arXiv subjects

Y. Liu

Publications and source records attributed to Y. Liu.

At least 217 records · Page 12Linked to original sources

arXiv2022

Optimal Repair/Access MDS Array Codes with Multiple Repair Degrees

In the literature, most of the known high-rate $(n,k)$ MDS array codes with the optimal repair property only support a single repair degree (i.e., the number of helper nodes contacted during a repair process) $d$, where $k\le d\le n-1$. However, in practical storage systems, the number of available nodes changes frequently. Thus, it is preferred to construct $(n,k)$ MDS array codes with multiple repair degrees and the optimal repair property for all nodes. To the best of our knowledge, only two MDS array codes have such properties in the literature, which were proposed by Ye and Barg (IEEE Trans. Inform. Theory, 63(10), 2001-2014, 2017). However, their sub-packetization levels are relatively large. In this paper, we present a generic construction method that can convert some MDS array codes with a single repair degree into the ones with multiple repair degrees and optimal repair property for a set of nodes, while the repair efficiency/degrees of the remaining nodes can be kept. As an application of the generic construction method, an explicit construction of high-rate MDS array code with multiple repair degrees and the optimal access property for all nodes is obtained over a small finite field. Especially, the sub-packetization level is much smaller than that of the two codes proposed by Ye and Barg concerning the same parameters $n$ and $k$.

cs.IT↗

arXiv2022

Effective Field Theory Analysis of CDMSlite Run 2 Data

CDMSlite Run 2 was a search for weakly interacting massive particles (WIMPs) with a cryogenic 600 g Ge detector operated in a high-voltage mode to optimize sensitivity to WIMPs of relatively low mass from 2 - 20 GeV/$c^2$. In this article, we present an effective field theory (EFT) analysis of the CDMSlite Run 2 data using an extended energy range and a comprehensive treatment of the expected background. A binned likelihood Bayesian analysis was performed on the recoil energy data, taking into account the parameters of the EFT interactions and optimizing the data selection with respect to the dominant background components. Energy regions within 5$σ$ of known activation peaks were removed from the analysis. The Bayesian evidences resulting from the different operator hypotheses show that the CDMSlite Run 2 data are consistent with the background-only models and do not allow for a signal interpretation assuming any additional EFT interaction. Consequently, upper limits on the WIMP mass and coupling-coefficient amplitudes and phases are presented for each EFT operator. These limits improve previous CDMSlite Run 2 bounds for WIMP masses above 5 GeV/$c^2$.

astro-ph.CO↗

arXiv2022

Spin-wave-driven skyrmion dynamics in ferrimagnets: Effect of net angular momentum

Searching for low-power-consuming and high-efficient methods for well controllable driving of skyrmion motion is one of the most concerned issues for future spintronic applications, raising high concern with an appreciated choice of magnetic media and driving scenario. In this work, we propose a novel scenario of spin wave driven skyrmion motion in a ferrimagnetic (FiM) lattice with the net angular momentum δs. We investigate theoretically the effect of both δs and the circular polarization of spin wave on the skyrmion dynamics. It is revealed that the momentum onto the skyrmion imposed by the excited spin wave can be partitioned into a ferromagnetic term plus an antiferromagnetic term. The ratio of these two terms and consequently the Hall angle of skyrmion motion can be formulated as the functions of δs, demonstrating the key role of δs as an effective control-parameter for the skyrmion motion. Moreover, the spin wave frequency dependent skyrmion motion is discussed, predicting the frequency enhanced skyrmion Hall motion. This work thus represents an essential contribution to understand the skyrmion dynamics in a FiM lattice.

physics.app-ph↗

arXiv2022

Toward CUPID-1T

Current experiments to search for broken lepton-number symmetry through the observation of neutrinoless double-beta decay ($0\mathrm{νββ}$) provide the most stringent limits on the Majorana nature of neutrinos and the effective Majorana neutrino mass ($m_{ββ}$). The next-generation experiments will focus on the sensitivity to the $0\mathrm{νββ}$ half-life of $\mathcal{O}(10^{27}$--$10^{28}$~years$)$ and $m_{ββ}\lesssim15$~meV, which would provide complete coverage of the so-called Inverted Ordering region of the neutrino mass parameter space. By taking advantage of recent technological breakthroughs, new, future calorimetric experiments at the 1-ton scale can increase the sensitivity by at least another order of magnitude, exploring the large fraction of the parameter space that corresponds to the Normal neutrino mass ordering. In case of a discovery, such experiments could provide important insights toward a new understanding of the mechanism of $0\mathrm{νββ}$. We present here a series of projects underway that will provide advancements in background reduction, cryogenic readout, and physics searches beyond $0\mathrm{νββ}$, all moving toward the next-to-next generation CUPID-1T detector.

nucl-ex↗

arXiv2022

Scintillator Tile Batch Test of CEPC AHCAL

Hadron calorimeter (HCAL) is an essential sub-detector of the baseline detector system for Circular Electron Positron Collider (CEPC). We plan to build an Analog Hadron CALorimeter (AHCAL) prototype based on the Particle Flow Algorithm (PFA). The AHCAL of CEPC uses steel as absorber and scintillator tiles read out by Silicon Photo-Multipliers (SiPMs) as sensitive medium. The energy linearity and resolution of the calorimeter depends on the light yield uniformity of sensitive medium. It is essential to qualify the entire detector production in order to select scintillator tiles with light yield uniform within 10\%. An automated batch test platform has been designed with 144 channels, an automated 3D servo motor. The paper summarizes the tests performed on more than 15000 scintillator tiles. The measured light yield, corrected for the set-up response non-uniformity, is around 12.9 p.e. . About 91.6\% of scintillators (14219 pieces) are qualified within 10\% of light yield window.

physics.ins-det↗

arXiv2022

Studies of the Earth shielding effect to direct dark matter searches at the China Jinping Underground Laboratory

Dark matter direct detection experiments mostly operate at deep underground laboratories. It is necessary to consider shielding effect of the Earth, especially for dark matter particles interacting with a large cross section. We analyzed and simulated the Earth shielding effect for dark matter at the China Jinping Underground Laboratory (CJPL) with a simulation package, CJPL Earth Shielding Simulation code (CJPL\_ESS), which is applicable to other underground locations. The further constraints on the $χ$-N cross section exclusion regions are derived based on the studies with CDEX experiment data.

hep-ex↗

arXiv2022

Magnetic helicity and energy of emerging solar active regions and their erruptivity

Aims. We investigate the role of the accumulation of both magnetic helicity and magnetic energy in the generation of coronal mass ejections (CMEs) from emerging solar active regions (ARs). Methods. Using vector magnetic field data obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we calculate the magnetic helicity and magnetic energy injection rates as well as the resulting accumulated budgets in 52 emerging ARs from the start time of magnetic flux emergence until they reach heliographic longitude of 45$^{\circ}$ West (W45). Results. Seven of the ARs produced CMEs while 45 did not. In a statistical sense, the eruptive ARs accumulate larger budgets of both magnetic helicity and energy than the noneruptive ones over intervals that start from flux emergence start time and end (i) at the end of flux emergence phase, and (ii) when the AR produces its first CME or crosses W45, whichever happens first. We found magnetic helicity and energy thresholds of $9 \times 10^{41}$ Mx$^2$ and $2 \times 10^{32}$ erg, respectively, which, if crossed, ARs are likely to erupt. The segregation, in terms of accumulated magnetic helicity and energy budgets, of the eruptive ARs from the noneruptive ones is violated in one case when an AR erupts early in its emergence phase and in six cases with noneruptive ARs exhibiting large magnetic helicity and energy budgets. Decay index calculations may indicate that these ARs did not erupt because the overlying magnetic field provided stronger or more extended confinement than in eruptive ARs. Conclusions. Our results indicate that emerging ARs tend to produce CMEs when they accumulate significant budgets of both magnetic helicity and energy. Any study of their eruptive potential should place magnetic helicity on equal footing with magnetic energy.

astro-ph.SR↗

arXiv2022

Optimization of the first CUPID detector module

CUPID will be a next generation experiment searching for the neutrinoless double $β$ decay, whose discovery would establish the Majorana nature of the neutrino. Based on the experience achieved with the CUORE experiment, presently taking data at LNGS, CUPID aims to reach a background free environment by means of scintillating Li$_{2}$$^{100}$MoO$_4$ crystals coupled to light detectors. Indeed, the simultaneous heat and light detection allows us to reject the dominant background of $α$ particles, as proven by the CUPID-0 and CUPID-Mo demonstrators. In this work we present the results of the first test of the CUPID baseline module. In particular, we propose a new optimized detector structure and light sensors design to enhance the engineering and the light collection, respectively. We characterized the heat detectors, achieving an energy resolution of (5.9 $\pm$ 0.2) keV FWHM at the $Q$-value of $^{100}$Mo (about 3034 keV). We studied the light collection of the baseline CUPID design with respect to an alternative configuration which features gravity-assisted light detectors' mounting. In both cases we obtained an improvement in the light collection with respect to past measures and we validated the particle identification capability of the detector, which ensures an $α$ particle rejection higher than 99.9%, fully satisfying the requirements for CUPID.

physics.ins-det↗

arXiv2022

Observation of the $π^2σ^2$-bond linear-chain molecular structure in $^{16}$C

Measurements of the $^2$H($^{16}$C,$^{16}$C$^{*}$$\rightarrow^4$He+$^{12}$Be or $^6$He+$^{10}$Be)$^2$H inelastic excitation and cluster-decay reactions have been carried out at a beam energy of about 23.5 MeV/u. A specially designed detection system, including one multi-layer silicon-strip telescope at around zero degrees, has allowed the high-efficiency three-fold coincident detection and therefore the event-by-event determination of the energy of the unstable nucleus beam. The decay paths from the $^{16}$C resonances to various states of the final $^{10}$Be or $^{12}$Be nucleus are recognized thanks to the well-resolved $Q$-value spectra. The reconstructed resonances at 16.5(1), 17.3(2), 19.4(1) and 21.6(2) MeV are assigned as the $0^+$, $2^+$, $4^+$ and $6^+$ members, respectively, of the positive-parity $(3/2_π^-)^2(1/2_σ^-)^2$-bond linear-chain molecular band in $^{16}$C, based on the angular correlation analysis for the 16.5 MeV state and the excellent agreement of decay patterns between the measurements and theoretical predictions. Moreover, another intriguing high-lying state was observed at 27.2(1) MeV which decays almost exclusively to the $\sim$6 MeV states of $^{10}$Be, in line with the newly predicted pure $σ$-bond linear-chain configuration.

nucl-ex↗

arXiv2022

Characterization of photoinduced normal state through charge density wave in superconducting YBa$_2$Cu$_3$O$_{6.67}$

The normal state of high-Tc cuprates has been considered one of the essential topics in high-temperature superconductivity research. However, compared to the high magnetic fields study of it, understanding a photoinduced normal state remains elusive. Here, we explore a photoinduced normal state of YBa$_2$Cu$_3$O$_{6.67}$ (YBCO) through a charge density wave (CDW) with time-resolved resonant soft x-ray scattering, as well as a high-magnetic field x-ray scattering. In the non-equilibrium state in which people predict a quenched superconducting state based on the previous optical spectroscopies, we experimentally observed a similar analogy to the competition between superconductivity and CDW shown in the equilibrium state. We further observe that the broken pairing states in the superconducting CuO$_2$ plane via the optical pump lead to nucleation of three-dimensional CDW precursor correlation, revealing that the photoinduced CDW is similar to phenomena shown under magnetic fields. Ultimately, these findings provide a critical clue that the characteristics of the photoinduced normal state show a solid resemblance to those under magnetic fields in equilibrium conditions.

cond-mat.supr-con↗

arXiv2022

Evidence for spin-polarized bound states in semiconductor-superconductor-ferromagnetic insulator islands

We report Coulomb blockade transport studies of semiconducting InAs nanowires grown with epitaxial superconducting Al and ferromagnetic insulator EuS on overlapping facets. Comparing experiment to a theoretical model, we associate cotunneling features in even-odd bias spectra with spin-polarized Andreev levels. Results are consistent with zero-field spin splitting exceeding the induced superconducting gap. Energies of subgap states are tunable on either side of zero via electrostatic gates.

cond-mat.mes-hall↗

arXiv2022

KCo$_2$As$_2$: A New Portal for the Physics of High-Purity Metals

High-quality single crystals of KCo$_2$As$_2$ with the body-centered tetragonal ThCr$_2$Si$_2$ structure were grown using KAs self flux. Structural, magnetic, thermal, and electrical transport were investigated. No clear evidence for any phase transitions was found in the temperature range 2 to 300 K. The in-plane electrical resistivity $ρ$ versus temperature $T$ is highly unusual, showing a $T^4$ behavior below 30 K and an anomalous positive curvature up to 300 K which is different from the linear behavior expected from the Bloch-Grüneisen theory for electron scattering by acoustic phonons. This positive curvature has been previously observed in the in-plane resistivity of high-conductivity layered delafossites such as PdCoO$_2$ and PtCoO$_2$. The in-plane $ρ(T\to0) = 0.36~μΩ$ cm of KCo$_2$As$_2$ is exceptionally small for this class of compounds. The material also exhibits a nearly linear magnetoresistance at low $T$ which attains a value of about 40% at $T=2$K and magnetic field $H= 80$ kOe. The magnetic susceptibility $χ$ of KCo$_2$As$_2$ is isotropic and about an order of magnitude smaller than the values for the related compounds SrCo$_2$As$_2$ and BaCo$_2$As$_2$. The $χ$ increases above 100 K which is found from our first-principles calculations to arise from a sharp peak in the electronic density of states just above the Fermi energy $E_{\rm F}$. Heat capacity $C_{\rm p}(T)$ data at low $T$ yield an electronic density of states $N(E_{\rm F})$ that is about 36% larger than predicted by the first-principles theory. The $C_{\rm p}(T)$ data near room temperature suggest the presence of excited optic vibration modes which may also be the source of the positive curvature in $ρ(T)$. Our results show that KCo$_2$As$_2$ provides a new avenue for investigating the physics of high-purity metals.

cond-mat.str-el↗

arXiv2022

Handedness-filter and Doppler shift of spin waves in ferrimagnetic domain walls

Excitation and propagation of spin waves inside magnetic domain walls has received attention because of their potentials in spintronic and communication applications. Besides wave amplitude and frequency, spin-wave has its third character: handedness, whose manipulation is certainly of interest. We propose in this Letter that the handedness of low energy spin-wave excitations can be controlled by tuning the net angular momentum δs in a ferrimagnetic (FiM) domain wall, attributing to the inequivalent magnetic sublattices. The results indicate that the spin-wave dispersion depends on both δs and wave handedness. For a positive (negative) δs, a gapless dispersion is observed for the left-handed (righ-handed) spin waves, while a frequency gap appears for the right-handed (left-handed) spin waves. Thus a FiM wall could serve as a multifold filter of low energy spin-wave in which only spin waves with particular handedness can propagate. Furthermore, the energy consumption loss for spin-wave excitation in the wall is much lower than that inside the domain, while the group velocity is much faster too, demonstrating the advantages of domain walls serving as spin waveguides. Moreover, the current-induced spin-wave Doppler shift in the FiM wall is also revealed, and can be controlled by δs. This work unveils for the first time the interesting spin-wave dynamics in FiM domain walls, benefiting future spin-wave applications.

physics.app-ph↗

arXiv2022

A Study on the radon removal performance of low background activated carbon

Radon and radon daughters pose significant backgrounds to rare-event searching experiments. Activated carbon, which has very strong adsorption capacity for radon, can be used for radon removal and radon enrichment. The internal $^{226}$Ra concentration ultimately limits its radon enrichment ability. In order to measure the intrinsic background and study the radon adsorption capability of Saratech activated carbon at various temperatures, a radon-emanation measurement system with a high-sensitivity radon detector and an adsorption-performance research-system have been developed. In this paper, a 0.71~mBq/m$^3$ high-sensitivity radon detector and measurement details of the radon-adsorption capability of Saratech activated carbon at low temperature will be presented.

physics.ins-det↗

arXiv2022

BLEMAB European project: muon imaging technique applied to blast furnaces

The BLEMAB European project (BLast furnace stack density Estimation through online Muon ABsorption measurements), evolution of the previous MuBlast European project, is designed to investigate in detail the capability of muon radiography techniques applied to the imaging of a blast furnace's inner zone. In particular, the geometry and size of the so called cohesive zone, i.e. the spatial zone where the slowly downward moving material begins to soften and melt, that plays an important role in the performance of the blast furnace itself. Thanks to the high penetration power of the natural cosmic ray muon radiation, muon transmission radiography represents an appropriate non-invasive methodology for imaging large high-density structures such as blast furnaces, whose linear size can be up to a few tens of meters. A state-of-the-art muon tracking system, whose design profits from the long experience of our collaboration in this field, is currently under development and will be installed in 2022 at a blast furnace on the ArcelorMittal site in Bremen (Germany) for many months. Collected data will be exploited to monitor temporal variations of the average density distribution inside the furnace. Muon radiography results will also be compared with measurements obtained through an enhanced multipoint probe and standard blast furnace models.

physics.ins-det↗

arXiv2021

Higher-order valley vortices enabled by synchronized rotation in a photonic crystal

Synchronized rotation of unit cells in a periodic structure provides a novel design perspective for manipulation of band topology. We then design a two-dimensional version of higher-order topological insulators (HOTI), by such rotation in a triangular photonic lattice with $\mathcal{C}_3$ symmetry. This HOTI supports the hallmark zero-dimensional corner states and simultaneously the one-dimensional edge states. We also find that our photonic corner states carry chiral orbital angular momenta locked by valleys, whose wavefunctions are featured by the phase vortex (singularity) positioned at the maximal Wyckoff points. Moreover, when excited by a fired source with various frequencies, the valley topological states of both one-dimensional edges and zero-dimensional corners emerge simultaneously. Extendable to higher or synthetic dimensions, our work provides access to a chiral vortex platform for HOTI realisations in the THz photonic system.

physics.optics↗

arXiv2021

Machine Learning Empowered Resource Allocation in IRS Aided MISO-NOMA Networks

A novel framework of intelligent reflecting surface (IRS)-aided multiple-input single-output (MISO) non-orthogonal multiple access (NOMA) network is proposed, where a base station (BS) serves multiple clusters with unfixed number of users in each cluster. The goal is to maximize the sum rate of all users by jointly optimizing the passive beamforming vector at the IRS, decoding order, power allocation coefficient vector and number of clusters, subject to the rate requirements of users. In order to tackle the formulated problem, a three-step approach is proposed. More particularly, a long short-term memory (LSTM) based algorithm is first adopted for predicting the mobility of users. Secondly, a K-means based Gaussian mixture model (K-GMM) algorithm is proposed for user clustering. Thirdly, a deep Q-network (DQN) based algorithm is invoked for jointly determining the phase shift matrix and power allocation policy. Simulation results are provided for demonstrating that the proposed algorithm outperforms the benchmarks, while the throughput gain of 35% can be achieved by invoking NOMA technique instead of orthogonal multiple access (OMA).

eess.SP↗

arXiv2021

A comparative analysis of pulse time-of-arrival creation methods

Extracting precise pulse times of arrival (TOAs) and their uncertainties is the first and most fundamental step in high-precision pulsar timing. In the classical method, TOAs are derived from total intensity pulse profiles of pulsars via cross-correlation with an idealised `1D' template of that profile. While a number of results have been presented in the literature relying on the ever increasing sensitivity of such pulsar timing experiments, there is no consensus on the most reliable methods for TOA creation and, more importantly, the associated TOA uncertainties for each scheme. In this article, we present a comprehensive comparison of TOA determination practices, focusing on the creation of timing templates, TOA determination methods and the most useful TOA bandwidth. The aim is both to present a possible approach towards TOA optimisation as well as the (partial) identification of an optimal TOA-creation scheme and the demonstration of optimisation differences between pulsars and data sets. We compare the values of data-derived template profiles as compared to analytic profiles and evaluate the three most commonly used template-matching methods. Finally, we study the relation between timing precision and TOA bandwidth to identify any potential breaks in that relationship. As a practical demonstration, we apply our selected methods to European Pulsar Timing Array data on the three test pulsars PSRs\ J0218+4232, J1713+0747 and J2145$-$0750.

astro-ph.IM↗