Search

Your search keyword '"Zhang, Junqiang"' showing total 723 results
Start Over Author "Zhang, Junqiang"
723 results on '"Zhang, Junqiang"'

51. Riesz Transform Characterizations of Hardy Spaces Associated to Degenerate Elliptic Operators

Author

Yang, Dachun and Zhang, Junqiang

Subjects
Mathematics - Classical Analysis and ODEs, Mathematics - Functional Analysis, Primary 47B06, Secondary 42B30, 42B35, 35J70
Abstract

Let $w$ be a Muckenhoupt $A_2(\mathbb{R}^n)$ weight and $L_w:=-w^{-1}\mathop\mathrm{div}(A\nabla)$ the degenerate elliptic operator on the Euclidean space $\mathbb{R}^n$. In this article, the authors establish the Riesz transform characterization of the Hardy space $H_{L_w}^p(\mathbb{R}^n)$ associated with $L_w$, for $w\in A_{q}(\mathbb{R}^n)$ and $w^{-1}\in A_{2-\frac{2}{n}}(\mathbb{R}^n)$ with $n\geq 3$, $q\in[1,2]$ and $p\in(q(\frac{1}{r}+\frac{q-1}{2}+\frac{1}{n})^{-1},1]$ if, for some $r\in[1,\,2)$, $\{tL_w e^{-tL_w}\}_{t\geq 0}$ satisfies the weighted $L^r-L^2$ full off-diagonal estimate., Comment: 28 pages; Submitted

Published
2015

52. Weighted $L^p$ Estimates of Kato Square Roots Associated to Degenerate Elliptic Operators

Author

Yang, Dachun and Zhang, Junqiang

Subjects
Mathematics - Classical Analysis and ODEs, Mathematics - Functional Analysis, Primary 47B06, Secondary 46E30, 35J70, 42B30, 42B35
Abstract

Let $w$ be a Muckenhoupt $A_2(\mathbb{R}^n)$ weight and $L_w:=-w^{-1}\mathop\mathrm{div}(A\nabla)$ the degenerate elliptic operator on the Euclidean space $\mathbb{R}^n$, $n\geq 2$. In this article, the authors establish some weighted $L^p$ estimates of Kato square roots associated to the degenerate elliptic operators $L_w$. More precisely, the authors prove that, for $w\in A_{p}(\mathbb{R}^n)$, $p\in(\frac{2n}{n+1},\,2]$ and any $f\in C^\infty_c(\mathbb{R}^n)$, $\|L_w^{1/2}(f)\|_{L^p(w,\,\mathbb{R}^n)}\sim \|\nabla f\|_{L^p(w,\,\mathbb{R}^n)}$, where $C_c^\infty(\mathbb{R}^n)$ denotes the set of all infinitely differential functions with compact supports., Comment: 40 pages, Submitted

Published
2015

63. Experimental demonstration of longitudinal beam phase space linearizer in a free-electron laser facility by corrugated structures

Author

Deng, Haixiao, Zhang, Meng, Feng, Chao, Zhang, Tong, Wang, Xingtao, Lan, Taihe, Feng, Lie, Zhang, Wenyan, Liu, Xiaoqing, Yao, Haifeng, Shen, Lei, Li, Bin, Zhang, Junqiang, Li, Xuan, Fang, Wencheng, Wang, Dan, Couprie, Marie-emmanuelle, Lin, Guoqiang, Liu, Bo, Gu, Qiang, Wang, Dong, and Zhao, Zhentang

Subjects
Physics - Accelerator Physics, Physics - Optics
Abstract

Removal of residual linear energy chirp and intrinsic nonlinear energy curvature in the relativistic electron beam from radiofrequency linear accelerator is of paramount importance for efficient lasing of a high-gain free-electron laser. Recently, it was theoretically and experimentally demonstrated that the longitudinal wakefield excited by the electrons itself in the corrugated structure allows for precise control of the electron beam phase space. In this Letter, we report the first utilization of a corrugated structure as beam linearizer in the operation of a seeded free-electron laser driven by a 140 MeV linear accelerator, where a gain of ~10,000 over spontaneous emission was achieved at the second harmonic of the 1047 nm seed laser, and a free-electron laser bandwidth narrowing by about 50% was observed, in good agreement with the theoretical expectations., Comment: 6 pages, 5 figures

Published
2014
Full Text
View/download PDF

69. Boundedness of Intrinsic Littlewood-Paley Functions on Musielak-Orlicz Morrey and Campanato Spaces

Author

Liang, Yiyu, Nakai, Eiichi, Yang, Dachun, and Zhang, Junqiang

Subjects
Mathematics - Classical Analysis and ODEs, Mathematics - Functional Analysis, Primary 42B25, Secondary 42B35, 46E30, 46E35
Abstract

Let $\varphi: {\mathbb R^n}\times [0,\infty)\to[0,\infty)$ be such that $\vz(x,\cdot)$ is nondecreasing, $\varphi(x,0)=0$, $\varphi(x,t)>0$ when $t>0$, $\lim_{t\to\infty}\varphi(x,t)=\infty$ and $\vz(\cdot,t)$ is a Muckenhoupt $A_\infty({\mathbb R^n})$ weight uniformly in $t$. Let $\phi: [0,\infty)\to[0,\infty)$ be nondecreasing. In this article, the authors introduce the Musielak-Orlicz Morrey space $\mathcal M^{\varphi,\phi}(\mathbb R^n)$ and obtain the boundedness on $\mathcal M^{\varphi,\phi}(\mathbb R^n)$ of the intrinsic Lusin area function $S_{\alpha}$, the intrinsic $g$-function $g_{\alpha}$, the intrinsic $g_{\lambda}^*$-function $g^\ast_{\lambda, \alpha}$ and their commutators with ${\rm BMO}(\rn)$ functions, where $\alpha\in(0,1]$, $\lambda\in(\min\{\max\{3,\,p_1\},3+2\az/n\},\infty)$ and $p_1$ denotes the uniformly upper type index of $\vz$. Let $\Phi: [0,\infty)\to[0,\infty)$ be nondecreasing, $\Phi(0)=0$, $\Phi(t)>0$ when $t>0$, and $\lim_{t\to\infty}\Phi(t)=\infty$, $w\in A_\infty(\mathbb R^n)$ and $\phi: (0,\infty)\to(0,\infty)$ be nonincreasing. The authors also introduce the weighted Orlicz-Morrey space $M_w^{\Phi,\phi}(\mathbb R^n)$ and obtain the boundedness on $M_w^{\Phi,\phi}(\mathbb R^n)$ of the aforementioned intrinsic Littlewood-Paley functions and their commutators with ${\rm BMO}(\rn)$ functions. Finally, for $q\in[1,\fz)$, the boundedness of the aforementioned intrinsic Littlewood-Paley functions on the Musielak Orlicz Campanato space $\mathcal L^{\varphi,q}(\mathbb R^n)$ is also established., Comment: 47pages, Banach J. Math. Anal. (to appear)

Published
2013

73. Efficient photocatalytic conversion of xylose to co-produce xylonic acid and CO via a dual S-scheme heterojunction photocatalyst between carbon nitride and CuInS2 quantum dot-sensitized ZnIn2S4.

Author

Liu, Kangning, Zhang, Junqiang, Ma, Jiliang, and Sun, Runcang

Subjects
*HETEROJUNCTIONS, *QUANTUM dots, *NITRIDES, *XYLOSE, *LIGHT absorption
Abstract

Heterojunction photocatalysts receive significant interest due to their high performance and easy fabrication. An S-scheme heterojunction is developed on the basis of conventional type II heterojunctions, which can further promote charge separation and migration. In this work, a photocatalyst with a dual S-scheme heterojunction (denoted as C-s-ZIS/CN) is developed by the hybridization of CuInS2 quantum dot-sensitized ZnIn2S4 nanosheets and g-C3N4 nanosheets. CuInS2 quantum dot sensitization efficiently enhanced light absorption. Meanwhile, the unique charge migration pathway in the dual S-scheme heterojunction accelerated the separation and transfer of photogenerated carriers. The photocatalyst was innovatively employed in the simultaneous photocatalytic production of xylonic acid and CO. Under 10 W LED light irradiation (790 mW cm−2), the CO evolution rate reached a high of 228.94 μmol g−1 h−1. When a xenon lamp was employed, the CO evolution rate increased to 964.27 μmol g−1 h−1. Moreover, the optimal xylonic acid yield achieved was up to 58.56%. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

74. Efficient photocatalytic conversion of xylose to co-produce xylonic acid and CO via a dual S-scheme heterojunction photocatalyst between carbon nitride and CuInS2 quantum dot-sensitized ZnIn2S4.

Author

Liu, Kangning, Zhang, Junqiang, Ma, Jiliang, and Sun, Runcang

Subjects
HETEROJUNCTIONS, QUANTUM dots, NITRIDES, XYLOSE, LIGHT absorption
Abstract

Heterojunction photocatalysts receive significant interest due to their high performance and easy fabrication. An S-scheme heterojunction is developed on the basis of conventional type II heterojunctions, which can further promote charge separation and migration. In this work, a photocatalyst with a dual S-scheme heterojunction (denoted as C-s-ZIS/CN) is developed by the hybridization of CuInS2 quantum dot-sensitized ZnIn2S4 nanosheets and g-C3N4 nanosheets. CuInS2 quantum dot sensitization efficiently enhanced light absorption. Meanwhile, the unique charge migration pathway in the dual S-scheme heterojunction accelerated the separation and transfer of photogenerated carriers. The photocatalyst was innovatively employed in the simultaneous photocatalytic production of xylonic acid and CO. Under 10 W LED light irradiation (790 mW cm−2), the CO evolution rate reached a high of 228.94 μmol g−1 h−1. When a xenon lamp was employed, the CO evolution rate increased to 964.27 μmol g−1 h−1. Moreover, the optimal xylonic acid yield achieved was up to 58.56%. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

76. Design and test of double PI-control loop to generate flat-top output of RF pulse compressor

Author

XU Yiming, ZHANG Junqiang, XIAO Chengcheng, and FANG Wencheng

Subjects
low level radio frequency, rf pulse compressor, pi control, amplitude modulation, Nuclear engineering. Atomic power, TK9001-9401
Abstract

BackgroundShanghai Soft X-ray Free-electron Laser (SXFEL) is upgrading and requires to operate in double-bunch mode instead of original mode to transport uniform energy along the bunch chain.PurposeThis study aims to satisfy the requirement of double-bunch mode by designing and implementing low level radio frequency (LLRF) system to flatten the output of RF pulse compressor through amplitude modulation.MethodsBased on double PI-control loops, the LLRF control system was designed and implemented with one PI-feedback loop for keeping the long-term stability of amplitude and phase, and the additional operating-outside-LLRF PI-feedback loop for flattening the output pulse shape. Furthermore, an experimental setup, including the compressor, was built for the verification of the above method.ResultsThe 2-h continuous test results show that the double PI-control loops can flatten and keep the compressor output, and maintain the long-term stability of amplitude and phase within 0.09% and 0.1° (Root Mean Square, RMS) respectively. In addition, the algorithm can restore the flat-top output automatically when a large manual frequency offset occurs.ConclusionsThe double PI-control loop applied to the LLRF system preserves satisfactory static and dynamic behaviors, meeting the requirement of the SXFEL upgrade.

Published
2022
Full Text
View/download PDF

92. Digital low-level radio frequency system and cavity simulator for 1.3 GHz continuous-wave superconducting radio-frequency cavity

Author

LIU Kui, GU Qiang, ZHANG Junqiang, and ZHAO Minghua

Subjects
digital rf cavity simulator, high-repetition x-ray free-electron laser, low-level rf system, self-excited loop, system generator, Nuclear engineering. Atomic power, TK9001-9401
Abstract

BackgroundA high precision low-level radio-frequency (LLRF) system for a superconducting radio-frequency (RF) cavity of Shanghai high-repetition-rate X-ray free-electron laser and extreme light facility (SHINE) is required to stabilize the electromagnetic field of cavities. However, due to the high loaded quality factor of the 1.3 GHz continuous-wave superconducting RF cavity, the RF cavity has a small electromagnetic bandwidth in the frequency domain. The small electromagnetic frequency mismatch between the RF power source and RF cavity can easily interlock in the generator driven resonator control system.PurposeThis study aims to develope a LLRF and a digital RF cavity simulator ensure stable electromagnetic field of 1.3 GHz continuous-wave superconducting RF cavities.MethodsA self-excited loop (SEL) control system was developed to prevent interlock, and a generator driven resonator (GDR) control system was developed to operate the RF cavity under normal working states. In addition, a digital RF cavity simulator was developed to verify the design algorithms of the LLRF system. The SEL/GDR system and RF cavity simulator were also implemented and tested based on MicroTCA.4 platform.ResultsIn the free SEL mode, the amplitude of the cavity RF field is stable at the set-point, even if the cavity is detuned for several half-bandwidths. In the locked mode, the stability of the cavity RF field in the amplitude and phase are 0.458 0% (Root Mean Square, RMS) and 0.058° (RMS) respectively, at the detuning frequency of 5 Hz.ConclusionsIt is verify that the SEL control system can stabilize the cavity RF field even when the cavity is detuning, and the cavity simulator proves to be a reliable platform for the evaluation of new algorithm.

Published
2021
Full Text
View/download PDF

98. Design and test of a C band local oscillator and clock device in LLRF

Author

XIAO Chengcheng, YIN Zhe, ZHANG Junqiang, and GU Qiang

Subjects
llrf, c band, local oscillator and clock, phase jitter, temperature control, Nuclear engineering. Atomic power, TK9001-9401
Abstract

BackgroundThe linear accelerator of Shanghai soft X-ray free-electron laser facility (SXFEL) operates at 5 712 MHz frequency. In the low level radio frequency (LLRF) system, C band microwave signals were down converted from the 5 686.556 MHz local oscillator (LO) signal to 26.444 MHz intermediate (IM) signal, and then quadruple frequency sampled by the 105.778 MHz clock signal. The stability of LO signal and clock signal can make great influence on the performance of the LLRF system.PurposeThis study aims to design and manufacture a local oscillator and clock device for satisfying the theoretical design requirements of the LLRF in SXFEL.MethodThe LO signal and clock signal were designed to be auto-correlated with the master oscillator signal. All the functional discrete device modules were installed in a shielded aluminum alloy shell, and were matched and interconnected by RF connectors after debugging and testing separately. The phase jitter integral of clock signal and LO signal, as well as the possible temperature sensitive nonlinear modules, i.e., temperature control of frequency divider and frequency multiplier, in clock Lo equipment were experimentally tested.ResultsThe experimental results show that the additional phase jitter integral of LO signal is 21.43 fs, better than the requirement of 40 fs.ConclusionsThe performance of this manufactured LO and clock device can meet the theoretical requirement of the SXFEL.

Published
2021
Full Text
View/download PDF

99. Some estimates of Schrödinger type operators on variable Lebesgue and Hardy spaces

Author

Zhang, Junqiang and Liu, Zongguang

Abstract

In this article, the authors consider the Schrödinger type operator L:=-div(A?)+Von Rnwith n=3, where the matrix Asatisfies uniformly elliptic condition and the nonnegative potential Vbelongs to the reverse Hölder class RHq(Rn)with q?(n/2,8). Let p(·):Rn?(0,8)be a variable exponent function satisfying the globally log-Hölder continuous condition. When p(·):Rn?(1,8), the authors prove that the operators VL-1, V1/2?L-1and ?2L-1are bounded on variable Lebesgue space Lp(·)(Rn). When p(·):Rn?(0,1], the authors introduce the variable Hardy space HLp(·)(Rn), associated to L, and show that VL-1, V1/2?L-1and ?2L-1are bounded from HLp(·)(Rn)to Lp(·)(Rn).

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results