arXiv subjects

Ping Yang

Publications and source records attributed to Ping Yang.

At least 91 records · Page 5Linked to original sources

arXiv2022

Symmetrical Z-Complementary Code Sets (SZCCSs) for Optimal Training in Generalized Spatial Modulation

This paper introduces a novel class of code sets, called "symmetrical Z-complementary code sets (SZCCSs)" , whose aperiodic auto- and cross- correlation sums exhibit zero-correlation zones (ZCZs) at both the front-end and tail-end of the entire correlation window. Three constructions of (optimal) SZCCSs based on general Boolean functions are presented. As a second major contribution, we apply SZCCSs to design optimal training sequences for broadband generalized spatial modulation (GSM) systems over frequency-selective channels. Key words: Complementary code set, channel estimation, training sequence design, generalized spatial modulation, frequency-selective channels.

cs.IT↗

arXiv2022

Topmetal-M: a novel pixel sensor for compact tracking applications

The Topmetal-M is a large area pixel sensor (18 mm * 23 mm) prototype fabricated in a new 130 nm high-resistivity CMOS process in 2019. It contains 400 rows * 512 columns square pixels with the pitch of 40 μm. In Topmetal-M, a novel charge collection method combing the Monolithic Active Pixel Sensor (MAPS) and the Topmetal sensor has been proposed for the first time. Both the ionized charge deposited by the particle in the sensor and along the track over the sensor can be collected. The in-pixel circuit mainly consists of a low-noise charge sensitive amplifier to establish the signal for the energy reconstruction, and a discriminator with a Time-to-Amplitude Converter (TAC) for the Time of Arrival (TOA) measurement. With this mechanism, the trajectory, particle hit position, energy and arrival time of the particle can be measured. The analog signal from each pixel is accessible through time-shared multiplexing over the entire pixel array. This paper will discuss the design and preliminary test results of the Topmetal-M sensor.

physics.ins-det↗

arXiv2022

Approximate the individually fair k-center with outliers

In this paper, we propose and investigate the individually fair $k$-center with outliers (IF$k$CO). In the IF$k$CO, we are given an $n$-sized vertex set in a metric space, as well as integers $k$ and $q$. At most $k$ vertices can be selected as the centers and at most $q$ vertices can be selected as the outliers. The centers are selected to serve all the not-an-outlier (i.e., served) vertices. The so-called individual fairness constraint restricts that every served vertex must have a selected center not too far way. More precisely, it is supposed that there exists at least one center among its $\lceil (n-q) / k \rceil$ closest neighbors for every served vertex. Because every center serves $(n-q) / k$ vertices on the average. The objective is to select centers and outliers, assign every served vertex to some center, so as to minimize the maximum fairness ratio over all served vertices, where the fairness ratio of a vertex is defined as the ratio between its distance with the assigned center and its distance with a $\lceil (n - q )/k \rceil_{\rm th}$ closest neighbor. As our main contribution, a 4-approximation algorithm is presented, based on which we develop an improved algorithm from a practical perspective.

cs.DS↗

arXiv2021

Radiative Transfer Modeling of An SN 1987A Light Echo$-$AT2019xis

We use a Monte Carlo radiative transfer model (MCRTM) to simulate the UBVRI light curves, images and linear polarization of a light echo from supernova SN$~$1987A in the Large Magellanic Cloud (LMC) using various dust cloud shapes, sizes, and optical properties. We compare the theoretical simulations to the observations of AT2019xis, a light echo detected at a large angular distance (4.05$^{'}$) from SN$~$1987A. We estimate the size and optical thickness of the dust cloud based on the simulation results and the observations of Optical Gravitational Lensing Experiment (OGLE-IV) Transient Detection System (OTDS) I-band light curve. The mass of the dust cloud is calculated using the estimated size, optical thickness and extinction coefficient. If the dust cloud is assumed to correspond to a gas-to-dust ratio of 300, the total mass of the dust cloud is approximately 7.8-9.3 $M_{\odot}$. Based on these theoretical models, we show that the morphological shapes of the light echoes in the wavelength range in or shorter than the U-band to be very different from those in the longer wavelength bands, and the difference carries important information on the early UV radiation of SN$~$1987A.

astro-ph.HE↗

arXiv2020

Phase diagram and superconducting dome of infinite-layer $\mathrm{Nd_{1-x}Sr_{x}NiO_{2}}$ thin films

Infinite-layer Nd1-xSrxNiO2 thin films with Sr doping level x from 0.08 to 0.3 were synthesized and investigated. We found a superconducting dome to be between 0.12 and 0.235 which is accompanied by a weakly insulating behaviour in both underdoped and overdoped regimes. The dome is akin to that in the electron-doped 214-type and infinite-layer cuprate superconductors. For x higher than 0.18, the normal state Hall coefficient ($R_{H}$) changes the sign from negative to positive as the temperature decreases. The temperature of the sign changes monotonically decreases with decreasing x from the overdoped side and approaches the superconducting dome at the mid-point, suggesting a reconstruction of the Fermi surface as the dopant concentration changes across the center of the dome.

cond-mat.supr-con↗

arXiv2020

Ultra-Slow Dynamic Annealing of Neutron-induced Defects in n-type Silicon: Role of Charge Carriers

Neutron bombardments with equivalent fluence (1$\times$10$^{10}$ cm$^{-2}$) and different fluxes ($2.5\times$10$^5$ cm$^{-2}$s$^{-1}$ to $1\times$10$^7$ cm$^{-2}$s$^{-1}$) have been performed on three kinds of bipolar devices with n-type silicon as active regions. The measured increase of base currents and input bias currents are found to decrease with increasing neutron flux, implying that the strength of the dynamic annealing of divacancy defects in n-type silicon follows a positive flux dependence. Such a flux dependence is the same as that observed in ions implantation using protons, but the evident flux sensitivity in our experiment is 4 orders of magnitude lower than that of proton bombardment, despite the similarity in the masses and energies of the two particles. The huge discrepancy of flux range is attributed to the presence of vast charge carriers in proton bombardments, which strongly accelerate the dynamic annealing of defects by enhancing the diffusion velocity of Si interstitials and dissociation rate of defect clusters. Our work would contribute to the understanding of the defect annealing processes in silicon.

cond-mat.mtrl-sci↗

arXiv2020

Magnetic asymmetry induced anomalous spin-orbit torque in IrMn

We demonstrate an anomalous spin-orbit torque induced by the broken magnetic symmetry in the antiferromagnet IrMn. We study the magnetic structure of three phases of IrMn thin films using neutron diffraction technique. The magnetic mirror symmetry M' is broken laterally in both L10-IrMn and L12-IrMn3 but not γ-IrMn3. We observe an out-of-plane damping-like spin-orbit torque in both L10-IrMn/permalloy and L12-IrMn3/permalloy bilayers but not in γ-IrMn3/permalloy. This is consistent with both the symmetry analysis on the effects of a broken M' on spin-orbit torque and the theoretical predictions of the spin Hall effect and the Rashba-Edelstein effect. In addition, the measured spin-orbit torque efficiencies are 0.61+-0.01, 1.01+-0.03 and 0.80+-0.01 for the L10, L12 and γ phases, respectively. Our work highlights the critical roles of the magnetic asymmetry in spin-orbit torque generation.

cond-mat.mtrl-sci↗

arXiv2020

Probing the Tavis-Cummings level splitting with intermediate-scale superconducting circuits

We demonstrate the local control of up to eight two-level systems interacting strongly with a microwave cavity. Following calibration, the frequency of each individual two-level system (qubit) is tunable without influencing the others. Bringing the qubits one by one on resonance with the cavity, we observe the collective coupling strength of the qubit ensemble. The splitting scales up with the square root of the number of the qubits, which is the hallmark of the Tavis-Cummings model. The local control circuitry causes a bypass shunting the resonator, and a Fano interference in the microwave readout, whose contribution can be calibrated away to recover the pure cavity spectrum. The simulator's attainable size of dressed states with up to five qubits is limited by reduced signal visibility, and -- if uncalibrated -- by off-resonance shifts of sub-components. Our work demonstrates control and readout of quantum coherent mesoscopic multi-qubit system of intermediate scale under conditions of noise.

quant-ph↗

arXiv2020

Domain structures and the transitional state of ordering in long-period stacking ordered (LPSO) structures in Mg-Al-Gd alloy

The transitional state of ordering in the long-period stacking ordered (LPSO) structure in Mg-Al-Gd alloy has been investigated by scanning transmission electron microscopy. It is found that the domains are the origin of observed transitional state. Three new patterns of clusters at this state can be fully explained by the superimposition of L12 type clusters located in different domains. The domains are further verified by different tilted views. Growth of preferred domains during ageing process will result in final ordered LPSO structure. Based on the idea of domains, less ordered LPSO structure in other dilute alloys can be also understood.

cond-mat.mtrl-sci↗

arXiv2020

Strain self-accommodation during growth of 14H type long-period stacking ordered (LPSO) structures in Mg-Zn-Gd alloy

Cooperative growth of the structure units (SUs) in a 14H type long-period stacking ordered (LPSO) structure has been observed, and there is no obvious accumulation of transformation strain at the growth fronts. The atomic structures at this front are further characterized by Cs-corrected scanning transmission electron microscopy, and the partial dislocations associated SUs are uniquely defined based on the observations at different zone axes. It is found that the Burgers vectors of neighbouring partials are alternatively opposed so that the transformation strain is self-accommodated. Furthermore, this self-accommodation mechanism is rationalized by the elastic interaction energy for combinations of different partials.

cond-mat.mtrl-sci↗

arXiv2020

Image Denoising Using Sparsifying Transform Learning and Weighted Singular Values Minimization

In image denoising (IDN) processing, the low-rank property is usually considered as an important image prior. As a convex relaxation approximation of low rank, nuclear norm based algorithms and their variants have attracted significant attention. These algorithms can be collectively called image domain based methods, whose common drawback is the requirement of great number of iterations for some acceptable solution. Meanwhile, the sparsity of images in a certain transform domain has also been exploited in image denoising problems. Sparsity transform learning algorithms can achieve extremely fast computations as well as desirable performance. By taking both advantages of image domain and transform domain in a general framework, we propose a sparsity transform learning and weighted singular values minimization method (STLWSM) for IDN problems. The proposed method can make full use of the preponderance of both domains. For solving the non-convex cost function, we also present an efficient alternative solution for acceleration. Experimental results show that the proposed STLWSM achieves improvement both visually and quantitatively with a large margin over state-of-the-art approaches based on an alternatively single domain. It also needs much less iteration than all the image domain algorithms.

eess.IV↗

arXiv2020

Cross Z-Complementary Pairs for Optimal Training in Spatial Modulation over Frequency Selective Channels

The contributions of this paper are twofold: Firstly, we introduce a novel class of sequence pairs, called "cross Z-complementary pairs (CZCPs)", each displaying zero-correlation zone (ZCZ) properties for both their aperiodic autocorrelation sums and crosscorrelation sums. Systematic constructions of perfect CZCPs based on selected Golay complementary pairs (GCPs) are presented. Secondly, we point out that CZCPs can be utilized as a key component in designing training sequences for broadband spatial modulation (SM) systems. We show that our proposed SM training sequences derived from CZCPs lead to optimal channel estimation performance over frequency-selective channels.

cs.IT↗

arXiv2019

Resonance inversion in a superconducting cavity coupled to artificial atoms and a microwave background

We demonstrate how heating of an environment can invert the line shape of a driven cavity. We consider a superconducting coplanar cavity coupled to multiple artificial atoms. The measured cavity transmission is characterized by Fano-type resonances with a shape that is continuously tunable by bias current through nearby (magnetic flux) control lines. In particular, the same dispersive shift of the microwave cavity can be observed as a peak or a dip. We find that this Fano-peak inversion is possible due to a tunable interference between a microwave transmission through a background, with reactive and dissipative properties, and through the cavity, affected by bias-current induced heating. The background transmission occurs due to crosstalk between the control and transmission lines. We show how such background can be accounted for by Jaynes-Cummings type models via modified boundary conditions between the cavity and transmission lines. We find generally that whereas resonance positions determine system energy levels, resonance shapes give information on system fluctuations and dissipation.

cond-mat.mes-hall↗

arXiv2019

Controllable Defect Driven Symmetry Change and Domain Structure Evolution in BiFeO3 with Enhanced Tetragonality

Defect engineering has been a powerful tool to enable the creation of exotic phases and the discovery of intriguing phenomena in ferroelectric oxides. However, accurate control the concentration of defects remains a big challenge. In this work, ion implantation, that can provide controllable point defects, allows us the ability to produce a controlled defect-driven true super-tetragonal (T) phase with enhanced tetragonality in ferroelectric BiFeO3 thin films. This point defect engineering is found to drive the phase transition from the as-grown mixed rhombohedral-like (R) and tetragonal-like (MC) phase to true tetragonal (T) symmetry. By further increasing the injected dose of He ion, we demonstrate an enhanced tetragonality super-tetragonal (super-T) phase with the largest c/a ratio (~ 1.3) that has ever been experimentally achieved in BiFeO3. A combination of morphology change and domain evolution further confirm that the mixed R/MC phase structure transforms to the single-domain-state true tetragonal phase. Moreover, the re-emergence of R phase and in-plane stripe nanodomains after heat treatment reveal the memory effect and reversible phase transition. Our findings demonstrate the control of R-Mc-T-super T symmetry changes and the creation of true T phase BiFeO3 with enhanced tetragonality through controllable defect engineering. This work also provides a pathway to generate large tetragonality (or c/a ratio) that could be extended to other ferroelectric material systems (such as PbTiO3, BaTiO3 and HfO2) which may lead to strong polarization enhancement.

cond-mat.mtrl-sci↗

arXiv2018

Thickness-dependent self-polarization-induced intrinsic magnetoelectric effects in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 heterostructures

The self-polarization of PbZr0.52Ti0.48O3 thin film is switched by changing film thickness through the competition between the strain relaxation-induced flexoelectric fields and the interfacial effects. Without an applied electric field, this reversal of self-polarization is exploited to control the magnetic properties of La0.67Sr0.33MnO3 by the competition/cooperation between the charge-mediated and the strain-mediated effects. Scanning transmission electron microscopy, polarized near edge x-ray absorption spectroscopy, and half-integer diffraction measurements are employed to decode this intrinsic magnetoelectric effects in La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 heterostructures. With PbZr0.52Ti0.48O3 films < 48 nm, the self-polarization-driven carrier density modulation around La0.67Sr0.33MnO3/PbZr0.52Ti0.48O3 interface and the strain-mediated Mn 3d orbital occupancy work together to enhance magnetism of 14 unit cells La0.67Sr0.33MnO3 film; with PbZr0.52Ti0.48O3 layers > 48 nm, the strain-induced the change of bond length/angle of MnO6 accompanied with a modified spin configuration are responsible for the decrease in Curie temperature and magnetization of 14 unit cells La0.67Sr0.33MnO3 film.

cond-mat.mtrl-sci↗

arXiv2018

Study of the solute clusters/enrichment at early stage of ageing in Mg-Zn-Gd alloys by atom probe tomography

The chemical enrichment/ordering of solute atoms in Mg matrix are crucial to understand the formation mechanism of long-period stacking ordered (LPSO) structures. In this study, three-dimensional distribution of solute elements in an Mg-Zn-Gd alloy during ageing process is quantitatively characterized by three-dimensional atom probe (3DAP) tomography. Based on the radius distribution function, it is found that Zn-Gd solute pairs in Mg matrix appear mainly in two peaks at early stage of ageing and the separation distance between Zn and Gd atoms is well rationalized by the first-principles calculation. Moreover, the fraction of Zn-Gd solute pairs increases first and decreases subsequently due to the precipitation of LPSO structures. Moreover, the composition of structural unit in LPSO structure and the solute enrichment around it are quantified. It is found that Zn and Gd elements are synchronized in the LPSO structure, and solute segregation of pure Zn or Gd is not observed at the transformation front of the LPSO structure in this alloy. In addition, the crystallography of transformation front is further determined by 3DAP data.

cond-mat.mtrl-sci↗

arXiv2018

Comments on 'Revisiting building block ordering of long-period stacking ordered structures in Mg-Y-Al alloys'

In a recent paper, Zhang et al. [Acta Materialia 152 (2018) 96] studied the in-plane ordering of the long-period stacking ordered (LPSO) structure in Mg-Al-Y alloys. In addition to the well-known L12 type building cluster, they proposed three new types of metastable building clusters. However, we will show that these new types of building clusters are caused by the superimposition of L12 type clusters located in different domains. In addition, the experimental evidence for domain structures in a similar alloy system Mg-Al-Gd is provided.

cond-mat.mtrl-sci↗

arXiv2018

Asymmetrical precipitation on {10-12} twin boundary in magnesium alloy

Precipitation on deformation defects is essential for enhancing mechanical properties of age-hardenable alloys. {10-12} twinning is common in deformed alloys with hexagonal-close-packed structure. In this work, we revealed how {10-12} twin boundary (TB) influences beta-Mg17Al12 precipitation in Mg-9Al-1Zn alloy. The precipitates on the TB are rod-like, while others are lath-shape. The precipitates hold the Burgers orientation relationship (OR) only with twin or matrix, contrary to traditional wisdom in others alloys that precipitates on TB symmetrically keep an OR with both twin and matrix. Moreover, certain precipitate variants are absent, and a new rule for variant selection on TB is proposed.

cond-mat.mtrl-sci↗