payment platforms, it is now possible to record massive transaction data. Clustering on transaction data significantly contributes to analyzing merchants' behavior patterns. This enables … With the rapid development of online payment platforms, it is now possible to record massive transaction data. Clustering on transaction data significantly contributes to analyzing merchants' behavior patterns. This enables payment platforms to provide differentiated services or implement risk management strategies. However, traditional methods exploit transactions by generating low-dimensional features, leading to inevitable information loss. In this study, we use the empirical cumulative distribution of transactions to characterize merchants. We adopt Wasserstein distance to measure the dissimilarity between any two merchants and propose the Wasserstein-distance-based spectral clustering (WSC) approach. Based on the similarities between merchants' transaction distributions, a graph of merchants is generated. Thus, we treat the clustering of merchants as a graph-cut problem and solve it under the framework of spectral clustering. To ensure feasibility of the proposed method on large-scale datasets with limited computational resources, we propose a subsampling method for WSC (SubWSC). The associated theoretical properties are investigated to verify the efficiency of the proposed approach. The simulations and empirical study demonstrate that the proposed method outperforms feature-based methods in finding behavior patterns of merchants.
View PDF Chat

First Identification of New X-Ray Spectra of Mo39+, Mo40+, W43+, W44+ and W45+ on EAST

2022-01-01
Fudi Wang , Dian Lu , Mingfeng Gu +7 more
New high-resolution x-ray spectra of Mo39+, Mo40+, W43+, W44+ and W45+ have been carefully confirmed for the first time by use of the x-ray imaging crystal spectrometer (XCS) in Experimental … New high-resolution x-ray spectra of Mo39+, Mo40+, W43+, W44+ and W45+ have been carefully confirmed for the first time by use of the x-ray imaging crystal spectrometer (XCS) in Experimental Advanced Superconducting Tokamak (EAST) under various combined auxiliary heating plasmas conditions. Wavelength of these new x-ray spectra is ranged from 3.895 {\AA} to 3.986 {\AA}. When core electron temperature (Te0) reaches 6.0 keV, Mo39+ and Mo40+ lines of 3.9727, 3.9294 and 3.9480 {\AA} can be effectively detected on XCS for EAST; meanwhile, line-integrated brightness of these spectral lines of Mo39+ and Mo40+ is very considerable when electron temperature reaches 12.9 keV. Multi-components spectral lines for W43+, W44+ and W45+ have also been identified when Te0 reaches 6 keV. Parts of spectral lines, such as Zn-1, Cu-2, Cu-4a, Cu-4d and Cu-5 lines of tungsten, are first observed experimentally. When electron temperature reaches 12.9 keV, line-integrated intensity for part of these spectral lines of W43+, W44+ and W45+ are considerable. These experimental results and theoretical predictions from FAC and FLYCHK codes are in good general agreement. These new spectral lines, obtained on XCS for EAST, are vital for deeply uncovering the mechanisms of ion and electron thermal, high-Z impurity and momentum (anomalous) transport to achieve the advanced steady-state operation scenarios for ITER and CFETR.

Advancement of Photospheric Radius Expansion and Clocked Type-I X-Ray Burst Models with the New <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Mg</mml:mi></mml:mrow><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>22</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mi>α</mml:mi><mml:mo>,</mml:mo><mml:mi>p</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:mmultiscripts><mml:…

2021-10-19
Jun Hu , H. Yamaguchi , Y. H. Lam +7 more
We report the first (in)elastic scattering measurement of ^{25}Al+p with the capability to select and measure in a broad energy range the proton resonances in ^{26}Si contributing to the ^{22}Mg(α,p) … We report the first (in)elastic scattering measurement of ^{25}Al+p with the capability to select and measure in a broad energy range the proton resonances in ^{26}Si contributing to the ^{22}Mg(α,p) reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the α threshold of ^{26}Si that are found to strongly impact the ^{22}Mg(α,p) rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS 1826-24 clocked burster with mean deviation <9% and permits us to discover a strong correlation between the He abundance in the accreting envelope of the photospheric radius expansion burster and the dominance of ^{22}Mg(α,p) branch.
View PDF Chat

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

2021-05-10
Yuejiang Shi , Bing Liu , Shaodong Song +7 more
Abstract As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel … Abstract As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to possibly improve current drive effectiveness. The energetic electrons are observed via hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current with high line-density (approaching 1019m-2) has been achieved for plasma currents as high as 76kA. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.
View PDF Chat

Observation of a strong correlation between the positive floating potential near the edge and plasma current on EXL-50 ECW plasma

2021-01-01
Mingyuan Wang , Dong Guo , Xin Zhao +7 more
Fully non-inductive plasma current start-up without the central solenoid in ECW plasma was used on EXL-50 Spherical Torus with a weak external vertical field (Bv). Generally, the number of electrons … Fully non-inductive plasma current start-up without the central solenoid in ECW plasma was used on EXL-50 Spherical Torus with a weak external vertical field (Bv). Generally, the number of electrons leaving to the vessel wall by the gradient Bt is larger than ions, and the positive potential was built up in plasma. The relationship between floating potential and the plasma current was studied using the Langmuir probes near the boundary. The results show that the floating potential is positive (about 200V) and has a strong correlation with plasma current. In open magnetic field, the plasma current is driven by the high energy electrons in preferential confinement, the plasma current and potential approximately positively correlated with total electron density. After forming the closed flux surface, the plasma current consists mainly of the ECW driven current, and potential is negatively correlated with plasma current. By actively adjusting the Bv, it demonstrated that the positive voltage is approximately inversely correlated with the Bv and plasma current (Ip). Considering that the plasma temperature near the boundary is quite low (~eV), the positive voltage near the boundary caused by the high-energy electron loss. Therefore, the measurements of the boundary potential are important for the study of high-energy electron confinement performance, noninductive plasma current start-up and current driven.
View PDF Chat

Non-inductive plasma current sustainment with stochastic electron cyclotron in EXL-50 spherical torus

2021-01-01
Mingyuan Wang , Shikui Cheng , Bing Liu +7 more
The start-up and sustainment of a stochastic wave non-inductive current on a spherical torus was experimentally demonstrated for the first time using only electron cyclotron waves. The plasma current is … The start-up and sustainment of a stochastic wave non-inductive current on a spherical torus was experimentally demonstrated for the first time using only electron cyclotron waves. The plasma current is insensitive to the injection angle of ECWs and approximately linearly correlated with the slope of the X-ray spectrum. Its direction is determined by the vertical magnetic field (BV). The temporal development in the number of X-ray bremsstrahlung photons with a specified energy is consistent with the stochastic heating model. Moreover, the ratio of Amps to Watts of the ECW is generally &gt;1 kA/kW under normal conditions (maximum plasma current: 150 kA, ECW: 140 kW). The experimental results are explained using the stochastic heating model of the asymmetric electron velocity distribution in stochastic electromagnetic waves.

Safe Adaptive Learning-based Control for Constrained Linear Quadratic Regulators with Regret Guarantees

2021-01-01
Yingying Li , Subhro Das , Jeff S. Shamma +1 more
We study the adaptive control of an unknown linear system with a quadratic cost function subject to safety constraints on both the states and actions. The challenges of this problem … We study the adaptive control of an unknown linear system with a quadratic cost function subject to safety constraints on both the states and actions. The challenges of this problem arise from the tension among safety, exploration, performance, and computation. To address these challenges, we propose a polynomial-time algorithm that guarantees feasibility and constraint satisfaction with high probability under proper conditions. Our algorithm is implemented on a single trajectory and does not require system restarts. Further, we analyze the regret of our learning algorithm compared to the optimal safe linear controller with known model information. The proposed algorithm can achieve a $\tilde O(T^{2/3})$ regret, where $T$ is the number of stages and $\tilde O(\cdot)$ absorbs some logarithmic terms of $T$.
View PDF Chat

Probing the local electronic structure of isovalent Bi atoms in InP

2020-01-31
C. M. Krammel , Adonai Rodrigues da Cruz , Michael E. Flatté +7 more
Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. We map the spatial pattern of the Bi … Cross-sectional scanning tunneling microscopy (X-STM) is used to experimentally study the influence of isovalent Bi atoms on the electronic structure of InP. We map the spatial pattern of the Bi impurity state, which originates from Bi atoms down to the sixth layer below the surface, in topographic, filled-state X-STM images on the natural ${110}$ cleavage planes. The Bi impurity state has a highly anisotropic bowtielike structure and extends over several lattice sites. These Bi-induced charge redistributions extend along the $\ensuremath{\langle}110\ensuremath{\rangle}$ directions, which define the bowtielike structures we observe. Local tight-binding calculations reproduce the experimentally observed spatial structure of the Bi impurity state. In addition, the influence of the Bi atoms on the electronic structure is investigated in scanning tunneling spectroscopy measurements. These measurements show that Bi induces a resonant state in the valence band, which shifts the band edge toward higher energies. Furthermore, we show that the energetic position of the Bi-induced resonance and its influence on the onset of the valence band edge depend crucially on the position of the Bi atoms relative to the cleavage plane.
View PDF Chat

I-mode investigation on the Experimental Advanced Superconducting Tokamak

2019-06-11
Xi Feng , A. D. Liu , C. Zhou +7 more
By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak.During the L-mode to I-mode transition, the energy … By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak.During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode.Similar with the I-mode observation on other devices, the E r profiles obtained by the eight-channel Doppler backscattering system (DBS8) [1] show a deeper edge E r well in the I-mode than that in the L-mode.And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm.WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the E r fluctuation and the caused flow shear from WCM should play an important role during I-mode.In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared.Many evidences show that the a low-frequency oscillation may be a
View PDF Chat

Low Mach number limit of strong solutions for 3-D full compressible MHD equations with Dirichlet boundary condition

2019-01-01
Lan Zeng , Guoxi Ni , Yingying Li
In this paper, we consider the low Mach number limit of the full compressible MHD equations in a 3-D bounded domain with Dirichlet boundary condition for velocity field, Neumann boundary … In this paper, we consider the low Mach number limit of the full compressible MHD equations in a 3-D bounded domain with Dirichlet boundary condition for velocity field, Neumann boundary condition for temperature and perfectly conducting boundary condition for magnetic field. First, the uniform estimates in the Mach number for the strong solutions are obtained in a short time interval, provided that the initial density and temperature are close to the constant states. Then, we prove the solutions of the full compressible MHD equations converge to the isentropic incompressible MHD equations as the Mach number tends to zero.

Distributed Reinforcement Learning for Decentralized Linear Quadratic Control: A Derivative-Free Policy Optimization Approach

2019-01-01
Yingying Li , Yujie Tang , Runyu Zhang +1 more
This paper considers a distributed reinforcement learning problem for decentralized linear quadratic control with partial state observations and local costs. We propose a Zero-Order Distributed Policy Optimization algorithm (ZODPO) that … This paper considers a distributed reinforcement learning problem for decentralized linear quadratic control with partial state observations and local costs. We propose a Zero-Order Distributed Policy Optimization algorithm (ZODPO) that learns linear local controllers in a distributed fashion, leveraging the ideas of policy gradient, zero-order optimization and consensus algorithms. In ZODPO, each agent estimates the global cost by consensus, and then conducts local policy gradient in parallel based on zero-order gradient estimation. ZODPO only requires limited communication and storage even in large-scale systems. Further, we investigate the nonasymptotic performance of ZODPO and show that the sample complexity to approach a stationary point is polynomial with the error tolerance's inverse and the problem dimensions, demonstrating the scalability of ZODPO. We also show that the controllers generated throughout ZODPO are stabilizing controllers with high probability. Lastly, we numerically test ZODPO on multi-zone HVAC systems.
View PDF Chat

CEPC Conceptual Design Report: Volume 2 - Physics &amp; Detector

2018-01-01
J. Barreiro Guimarães da Costa , J. Qian , C. Tully +7 more
The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the … The Circular Electron Positron Collider (CEPC) is a large international scientific facility proposed by the Chinese particle physics community to explore the Higgs boson and provide critical tests of the underlying fundamental physics principles of the Standard Model that might reveal new physics. The CEPC, to be hosted in China in a circular underground tunnel of approximately 100 km in circumference, is designed to operate as a Higgs factory producing electron-positron collisions with a center-of-mass energy of 240 GeV. The collider will also operate at around 91.2 GeV, as a Z factory, and at the WW production threshold (around 160 GeV). The CEPC will produce close to one trillion Z bosons, 100 million W bosons and over one million Higgs bosons. The vast amount of bottom quarks, charm quarks and tau-leptons produced in the decays of the Z bosons also makes the CEPC an effective B-factory and tau-charm factory. The CEPC will have two interaction points where two large detectors will be located. This document is the second volume of the CEPC Conceptual Design Report (CDR). It presents the physics case for the CEPC, describes conceptual designs of possible detectors and their technological options, highlights the expected detector and physics performance, and discusses future plans for detector R&amp;D and physics investigations. The final CEPC detectors will be proposed and built by international collaborations but they are likely to be composed of the detector technologies included in the conceptual designs described in this document. A separate volume, Volume I, recently released, describes the design of the CEPC accelerator complex, its associated civil engineering, and strategic alternative scenarios.
View PDF Chat

On the estimation of integrated covariance matrices of high dimensional diffusion processes

2012-03-01
Xinghua Zheng , Yingying Li
We consider the estimation of integrated covariance (ICV) matrices of high dimensional diffusion processes based on high frequency observations. We start by studying the most commonly used estimator, the realized … We consider the estimation of integrated covariance (ICV) matrices of high dimensional diffusion processes based on high frequency observations. We start by studying the most commonly used estimator, the realized covariance (RCV) matrix. We show that in the high dimensional case when the dimension $p$ and the observation frequency $n$ grow in the same rate, the limiting spectral distribution (LSD) of RCV depends on the covolatility process not only through the targeting ICV, but also on how the covolatility process varies in time. We establish a Mar\v{c}enko--Pastur type theorem for weighted sample covariance matrices, based on which we obtain a Mar\v{c}enko--Pastur type theorem for RCV for a class $\mathcal{C}$ of diffusion processes. The results explicitly demonstrate how the time variability of the covolatility process affects the LSD of RCV. We further propose an alternative estimator, the time-variation adjusted realized covariance (TVARCV) matrix. We show that for processes in class $\mathcal {C}$, the TVARCV possesses the desirable property that its LSD depends solely on that of the targeting ICV through the Mar\v{c}enko--Pastur equation, and hence, in particular, the TVARCV can be used to recover the empirical spectral distribution of the ICV by using existing algorithms.

Unconventional superconducting phase in the weakly correlated noncentrosymmetric<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>Mo</mml:mtext></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>Al</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mtext>C</mml:mtext></mml:mrow></mml:math>compound

2010-08-17
E. Bauer , Gerda Rogl , Xing‐Qiu Chen +7 more
Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ ($\ensuremath{\beta}\text{-Mn}$ type, space group $P{4}_{1}32$) as a strong-coupled superconductor with ${T}_{c}=9\text{ }\text{K}$ deviating notably from BCS-type behavior. The absence of a … Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ ($\ensuremath{\beta}\text{-Mn}$ type, space group $P{4}_{1}32$) as a strong-coupled superconductor with ${T}_{c}=9\text{ }\text{K}$ deviating notably from BCS-type behavior. The absence of a Hebbel-Slichter peak, a power-law behavior of the spin-lattice relaxation rate (from $^{27}\text{A}\text{l}$ NMR), an electronic specific heat strongly deviating from BCS model and a pressure enhanced ${T}_{c}$ suggest unconventional superconductivity with possibly a nodal structure of the superconducting gap. Relativistic density-functional theory calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favoring a mix of spin-singlet and spin-triplet components in the superconducting condensate, in absence of strong correlations among electrons.
View PDF Chat
Coauthor Papers Together
Yuejiang Shi 7
Y.K.M. Peng 5
Songjian Li 5
Mingyuan Wang 5
Bing Liu 5
Na Li 4
Dong Guo 4
Shaodong Song 4
Shikui Cheng 4
D. Banerjee 4
Minsheng Liu 3
Wenjun Liu 3
Yunyang Song 3
Subhro Das 3
Baoshan Yuan 3
Xin Zhao 3
Xiao-Gang He 3
Tiantian Sun 3
Tiantian Sun 3
Jeff S. Shamma 3
Fu-Sheng Yu 3
Xianming Song 3
Shan Cheng 2
V. Boudry 2
Xinpeng Ma 2
Emilie Passemar 2
Manqi Ruan 2
Ze Yin 2
Guang-You Qin 2
Abdesslam Arhrib 2
Juan José Sanz-Cillero 2
Linhao Zhang 2
Kai Ma 2
Xiaohao Cui 2
B. Di Micco 2
Wei-Tian Deng 2
Bin Yan 2
Lingling Men 2
Michael Sullivan 2
Yuanjie Bi 2
Rocco Paparella 2
Zhongjian Ma 2
Tianya Wu 2
Miaohui Li 2
Jianshe Cao 2
Ruilin Zhu 2
Akio Ishida 2
Zhenchao Liu 2
Shufang Su 2
Xiang Liu 2