arXiv subjects

X. Huang

Publications and source records attributed to X. Huang.

At least 91 records · Page 5Linked to original sources

arXiv2021

Discovering New Strong Gravitational Lenses in the DESI Legacy Imaging Surveys

We have conducted a search for new strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys' Data Release 8. We use deep residual neural networks, building on previous work presented in Huang et al. (2020). These surveys together cover approximately one third of the sky visible from the northern hemisphere, reaching a z band AB magnitude of ~22.5. We compile a training sample that consists of known lensing systems as well as non-lenses in the Legacy Surveys and the Dark Energy Survey. After applying our trained neural networks to the survey data, we visually inspect and rank images with probabilities above a threshold. Here we present 1210 new strong lens candidates.

astro-ph.IM↗

arXiv2020

Discriminative Feature Representation with Spatio-temporal Cues for Vehicle Re-identification

Vehicle re-identification (re-ID) aims to discover and match the target vehicles from a gallery image set taken by different cameras on a wide range of road networks. It is crucial for lots of applications such as security surveillance and traffic management. The remarkably similar appearances of distinct vehicles and the significant changes of viewpoints and illumination conditions take grand challenges to vehicle re-ID. Conventional solutions focus on designing global visual appearances without sufficient consideration of vehicles' spatiotamporal relationships in different images. In this paper, we propose a novel discriminative feature representation with spatiotemporal clues (DFR-ST) for vehicle re-ID. It is capable of building robust features in the embedding space by involving appearance and spatio-temporal information. Based on this multi-modal information, the proposed DFR-ST constructs an appearance model for a multi-grained visual representation by a two-stream architecture and a spatio-temporal metric to provide complementary information. Experimental results on two public datasets demonstrate DFR-ST outperforms the state-of-the-art methods, which validate the effectiveness of the proposed method.

cs.CV↗

arXiv2020

Measurement of the mass difference and the binding energy of the hypertriton and antihypertriton

According to the CPT theorem, which states that the combined operation of charge conjugation, parity transformation and time reversal must be conserved, particles and their antiparticles should have the same mass and lifetime but opposite charge and magnetic moment. Here, we test CPT symmetry in a nucleus containing a strange quark, more specifically in the hypertriton. This hypernucleus is the lightest one yet discovered and consists of a proton, a neutron, and a $Λ$ hyperon. With data recorded by the STAR detector{\cite{TPC,HFT,TOF}} at the Relativistic Heavy Ion Collider, we measure the $Λ$ hyperon binding energy $B_Λ$ for the hypertriton, and find that it differs from the widely used value{\cite{B_1973}} and from predictions{\cite{2019_weak, 1995_weak, 2002_weak, 2014_weak}}, where the hypertriton is treated as a weakly bound system. Our results place stringent constraints on the hyperon-nucleon interaction{\cite{Hammer2002, STAR-antiH3L}}, and have implications for understanding neutron star interiors, where strange matter may be present{\cite{Chatterjee2016}}. A precise comparison of the masses of the hypertriton and the antihypertriton allows us to test CPT symmetry in a nucleus with strangeness for the first time, and we observe no deviation from the expected exact symmetry.

hep-ex↗

arXiv2020

A novel quad-channel 10 Gbps CMOS VCSEL array driver with integrated charge pumps

We present a novel design and the test results of a 4-channel driver for an array of Vertical-Cavity Surface-Emitting Lasers (VCSELs). This ASIC, named cpVLAD and fabricated in a 65 nm CMOS technology, has on-chip charge pumps and is for data rates up to 10 Gbps per channel. The charge pumps are implemented to address the issue of voltage margin of the VCSEL driving stage in the applications under low temperature and harsh radiation environment. Test results indicate that cpVLAD is capable of driving VCSELs with forward voltages of up to 2.8 V using 1.2 V and 2.5 V power supplies with a power consumption of 94 mW/channel.

physics.ins-det↗

arXiv2020

Inverse problems for a half-order time-fractional diffusion equation in arbitrary dimension by Carleman estimates

We consider a half-order time-fractional diffusion equation in an arbitrary dimension and investigate inverse problems of determining the source term or the diffusion coefficient from spatial data at an arbitrarily fixed time under some additional assumptions. We establish the stability estimate of Lipschitz type in the inverse problems and the proofs are based on the Bukhgeim-Klibanov method by using Carleman estimates.

math.AP↗

arXiv2020

Optical transceivers for event triggers in the ATLAS phase-I upgrade

The ATLAS phase-I upgrade aims to enhance event trigger performance in the Liquid Argon (LAr) calorimeter and the forward muon spectrometer. The trigger signals are transmitted by optical transceivers at 5.12 Gbps per channel in a radiation field. We report the design, quality control in production and ageing test of the transceivers fabricated with the LOCld laser driver and multi-mode 850 nm vertical-cavity surface-emitting laser (VCSEL). The modules are packaged in miniature formats of dual-channel transmitter (MTx) and transceiver (MTRx) for the LAr. The transmitters are also packaged in small form-factor pluggable (SFP) for the muon spectrometer. In production, the LOCld chips and VCSELs in TOSA package were examined before assembly. All of the modules were tested and selected during production for quality control based on the eye-diagram parameters measured at 5.12 Gbps. The yield is 98 % for both the MTx and MTRx on a total 4.7k modules. The uniformity of transmitter channels of a MTx was assured by choosing the TOSA components with approximately equal light powers. The ageing effect is monitored in burn-in of a small batch of transmitter modules with bit-error test and eye-diagrams measured periodically. The observables are stable with the light power degradation within 5 % over a period of more than 6k hours.

physics.ins-det↗

arXiv2020

Signature of Unconventional Superconductivity in a Copper-based Metal-Organic Framework with Perfect Kagome Structure

Recently, the superconductivity in a metal-organic framework (MOF) has been discovered for the first time in copper(II) benzenehexathiolate ([Cu$_3$(C$_6$S$_6$)]$_n$, Cu-BHT). The Cu atoms form a two-dimensional perfect Kagome lattice, which has the potential to host a metallic quantum spin liquid state. Here we present high-precision measurements of in-plane magnetic penetration depth $λ$ in Cu-BHT films down to 40\,mK. The temperature dependence of $λ$ shows a non-exponential, quasi-linear behavior at low temperatures, suggesting that unconventional superconductivity with low-energy quasiparticle excitations is realized in this system. With the reported non-Fermi liquid behavior, this finding implies that MOFs can provide a flexible platform to investigate the superconducting pairing mechanisms in the presence of spin frustration and strong quantum fluctuations.

cond-mat.supr-con↗

arXiv2020

A 4-Channel 10-Gbps/ch CMOS VCSEL Array Driver with on-chip Charge-pumps

We present the design and test results of a 4-channel 10-Gbps/ch Vertical-Cavity Surface-Emitting Laser array driver, the cpVLAD. With on-chip charge-pumps to extend the biasing headroom for the VCSELs needed for low temperature operation and mitigation of the radiation effects. The cpVLAD was fabricated in a 65-nm CMOS technology. The test results show that the cpVLAD is capable of driving VCSELs with forward bias voltages as high as 2.8 V from a 2.5 V power supply. The power consumption of the cpVLAD is 94 mW/ch.

physics.ins-det↗

arXiv2020

Physics-informed Gaussian Process for Online Optimization of Particle Accelerators

High-dimensional optimization is a critical challenge for operating large-scale scientific facilities. We apply a physics-informed Gaussian process (GP) optimizer to tune a complex system by conducting efficient global search. Typical GP models learn from past observations to make predictions, but this reduces their applicability to new systems where archive data is not available. Instead, here we use a fast approximate model from physics simulations to design the GP model. The GP is then employed to make inferences from sequential online observations in order to optimize the system. Simulation and experimental studies were carried out to demonstrate the method for online control of a storage ring. We show that the physics-informed GP outperforms current routinely used online optimizers in terms of convergence speed, and robustness on this task. The ability to inform the machine-learning model with physics may have wide applications in science.

physics.comp-ph↗

arXiv2020

First measurement of $Λ_c$ baryon production in Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV

We report on the first measurement of the charmed baryon $Λ_c^{\pm}$ production at midrapidity ($|y|$ $<$ 1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The $Λ_c$/$D^0$ (denoting ($Λ_c^++Λ_c^-$)/($D^0+\bar{D^0}$)) yield ratio is measured to be 1.08 $\pm$ 0.16 (stat.) $\pm$ 0.26 (sys.) in the 0--20% most central Au+Au collisions for the transverse momentum ($p_T$) range 3 $<$ $p_T$ $<$ 6 GeV/$c$. This is significantly larger than the PYTHIA model calculations for $p+p$ collisions. The measured $Λ_c$/$D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured $Λ_c$/$D^0$ ratio.

nucl-ex↗

arXiv2020

Characterization of a gigabit transceiver for the ATLAS inner tracker pixel detector readout upgrade

We present a gigabit transceiver prototype Application Specific Integrated Circuit (ASIC), GBCR, for the ATLAS Inner Tracker (ITk) Pixel detector readout upgrade. GBCR is designed in a 65-nm CMOS technology and consists of four upstream receiver channels, a downstream transmitter channel, and an Inter-Integrated Circuit (I2C) slave. The upstream channels receive the data at 5.12 Gbps passing through 5-meter 34-American Wire Gauge (AWG) Twin-axial (Twinax) cables, equalize them, retime them with a recovered clock, and then drive an optical transmitter. The downstream channel receives the data at 2.56 Gbps from an optical receiver and drives the cable as same as the upstream channels. The jitter of the upstream channel output is measured to be 35 ps (peak-peak) when the Clock-Data Recovery (CDR) module is turned on and the jitter of the downstream channel output after the cable is 138 ps (peak-peak). The power consumption of each upstream channel is 72 mW when the CDR module is turned on and the downstream channel consumes 27 mW. GBCR survives the total ionizing dose of 200 kGy.

physics.ins-det↗

arXiv2020

Design and hardware evaluation of the optical-link system for the ATLAS Liquid Argon Calorimeter Phase-II Upgrade

An optical link system is being developed for the ATLAS Liquid Argon Calorimeter Phase-II upgrade. The optical link system is responsible for transmit the data of over 182 thousand detector channels from 1524 Front-End Boards (FEBs) through 26 optical fibers per FEB over 150 meters to the counting room and brings clocks, bunch crossing reset signals and slow control/monitoring signals back to the FEBs. The optical link system is based on the Low-Power GigaBit Transceivers (lpGBTs) and the Versatile optical Transceiver (VTRx+) modules, which both are being developed for the High-Luminosity LHC upgrade. An evaluation board is designed and the major functions of the optical link system are being evaluated. The design of the optical link system and the evaluation of major functions are presented in the paper.

physics.ins-det↗

arXiv2020

Prototyping of a 25 Gbps optical transmitter for applications in high-energy physics experiments

Development of optical links with 850 nm multi-mode vertical-cavity surface-emitting lasers (VCSELs) has advanced to 25 Gbps in speed. For applications in high-energy experiments, the transceivers are required to be tolerant in radiation and particle fields. We report on prototyping of a miniature transmitter named MTx+, which is developed for high speed transmission with the dual-channel laser driver LOCld65 and 850 nm VCSELs packaged in TOSA format. The LOCld65 is fabricated in the TSMC 65 nm process and is packaged in the QFN-40 for assembly. The MTx+ modules and test kits were first made with PCB and components qualified for 10 Gbps applications, and were tested for achieving 14 Gbps. The data transfer rate of the MTx+ module is investigated further for the speed of up to 25 Gbps. The LOCld65 is examined with post-layout simulation and the module design upgraded with components including the TOSA qualified for 25 Gbps applications. The PCB material is replaced by the Panasonic MEGTRON6. The revised MTx+ is tested at 25 Gbps and the eye-diagram shows a mask margin of 22 %.

physics.ins-det↗

arXiv2020

The Compact Triply Eclipsing Triple Star TIC 209409435 Discovered with TESS

We report the discovery in $TESS$ Sectors 3 and 4 of a compact triply eclipsing triple star system. TIC 209409435 is a previously unknown eclipsing binary with a period of 5.717 days, and the presence of a third star in an outer eccentric orbit of 121.872 day period was found from two sets of third-body eclipses and from eclipse timing variations. The latter exhibit signatures of strong 3rd-body perturbations. After the discovery, we obtained follow-up ground-based photometric observations of several binary eclipses as well as another of the third-body eclipses. We carried out comprehensive analyses, including the simultaneous photodynamical modelling of $TESS$ and ground-based lightcurves (including both archival WASP data, and our own follow-up measurements), as well as eclipse timing variation curves. Also, we have included in the simultaneous fits multiple star spectral energy distribution data and theoretical PARSEC stellar isochrones. We find that the inner binary consists of near twin stars of mass 0.90 $M_\odot$ and radius 0.88 $R_\odot$. The third star is just 9% more massive and 18% larger in radius. The inner binary has a rather small eccentricity while the outer orbit has $e = 0.40$. The inner binary and outer orbit have inclination angles within 0.1$^\circ$ and 0.2$^\circ$ of 90$^\circ$, respectively. The mutual inclination angle is $\lesssim 1/4^\circ$. All of these results were obtained without radial velocity observations.

astro-ph.SR↗

arXiv2019

Stability for inverse source problems by Carleman estimates

In this article, we provide a modified argument for proving conditional stability for inverse problems of determining spatially varying functions in evolution equations by Carleman estimates. Our method needs not any cut-off procedures and can simplify the existing proofs. We establish the conditional stability for inverse source problems for a hyperbolic equation and a parabolic equation, and our method is widely applicable to various evolution equations.

math.AP↗

arXiv2019

Online tuning and light source control using a physics-informed Gaussian process Adi

Operating large-scale scientific facilities often requires fast tuning and robust control in a high dimensional space. In this paper we introduce a new physics-informed optimization algorithm based on Gaussian process regression. Our method takes advantage of the existing domain knowledge in the form of realizations of a physics model of the observed system. We have applied a physics-informed Gaussian Process method experimentally at the SPEAR3 storage ring to demonstrate online accelerator optimization. This method outperforms Gaussian Process trained on data as well as the standard approach routinely used for operation, in terms of convergence speed and optimal point. The proposed method could be applicable to automatic tuning and control of other complex systems, without a prerequisite for any observed data.

physics.acc-ph↗

arXiv2019

Methods for a blind analysis of isobar data collected by the STAR collaboration

In 2018, the STAR collaboration collected data from $_{44}^{96}Ru+_{44}^{96}Ru$ and $_{40}^{96}Zr+_{40}^{96}Zr$ at $\sqrt{s_{NN}}=200$ GeV to search for the presence of the chiral magnetic effect in collisions of nuclei. The isobar collision species alternated frequently between $_{44}^{96}Ru+_{44}^{96}Ru$ and $_{40}^{96}Zr+_{40}^{96}Zr$. In order to conduct blind analyses of studies related to the chiral magnetic effect in these isobar data, STAR developed a three-step blind analysis procedure. Analysts are initially provided a "reference sample" of data, comprised of a mix of events from the two species, the order of which respects time-dependent changes in run conditions. After tuning analysis codes and performing time-dependent quality assurance on the reference sample, analysts are provided a species-blind sample suitable for calculating efficiencies and corrections for individual $\approx30$-minute data-taking runs. For this sample, species-specific information is disguised, but individual output files contain data from a single isobar species. Only run-by-run corrections and code alteration subsequent to these corrections are allowed at this stage. Following these modifications, the "frozen" code is passed over the fully un-blind data, completing the blind analysis. As a check of the feasibility of the blind analysis procedure, analysts completed a "mock data challenge," analyzing data from $Au+Au$ collisions at $\sqrt{s_{NN}}=27$ GeV, collected in 2018. The $Au+Au$ data were prepared in the same manner intended for the isobar blind data. The details of the blind analysis procedure and results from the mock data challenge are presented.

nucl-ex↗

arXiv2019

Beam-energy dependence of identified two-particle angular correlations in Au+Au collisions at RHIC

The two-particle angular correlation functions, $R_2$, of pions, kaons, and protons in Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, and 200 GeV were measured by the STAR experiment at RHIC. These correlations were measured for both like-sign and unlike-sign charge combinations and versus the centrality. The correlations of pions and kaons show the expected near-side ({\it i.e.}, at small relative angles) peak resulting from short-range mechanisms. The amplitudes of these short-range correlations decrease with increasing beam energy. However, the proton correlation functions exhibit strong anticorrelations in the near-side region. This behavior is observed for the first time in an A+A collision system. The observed anticorrelation is $p_{T}$-independent and decreases with increasing beam energy and centrality. The experimental results are also compared to the Monte Carlo models UrQMD, Hijing, and AMPT.

nucl-ex↗