arXiv subjects

Rong Liu

Publications and source records attributed to Rong Liu.

At least 55 records · Page 3Linked to original sources

arXiv2020

Measurement of the neutron beam profile of the Back-n white neutron facility at CSNS with a Micromegas detector

The Back-n white neutron beam line, which uses back-streaming white neutrons from the spallation target of the China Spallation Neutron Source, is used for nuclear data measurements. A Micromegas-based neutron detector with two variants was specially developed to measure the beam spot distribution for this beam line. In this article, the design, fabrication, and characterization of the detector are described. The results of the detector performance tests are presented, which include the relative electron transparency, the gain and the gain uniformity, and the neutron beam profile reconstruction capability. The result of the first measurement of the Back-n neutron beam spot distribution is also presented.

physics.ins-det↗

arXiv2019

Measurements of differential and angle-integrated cross sections for the $^{10}$B($n, α$)$^{7}$Li reaction in the neutron energy range from 1.0 eV to 2.5 MeV

Differential and angle-integrated cross sections for the $^{10}$B($n, α$)$^{7}$Li, $^{10}$B($n, α$$_{0}$)$^{7}$Li and $^{10}$B($n, α$$_{1}$)$^{7}$Li$^{*}$ reactions have been measured at CSNS Back-n white neutron source. Two enriched (90%) $^{10}$B samples 5.0 cm in diameter and ~85.0 $μ$g/cm$^{2}$ in thickness each with an aluminum backing were prepared, and back-to-back mounted at the sample holder. The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array (LPDA) system. The neutron energy E$_{n}$ was determined by TOF (time-of-flight) method, and the valid $α$ events were extracted from the E$_{n}$-Amplitude two-dimensional spectrum. With 15 silicon detectors, the differential cross sections of $α$-particles were measured from 19.2° to 160.8°. Fitted with the Legendre polynomial series, the ($n, α$) cross sections were obtained through integration. The absolute cross sections were normalized using the standard cross sections of the $^{10}$B($n, α$)$^{7}$Li reaction in the 0.3 - 0.5 MeV neutron energy region. The measurement neutron energy range for the $^{10}$B($n, α$)$^{7}$Li reaction is 1.0 eV $\le$ En < 2.5 MeV (67 energy points), and for the $^{10}$B($n, α$$_{0}$)$^{7}$Li and $^{10}$B($n, α$$_{1}$)$^{7}$Li$^{*}$ reactions is 1.0 eV $\le$ En < 1.0 MeV (59 energy points). The present results have been analyzed by the resonance reaction mechanism and the level structure of the $^{11}$B compound system, and compared with existing measurements and evaluations.

nucl-ex↗

arXiv2019

Alternative Analysis Methods for Time to Event Endpoints under Non-proportional Hazards: A Comparative Analysis

The log-rank test is most powerful under proportional hazards (PH). In practice, non-PH patterns are often observed in clinical trials, such as in immuno-oncology; therefore, alternative methods are needed to restore the efficiency of statistical testing. Three categories of testing methods were evaluated, including weighted log-rank tests, Kaplan-Meier curve-based tests (including weighted Kaplan-Meier and Restricted Mean Survival Time, RMST), and combination tests (including Breslow test, Lee's combo test, and MaxCombo test). Nine scenarios representing the PH and various non-PH patterns were simulated. The power, type I error, and effect estimates of each method were compared. In general, all tests control type I error well. There is not a single most powerful test across all scenarios. In the absence of prior knowledge regarding the PH or non-PH patterns, the MaxCombo test is relatively robust across patterns. Since the treatment effect changes overtime under non-PH, the overall profile of the treatment effect may not be represented comprehensively based on a single measure. Thus, multiple measures of the treatment effect should be pre-specified as sensitivity analyses to evaluate the totality of the data.

stat.AP↗

arXiv2019

Amplitude-modulated pulses based phase-sensitive OTDR in distributed sensing

The detected frequency response range of phase-sensitive optical time domain reflectometry is limited by the sensing fiber length. In this paper, we demonstrate an amplitude modulated pulses based phase-sensitive OTDR to detect vibrations with high spatial resolution and wide frequency response range. The amplitude modulated pulses consisting of narrow pulses and background light are injected into the sensing fiber as probe light. The Rayleigh backscattering generated by the background light interferes at the detection end, presenting a phase sensitive response to external vibrations. The Rayleigh backscattering of narrow pulses are tracked to locate vibrations. The frequency information is obtained from the frequency domain analysis of the interference signal. The system can realize high frequency response with low repetition rate of probe pulses by one-end detection.

physics.app-ph↗

arXiv2019

The detection of non-Gaussian vibrations with improved spatial resolution and signal-to-noise ratio in distributed sensing

In fiber-optic distributed sensing, vibration signals are mostly assumed to follow Gaussian distribution for the simplicity of signal processing. However, in real applications, vibration signals often behave as non-Gaussian processes, which have rarely been highly considered. In this paper, a higher-order cumulants algorithm based phase-sensitive optical time-domain reflectometry (OTDR) is proposed to detect and analyze non-Gaussian vibration signals accompanied with noises. When disturbances are applied on the sensing fiber, the distribution probability of Rayleigh backscattering signals will deviate from the ideal Gaussian distribution. The non-Gaussian vibration is then extracted from Gaussian noises based on the probability density distribution. Simulations and experiments are carried out. The experimental results show that the demonstrated method can measure non-Gaussian vibrations with improved signal-to-noise ratio and spatial resolution.

eess.SP↗

arXiv2018

Intertrochanteric Fracture Visualization and Analysis Using a Map Projection Technique

Understanding intertrochanteric fracture distribution is an important topic in orthopaedics due to its high morbidity and mortality. The intertrochanteric fracture can contain high-dimensional information including complicated 3D fracture lines, which often make it difficult to visualize or to obtain valuable statistics for clinical diagnosis and prognosis applications. This paper proposed a map projection technique to map the high-dimensional information into a 2D parametric space. This method can preserve the 3D proximal femur surface and structure while visualizing the entire fracture line with a single plot/view. Using this method and a standardization technique, a total of 100 patients with different ages and genders are studied based on the original radiographs acquired by CT scan. The comparison shows that the proposed map projection representation is more efficient and rich in information visualization than the conventional heat map technique. Using the proposed method, a fracture probability can be obtained at any location in the 2D parametric space, from which the most probable fracture region can be accurately identified. The study shows that age and gender have significant influences on intertrochanteric fracture frequency and fracture line distribution.

q-bio.QM↗

arXiv2017

Hardy Spaces over Half-strip Domains

We define Hardy spaces $H^p(Ω_\pm)$ on half-strip domain~$Ω_+$ and $Ω_-= \mathbb{C}\setminus\overline{Ω_+}$, where $0<p<\infty$, and prove that functions in $H^p(Ω_\pm)$ has non-tangential boundary limit a.e. on $Γ$, the common boundary of $Ω_\pm$. We then prove that Cauchy integral of functions in $L^p(Γ)$ are in $H^p(Ω_\pm)$, where $1<p<\infty$, that is, Cauchy transform is bounded. Besides, if $1\leqslant p<\infty$, then $H^p(Ω_\pm)$ functions are the Cauchy integral of their non-tangential boundary limits. We also establish an isomorphism between $H^p(Ω_\pm)$ and $H^p(\mathbb{C}_\pm)$, the classical Hardy spaces over upper and lower half complex planes.

math.CV↗

arXiv2017

Notes of Boundedness on Cauchy Integrals on Lipschitz Curves ($p=2$)

We provide the details of the first proof in~\cite{CJS89}, which proved that Cauchy transform of $L^2$~functions on Lipschitz curves is bounded. We then prove that every $L^2$~function on Lipschitz curves is the sum of non-tangential boundary limit of functions in $H^2(Ω_\pm)$, the Hardy spaces on domains over and under the Lipschitz curve. We also obtain a more accurate boundary of Cauchy transform under the condition that the Lipschitz curve is the real axis.

math.CV↗

arXiv2017

Hardy Spaces ($1<p<\infty$) over Lipschitz Domains

Let $Γ$ be a Lipschitz curve on the complex plane $\mathbb{C}$ and $Ω_+$ is the domain above $Γ$, we define Hardy space $H^p(Ω_+)$ as the set of holomorphic functions $F$ satisfying $\sup_{τ>0}(\int_Γ |F(ζ+\mathrm{i}τ)|^p |\,\mathrm{d}ζ|)^{\frac1p}< \infty$. We mainly focus on the case of $1<p<\infty$ in this paper, and prove that if $F(w)\in H^p(Ω_+)$, then $F(w)$ has non-tangential boundary limit $F(ζ)$ a.e. on $Γ$, and $F(w)$ is the Cauchy integral of $F(ζ)$. We denote the conformal mapping from $\mathbb{C}_+$ onto $Ω_+$ as $Φ$, and then prove that, $ H^p(Ω_+)$ is isomorphic to $H^p(\mathbb{C}_+)$, the classical Hardy space on upper half plane, under the mapping $T\colon F\to F(Φ(z))\cdot (Φ'(z))^\frac{1}{p}$, where $F\in H^p(Ω_+)$.

math.CV↗

arXiv2017

Hardy Spaces ($0<p<\infty$) over Lipschitz Domains

Let $0 0}(\int_Γ |F(ζ+\mathrm{i}τ)|^p |\,\mathrm{d}ζ|)^{\frac1p}< \infty$. We denote the conformal mapping from $\mathbb{C}_+$ onto $Ω_+$ as $Φ$, and prove that, $H^p(Ω_+)$ is isomorphic to $H^p(\mathbb{C}_+)$, the classical Hardy space on the upper half plane~$\mathbb{C}_+$, under the mapping $T\colon F\to F(Φ)\cdot (Φ')^{\frac1p}$. Besides, $T$ and $T^{-1}$ are both bounded. We also prove that if $F(w)\in H^p(Ω_+)$, then $F(w)$ has non-tangential boundary limit $F(ζ)$ a.e. on $Γ$, and, if $1\leqslant p< \infty$, $F(w)$ is the Cauchy integral on $Γ$ of $F(ζ)$.

math.CV↗

arXiv2017

Commissioning of te China-ADS injector-I testing facility

The 10 MeV accelerator-driven subcritical system (ADS) Injector-I test stand at Institute of High Energy Physics (IHEP) is a testing facility dedicated to demonstrate one of the two injector design schemes [Injector Scheme-I, which works at 325 MHz], for the ADS project in China. The Injector adopted a four vane copper structure RFQ with output energy of 3.2 MeV and a superconducting (SC) section accommodating fourteen \b{eta}g=0.12 single spoke cavities, fourteen SC solenoids and fourteen cold BPMs. The ion source was installed since April of 2014, periods of commissioning are regularly scheduled between installation phases of the rest of the injector. Continuous wave (CW) beam was shooting through the injector and 10 MeV CW proton beam with average beam current around 2 mA was obtained recently. This contribution describe the results achieved so far and the difficulties encountered in CW commissioning.

physics.acc-ph↗

arXiv2016

Measurement of the transfer function for a spoke cavity of C-ADS Injector I

The spoke cavities mounted in the China Accelerator Driven sub-critical System (C-ADS) have high quality factor(Q) and very small bandwidth, making them very sensitive to mechanical perturbations whether external or self-induced. The transfer function is used to characterize the response of the cavity eigen frequency to the perturbations. This paper describes a method to measure the transfer function of a spoke cavity. The measured Lorentz transfer function shows there are 206 Hz and 311 Hz mechanical eigenmodes excited by Lorentz force in the cavity of C-ADS, and the measured piezo fast tuner transfer function shows there are 12 mechanical eigenmodes from 0 to 500 Hz. According to these results, some effective measures have been taken to weaken the influence from helium pressure fluctuation, avoid mechanical resonances and improve the reliability of RF system.

physics.acc-ph↗

arXiv2016

Implement and commissioning of the beam energy feedback system in BEPCII linac

In order to ensure the beam quality and meet the requirements introduced by the BEPCII storage ring, the beam energy feedback system has been developed at the exit of the linac. This paper describes the implementation and commissioning of this system in detail. The energy feedback system consists of an energy measurement unit, an application software and an execution unit. In order to ensure the real-time monitoring and adjustment of beam energy, we need to introduce a non-interceptive type of online beam energy measurement method which is on the first try in China and the effective mechanism of energy adjustment to achieve this goal. The adjustment of energy is achieved by adjusting the output microwave phase of the RF power source station. The system was put into operation in March 16th, 2016 and achieved the desired results. It can effectively eliminate the low point of the injection rate caused by the fluctuation of the beam center energy and has played an important role in maintaining a high constant injection rate.

physics.acc-ph↗

arXiv2016

Tuner control system of spoke012 SRF cavity for C-ADS injector I at IHEP

A new tuner control system of spoke superconducting radio frequency (SRF) cavity has been developed and applied to cryomodule I (CM1) of C-ADS injector I at IHEP. We have successfully implemented the tuner controllerfor the first time and achieved a cavity tuning phase error of 0.7degrees (about 4 Hz peak to peak) in the presence of electromechanical coupled resonance. This paper will present the preliminary experimental results based on the new tuner controller under proton beam commissioning.

physics.acc-ph↗

arXiv2015

Stochastic Top-k ListNet

ListNet is a well-known listwise learning to rank model and has gained much attention in recent years. A particular problem of ListNet, however, is the high computation complexity in model training, mainly due to the large number of object permutations involved in computing the gradients. This paper proposes a stochastic ListNet approach which computes the gradient within a bounded permutation subset. It significantly reduces the computation complexity of model training and allows extension to Top-k models, which is impossible with the conventional implementation based on full-set permutations. Meanwhile, the new approach utilizes partial ranking information of human labels, which helps improve model quality. Our experiments demonstrated that the stochastic ListNet method indeed leads to better ranking performance and speeds up the model training remarkably.

cs.IR↗

arXiv2015

Beam energy online measurement of BEPCII LINAC

This paper describes beam energy online measurement of BEPCII linac, presents the calculation formula and some of the results. The method mentioned here measures the beam energy by acquiring beam positions in the horizontal direction with three beam position monitors (BPM) eliminating the effect of orbit fluctuation, which is much better than the one using the single BPM. The error analysis indicates that this online measurement has further potential usage such as a part of beam energy feedback system. The reliability of this method is also discussed and demonstrated in the end of this paper.

physics.acc-ph↗

arXiv2015

Learning from LDA using Deep Neural Networks

Latent Dirichlet Allocation (LDA) is a three-level hierarchical Bayesian model for topic inference. In spite of its great success, inferring the latent topic distribution with LDA is time-consuming. Motivated by the transfer learning approach proposed by~\newcite{hinton2015distilling}, we present a novel method that uses LDA to supervise the training of a deep neural network (DNN), so that the DNN can approximate the costly LDA inference with less computation. Our experiments on a document classification task show that a simple DNN can learn the LDA behavior pretty well, while the inference is speeded up tens or hundreds of times.

cs.LG↗

arXiv2015

Method for measuring prompt gamma-rays generated by D-T neutrons bombarding a depleted uranium spherical shell

The prompt gamma-ray spectrum from depleted uranium (DU) spherical shells induced by 14 MeV D-T neutrons is measured. Monte Carlo (MC) simulation gives the largest prompt gamma flux with the optimal thickness of the DU spherical shells 3-5 cm and the optimal frequency of neutron pulse 1 MHz. The method of time of flight and pulse shape coincidence with energy (DC-TOF) is proposed, and the subtraction of the background gamma-rays discussed in detail. The electron recoil spectrum and time spectrum of the prompt gamma-rays are obtained based on a 2"*2" BC501A liquid scintillator detector. The energy spectrum and time spectrum of prompt gamma-rays are obtained based on an iterative unfolding method that can remove the influence of γ-rays response matrix and pulsed neutron shape. The measured time spectrum and the calculated results are roughly consistent with each other. Experimental prompt gamma-ray spectrum in the 0.4-3 MeV energy region agree well with MC simulation based on the ENDF/BVI.5 library, and the discrepancies for the integral quantities of gamma-rays of energy 0.4-1 MeV and 1-3 MeV are 9.2% and 1.1%, respectively.

physics.ins-det↗