arXiv subjects

Jian Wang

Publications and source records attributed to Jian Wang.

At least 991 records · Page 55Linked to original sources

arXiv2018

Detection of bosonic mode as a signature of magnetic excitation in one unit cell FeSe on SrTiO3

We report an in situ scanning tunneling spectroscopy study of one-unit-cell (1-UC) FeSe film on SrTiO3(001) (STO) substrate. In quasiparticle density of states, bosonic excitation mode characterized by the "dip-hump" structure is detected outside the larger superconducting gap with energy comparable with phonon and spin resonance modes in heavily electron-doped iron selenides. Statistically, the excitation mode, which is intimately correlated with superconductivity, shows an anticorrelation with pairing strength and yields an energy scale upper-bounded by twice the superconducting gap coinciding with the characteristics of magnetic resonance in cuprates and iron-based superconductors. The local response of tunneling spectra to magnetically different Se defects all exhibits the induced in-gap quasiparticle bound states, indicating an unconventional sign-reversing pairing. These results support the magnetic nature of the excitation mode and possibly reveal a signature of electron-magnetic-excitation coupling in high-temperature superconductivity of 1-UC FeSe/STO.

cond-mat.supr-con↗

arXiv2018

Discovery of Log-Periodic Oscillations in Ultra-Quantum Topological Materials

Quantum oscillations are usually the manifestation of the underlying physical nature in condensed matter systems. Here we report a new type of log-periodic quantum oscillations in ultra-quantum three-dimensional topological materials. Beyond the quantum limit (QL), the log-periodic oscillations involving up to five oscillating cycles (5 peaks and 5 dips) are observed on the magnetoresistance (MR) of high quality single-crystal ZrTe5, virtually showing the clearest feature of discrete scale invariance (DSI). Further theoretical analyses show that the two-body quasi-bound states can be responsible for the DSI feature. Our work provides a new perspective on the ground state of topological materials beyond the QL.

cond-mat.mtrl-sci↗

arXiv2018

A Sharp Condition for Exact Support Recovery of Sparse Signals With Orthogonal Matching Pursuit

Support recovery of sparse signals from noisy measurements with orthogonal matching pursuit (OMP) has been extensively studied in the literature. In this paper, we show that for any $K$-sparse signal $\x$, if the sensing matrix $\A$ satisfies the restricted isometry property (RIP) of order $K + 1$ with restricted isometry constant (RIC) $δ_{K+1} < 1/\sqrt {K+1}$, then under some constraint on the minimum magnitude of the nonzero elements of $\x$, the OMP algorithm exactly recovers the support of $\x$ from the measurements $\y=\A\x+\v$ in $K$ iterations, where $\v$ is the noise vector. This condition is sharp in terms of $δ_{K+1}$ since for any given positive integer $K\geq 2$ and any $1/\sqrt{K+1}\leq t<1$, there always exist a $K$-sparse $\x$ and a matrix $\A$ satisfying $δ_{K+1}=t$ for which OMP may fail to recover the signal $\x$ in $K$ iterations. Moreover, the constraint on the minimum magnitude of the nonzero elements of $\x$ is weaker than existing results.

cs.IT↗

arXiv2018

The Turán Number for Spanning Linear Forests

For a set of graphs $\mathcal{F}$, the extremal number $ex(n;\mathcal{F})$ is the maximum number of edges in a graph of order $n$ not containing any subgraph isomorphic to some graph in $\mathcal{F}$. If $\mathcal{F}$ contains a graph on $n$ vertices, then we often call the problem a spanning Turán problem. A linear forest is a graph whose connected components are all paths and isolated vertices. In this paper, we let $\mathcal{L}_n^k$ be the set of all linear forests of order $n$ with at least $n-k+1$ edges. We prove that when $n\geq 3k$ and $k\geq 2$, \[ ex(n;\mathcal{L}_n^k)=\binom{n-k+1}{2}+ O(k^2). \] Clearly, the result is interesting when $k=o(n)$.

math.CO↗

arXiv2018

Fe3O4@astragalus polysaccharide core-shell nanoparticles for iron deficiency anemia therapy and magnetic resonance imaging in vivo

Fe3O4@astragalus polysaccharide core-shell nanoparticles (Fe3O4@APS NPs) were demonstrated to be an efficient therapeutic drug for treating iron deficiency anemia (IDA) in vivo. The Fe3O4@APS NPs have been synthesized using a two steps approach involving hydrothermal synthesis and subsequent esterification. Transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy studies show that APS are attached on the surfaces of the highly monodisperse Fe3O4 NPs. Dynamic light scatting (DLS) and magnetic characterizations reveal that the Fe3O4@APS NPs have outstanding water solubility and stability. Cytotoxicity assessment using Hela cells and pathological tests in mice demonstrate their good biocompatibility and low toxicity. The IDA treatment in rats shows that they have efficient therapeutic effect, which is contributed to both the iron element supplement from Fe3O4 and the APS-stimulated hematopoietic cell generation. Moreover, the Fe3O4@APS NPs are superparamagnetic and thus able to be used for magnetic resonance imaging (MRI). This study has demonstrated the potential of nanocomposites involving purified natural products from Chinese herb medicine for biomedical applications.

physics.bio-ph↗

arXiv2018

Design of Near Infrared Sky Brightness Monitor and Test Running at Ngari Observatory in Tibet

Tibet is known as the third pole of the earth, as high as the South Pole and North Pole. The Ngari (Ali) observatory in Tibet has the advantage of plenty of photometric night, low precipitable water vapor, high transmittance, good seeing. It is a good site, and promising to be one of the best place for infrared and submillimeter observations in the world. However, there is no data available for sky background brightness in such place, which restrict the astronomical development of the sites. In the near infrared band of J, H, Ks, a NIR sky brightness monitor (NISBM) is designed based on InGaAs photoelectric diode. By using the method of chopper modulation and digital lock-in amplifier processing, the SNR (Signal Noise Ratio), detectivity and the data acquisition speed of the device is greatly improved. For each band of J, H, Ks, an independent instrument is designed and calibrated in laboratory. The NISBM has been installed in Ngari observatory in July of 2017 and obtained the first data of NIR sky brightness at Ngari observatory.

astro-ph.IM↗

arXiv2018

The operational and control software of Multi-channel Antarctic Solar Telescope

MARST (Multi-channel Antarctic Solar Telescope) aims to observe the Sun in multiple wavebands in Antarctica and will be China's first solar telescope in Antarctica. The telescope has two tubes, corresponding to Photosphere observation which uses 11 filters and Chromosphere observation in Hα waveband. The two tubes need to be coordinated to observe at the same time. The telescope will observe the Sun for a long time, so a self-guiding module is needed to improve sun tracking. Besides, performing solar specific flat-field exposure is necessary for analyzing. EPICS is introduced to control each hardware and an autonomous observation system based on RTS2 is designed under such demands. EPICS application modules are implemented for each device: telescope mount & focuser, filter wheel, Hα filter, dome with webcams, Andor CCD and PI CCD. We also integrate EPICS modules into RTS2 framework with an XML format configuration. To control these applications autonomously we have developed a RTS2 executor module where two plan classes are instantiated to control two sets of filters and CCDs, and to ensure only one could control the mount at the same time. Different types of observation plans are designed to describe different series of processes with different priorities. To improve sun tracking, we calculate the centroid of each image to get the offset, then apply the correction to the telescope during observation process. For frontend users, a GUI based on PyQt5 and QML is implemented and connects to rts2-httpd and rts2-proxy modules so that users can control devices, check images and get logs.

astro-ph.IM↗

arXiv2018

Development and Characterization of a 3.2 Gb/s Serial Link Transmitter for CMOS Image Sensors in Subatomic Physics Experiments

This paper presents development and characterization of a 3.2 Gb/s serial link transmitter for CMOS image sensors. The transmitter incorporates Reed-Solomon code to achieve low error rate in the harsh environment of subatomic physics experiments. Pre-emphasis is implemented in the transmitter, allowing data transmission over low-mass cables. It is fabricated in a 0.18 $μm$ CMOS image process as a standalone chip to characterize its performance, with the core area of 1.8 $mm^2$. A frame data rate of $3\cdot10^{-12}$ with a confidence level of 94.5$\%$ was measured through an FPGA based receiver. The measured nominal power consumption is 135 mW. The transmitter functions normally after irradiated with 4.5 Mrad TID.

physics.ins-det↗

arXiv2018

Study of Full Parallel RS(31,27) Encoder for a 3.2 Gbps Serial Transmitter in 0.18 um CMOS Technology

This work presents the design of an RS(31,27) Reed Solomon encoder for a 3.2 Gbps serial transmitter in 0.18 um CMOS technology. The proposed encoder is designed with a novel full parallel structure optimized for high speed and high stability. One data frame contains 2 interleaved RS(31,27) codes and thus it can correct at most 20 bits of consecutive errors. A corresponding decoder is implemented on Xilinx Kintex-7 FPGA.

eess.SP↗

arXiv2018

Transient spin current under a thermal switch

In this work, we explore the possibility of enhancing a spin current under a thermal switch, i.e., connecting the central transport region to two leads in individual thermal equilibrium abruptly. Using the nonequilibrium Green's function method for the transient spin current, we obtain a closed-form solution, which is applicable in the whole nonlinear quantum transport regime with a significant reduction of computational complexity. Furthermore, we perform a model calculation on a single-level quantum dot with Lorentzian linewidth. It shows that the transient spin current may vary spatially, causing spin accumulation or depletion in the central region. Moreover, general enhancement of the spin current in the transient regime is observed. In particular, the in-plane components of the transient spin current may increase by 2-3 orders of magnitude compared to the steady-state thermoelectric spin current under a temperature difference of 30 K. Our research demonstrates that ultrafast enhancement of spin currents can be effectively achieved by thermal switches.

cond-mat.mes-hall↗

arXiv2018

A Driver ASIC for Scientific CCD Detectors Using 180nm Technology

In order to achieve the driver function for several types of scientific CCD detector from E2V Co Ltd, and decreasing the size of electronics of CCD detector system, an Application-specified Integrated Circuit (ASIC) was designed. It provides multi-channel clocks and bias voltage for CCD driver. In the ASIC, the clock drivers are made of a clock switch circuit and high voltage amplifier. Two 8-bit current-steering DACs are used to adjust the driver capability and high-level voltage of clocks. The bias drivers are generated by 8-bit current-steering DACs and off-chip operation amplifiers. The Global Foundry 180 nm BCDlite technology is selected to implement this design. The first version of design has been finished and the tests have been done.

physics.ins-det↗

arXiv2018

A programmable clock generator for automatic Quality Assurance of LOCx2

The upgrade of ATLAS Liquid Argon Calorimeter (LAr) Phase-1 trigger requires high-speed, low-latency data transmission to read out the Lar Trigger Digitizer Board (LTDB). A dual-channel transmitter ASIC LOCx2 have been designed and produced. In order to ensure all the LOCx2 chips behave properly, a Quality Assurance needs to be conducted before assembly. The problem I was trying to solve in this project is to yield a clock signal with continuously adjustable frequency and phase offset to generate and control an eye diagram for the QA. By configuring the registers of an any-frequency generator IC, Si5338, the clock signal whose frequency range from 5MHz to 200 MHz have been properly produced. For the purpose of further development, a C-language based DLL which packs up the function of adjusting frequency and setting phase offset was designed and built, and several evaluation was performed to ensure the robustness of DLL.

eess.SP↗

arXiv2018

Design of a Non-vacuum-cooling Compact Scientific CCD Camera

CCD was born in Bell Laboratories in 1969 and has been widely used in various fields. Its ultra-low noise and high quantum efficiency make it work well in particle physics, high energy physics, nuclear physics and astrophysics. Nowadays, more and more CCD cameras have been developed for medical diagnosis, scientific experiments, aerospace, military exploration and other fields. For the wide range of CCD cameras, a Non-vacuum-cooling compact (NVCC) scientific CCD camera has been developed, including FPGA-based low noise clock and bias driver circuit, data acquisition circuit, STM32-based temperature control design. At the same time, the readout noise of the imaging system is studied emphatically. The scheme to generate the CCD clock and the bias driving circuit through ultralow noise LDOs is proposed. The camera was tested in a variety of environments, and the test results show that the system can run at a maximum rate of 5M pixels/s and readout noise is as low as 9.29e^- when the CCD readout speed is 500K pixels/s. Finally, a series of stability tests were carried out on the camera system.

physics.ins-det↗

arXiv2018

Detection of Weak Near-Infrared Signal Based on Digital Orthogonal Vector Lock-in Amplifier

A near-infrared (NIR) measurement based on digital orthogonal vector lock-in amplifier (LIA) is present in this paper. NIR sky background radiation is very weak. To detect the signals obscured by noise, the best way achieved is to use a chopper to modulate the detected signal and using a LIA to demodulate. The effect of 1/f noise of detector, dark current and other noises can be reduced to get sufficient signal-to-noise ratio (SNR). The orthogonal vector LIA can avoid the phase shift on the accuracy of measurement by two orthogonal components. In order to simplify the system, a digital algorithm is adopted to realize the LIA which is operated in a microcontroller with ARM cortex-M4. Data is obtained through ADC and the signal of detector is amplified and filtered. Then the phase sensitive detection (PSD), low-pass filter (LPF) and amplitude phase calculation are performed. The digital method can greatly simplify the circuit, and conveniently adjust the time constant of the LPF to realize the different equivalent noise bandwidth (ENB). The algorithm has the specification of high precision, flexible usage, simple implementation and low computation resource. By using this method, the weak infrared signal submerged by the noise can be obtained, which extremely improves the detection capability of the system.

astro-ph.IM↗

arXiv2018

Think Visually: Question Answering through Virtual Imagery

In this paper, we study the problem of geometric reasoning in the context of question-answering. We introduce Dynamic Spatial Memory Network (DSMN), a new deep network architecture designed for answering questions that admit latent visual representations. DSMN learns to generate and reason over such representations. Further, we propose two synthetic benchmarks, FloorPlanQA and ShapeIntersection, to evaluate the geometric reasoning capability of QA systems. Experimental results validate the effectiveness of our proposed DSMN for visual thinking tasks.

cs.CL↗

arXiv2018

Fully Differential Higgs Pair Production in Association With a $Z$ Boson at Next-to-Next-to-Leading Order in QCD

We present a fully differential next-to-next-to-leading order calculation of the Higgs pair production in association with a $Z$ boson, which is important for probing the trilinear Higgs self-coupling. The next-to-next-to-leading-order corrections enhance the next-to-leading order total cross sections by a factor of $1.2\sim 1.5$, depending on the collider energy, and change the shape of next-to-leading order kinematic distributions. We discuss how to determine the trilinear Higgs self-coupling using our results.

hep-ph↗

arXiv2018

Conic singularities metrics with prescribed scalar curvature: a priori estimates for normal crossing divisors

The purpose of this paper is to prove the a priori estimates for constant scalar curvature Kaehler metrics with conic singularities along normal crossing divisors. The zero order estimates are proved by a reformulated version of Alexandrov's maximum principle. The higher order estimates follow from Chen-Cheng's frame work, equipped with new techniques to handle the singularities. Finally, we extend these estimates to the twisted equations.

math.DG↗

arXiv2018

Refined basic couplings and Wasserstein-type distances for SDEs with Lévy noises

We establish the exponential convergence with respect to the $L^1$-Wasserstein distance and the total variation for the semigroup corresponding to the stochastic differential equation (SDE) $$d X_t=d Z_t+b(X_t)\,d t,$$ where $(Z_t)_{t\ge0}$ is a pure jump Lévy process whose Lévy measure $ν$ fulfills $$ \inf_{x\in \R^d, |x|\le κ_0} [ν\wedge (δ_x \ast ν)]( \R^d)>0$$ for some constant $κ_0>0$, and the drift term $b$ satisfies that for any $x,y\in \R^d$, $$\langle b(x)-b(y),x-y\rangle\le \begin{cases} Φ_1(|x-y|)|x-y|,& |x-y|\le l_0; -K_2|x-y|^2,& |x-y|> l_0 \end{cases}$$ with some positive constants $K_2, l_0$ and positive measurable function $Φ_1$. The method is based on the refined basic coupling for Lévy jump processes. As a byproduct, we obtain sufficient conditions for the strong ergodicity of the process $(X_t)_{t\ge0}$.

math.PR↗