arXiv subjects

Weidong Li

Publications and source records attributed to Weidong Li.

At least 73 records · Page 4Linked to original sources

arXiv2019

Wavelength Dependent Tunneling Delay Time

A clear consensus on how long it takes a particle to tunnel through a potential barrier has never been so urgently required, since the electron dynamics in strong-field ionization can be resolved on attosecond time-scale in experiment and the exact nature of the tunneling process is the key to trigger subsequent attosecond techniques. Here a general picture of tunneling time is suggested by introducing a quantum travel time, which is defined as the ratio of the travel distance to the expected value of the velocity operator under the barrier. Specially, if applied to rectangular barrier tunneling, it can retrieve the Büttiker-Landauer time $τ_{BL}$ in the case of an opaque barrier, and has a clear physical meaning in the case of a very thin barrier wherein $τ_{BL}$ can not be well defined. In the case of strong-field tunneling process, with the help of the newly defined time, the tunneling delay time measured by attoclock experiment can be interpreted as a travel time spent by the electron to tunnel from a point under the barrier to the tunnel exit. In addition, a peculiar oscillation structure in the wavelength dependence of tunneling delay time in deep tunneling regime is observed, which is beyond the scope of adiabatic tunneling picture. This oscillation structure can be attributed to the interference between the ground state tunneling channel and the excited states tunneling channels.

physics.atom-ph↗

arXiv2019

Characterizing the multipartite continuous-variable entanglement structure from squeezing coefficients and the Fisher information

Understanding the distribution of quantum entanglement over many parties is a fundamental challenge of quantum physics and is of practical relevance for several applications in the field of quantum information. Here we use methods from quantum metrology to microscopically characterize the entanglement structure of multimode continuous-variable states in all possible multi-partitions and in all reduced distributions. From experimentally measured covariance matrices of Gaussian states with 2, 3, and 4 photonic modes with controllable losses, we extract the metrological sensitivity as well as an upper separability bound for each partition. An entanglement witness is constructed by comparing the two quantities. Our analysis demonstrates the usefulness of these methods for continuous-variable systems and provides a detailed geometric understanding of the robustness of cluster-state entanglement under photon losses.

quant-ph↗

arXiv2018

A method of detector and event visualization with Unity in JUNO

A visualization method based on Unity engine is proposed for the Jiangmen Underground Neutrino Observatory (JUNO) experiment. The method has been applied in development of a new event display tool named ELAINA (Event Live Animation with unIty for Neutrino Analysis), which provides an intuitive way for users to observe the detector geometry, to tune the reconstruction algorithm and to analyze the physics events. In comparison with the traditional ROOT-based event display, ELAINA provides better visual effects with the Unity engine. It is developed independently of the JUNO offline software but shares the same detector description and event data model in JUNO offline with interfaces. Users can easily download and run the event display on their local computers with different operation systems.

physics.ins-det↗

arXiv2018

Markov chain random fields, spatial Bayesian networks, and optimal neighborhoods for simulation of categorical fields

The Markov chain random field (MCRF) model/theory provides a non-linear spatial Bayesian updating solution at the neighborhood nearest data level for simulating categorical spatial variables. In the MCRF solution, the spatial dependencies among nearest data and the central random variable is a probabilistic directed acyclic graph that conforms to a neighborhood-based Bayesian network on spatial data. By selecting different neighborhood sizes and structures, applying the spatial conditional independence assumption to nearest neighbors, or incorporating ancillary information, one may construct specific MCRF models based on the MCRF general solution for various application purposes. Simplified MCRF models based on assuming the spatial conditional independence of nearest data involve only spatial transition probabilities, and one can implement them easily in sequential simulations. In this article, we prove the spatial Bayesian network characteristic of MCRFs, and test the optimal neighborhoods under the spatial conditional independence assumption. The testing results indicate that the quadrantal (i.e., one nearest datum per quadrant) neighborhood is generally the best choice for the simplified MCRF solution, performing better than other sectored neighborhoods and non-sectored neighborhoods with regard to simulation accuracy and pattern rationality.

stat.ME↗

arXiv2018

The Berkeley Sample of Stripped-Envelope Supernovae

We present the complete sample of stripped-envelope supernova (SN) spectra observed by the Lick Observatory Supernova Search (LOSS) collaboration over the last three decades: 888 spectra of 302 SNe, 652 published here for the first time, with 384 spectra (of 92 SNe) having photometrically-determined phases. After correcting for redshift and Milky Way dust reddening and reevaluating the spectroscopic classifications for each SN, we construct mean spectra of the three major spectral subtypes (Types IIb, Ib, and Ic) binned by phase. We compare measures of line strengths and widths made from this sample to the results of previous efforts, confirming that O I λ7774 absorption is stronger and found at higher velocity in Type Ic SNe than in Types Ib or IIb SNe in the first 30 days after peak brightness, though the widths of nebular emission lines are consistent across subtypes. We also highlight newly available observations for a few rare subpopulations of interest.

astro-ph.SR↗

arXiv2018

The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad-Line Region

We present models of the H$β$-emitting broad-line region (BLR) in seven Seyfert 1 galaxies from the Lick AGN (Active Galactic Nucleus) Monitoring Project 2011 sample, drawing inferences on the BLR structure and dynamics as well as the mass of the central supermassive black hole. We find that the BLR is generally a thick disk, viewed close to face-on, with preferential emission back toward the ionizing source. The dynamics in our sample range from near-circular elliptical orbits to inflowing or outflowing trajectories. We measure black hole masses of $\log_{10}(M_{\rm BH}/M_\odot) = 6.48^{+0.21}_{-0.18}$ for PG 1310$-$108, $7.50^{+0.25}_{-0.18}$ for Mrk 50, $7.46^{+0.15}_{-0.21}$ for Mrk 141, $7.58^{+0.08}_{-0.08}$ for Mrk 279, $7.11^{+0.20}_{-0.17}$ for Mrk 1511, $6.65^{+0.27}_{-0.15}$ for NGC 4593, and $6.94^{+0.14}_{-0.14}$ for Zw 229$-$015. We use these black hole mass measurements along with cross-correlation time lags and line widths to recover the scale factor $f$ used in traditional reverberation mapping measurements. Combining our results with other studies that use this modeling technique, bringing our sample size to 16, we calculate a scale factor that can be used for measuring black hole masses in other reverberation mapping campaigns. When using the root-mean-square (rms) spectrum and using the line dispersion to measure the line width, we find $\log_{10}(f_{{\rm rms},σ})_{\rm pred} = 0.57 \pm 0.19$. Finally, we search for correlations between $f$ and other AGN and BLR parameters and find marginal evidence that $f$ is correlated with $M_{\rm BH}$ and the BLR inclination angle, but no significant evidence of a correlation with the AGN luminosity or Eddington ratio.

astro-ph.GA↗

arXiv2018

A vertex reconstruction algorithm in the central detector of JUNO

The Jiangmen Underground Neutrino Observatory (JUNO) is designed to study neutrino mass hierarchy and measure three of the neutrino oscillation parameters with high precision using reactor antineutrinos. It is also able to study many other physical phenomena, including supernova neutrinos, solar neutrinos, geo-neutrinos, atmosphere neutrinos, and so forth. The central detector of JUNO contains 20,000~tons of liquid scintillator (LS) and about 18,000 20-inch photomultiplier tubes (PMTs), which is the largest liquid scintillator one under construction in the world up today. The energy resolution is expected to be 3\%/$\sqrt{E(MeV)}$. To meet the requirements of the experiment, an algorithm of vertex reconstruction, which takes into account time and charge information of PMTs, has been developed by deploying the maximum likelihood method and well understanding the complicated optical processes in the liquid scintillator.

physics.ins-det↗

arXiv2018

Frequentist and Bayesian Quantum Phase Estimation

Frequentist and Bayesian phase estimation strategies lead to conceptually different results on the state of knowledge about the true value of the phase shift. We compare the two frameworks and their sensitivity bounds to the estimation of an interferometric phase shift limited by quantum noise, considering both the cases of a fixed and a fluctuating parameter. We point out that frequentist precision bounds, such as the Cramèr-Rao bound, for instance, do not apply to Bayesian strategies and vice-versa. Similarly, bounds for fluctuating parameters make no statement about the estimation of a fixed parameter.

quant-ph↗

arXiv2018

Muon Tracking with the fastest light in the JUNO Central Detector

The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment designed to measure the neutrino mass hierarchy using a central detector (CD), which contains 20 kton liquid scintillator (LS) surrounded by about 18,000 photomultiplier tubes (PMTs), located 700~m underground. The rate of cosmic muons reaching the JUNO detector is about 3~Hz and the muon induced neutrons and isotopes are major backgrounds for the neutrino detection. Reconstruction of the muon trajectory in the detector is crucial for the study and rejection of those backgrounds. This paper will introduce the muon tracking algorithm in the JUNO CD, with a least squares method of PMTs' first hit time (FHT). Correction of the FHT for each PMT was found to be important to reduce the reconstruction bias. The spatial resolution and angular resolution are better than 3~cm and 0.4~degree, respectively, and the tracking efficiency is greater than 90\% up to 16~m far from the detector center.

physics.ins-det↗

arXiv2018

Hyper- and hybrid nonlocality

The controlled generation and identification of quantum correlations, usually encoded in either qubits or continuous degrees of freedom, builds the foundation of quantum information science. Recently, more sophisticated approaches, involving a combination of two distinct degrees of freedom have been proposed to improve on the traditional strategies. Hyperentanglement describes simultaneous entanglement in more than one distinct degree of freedom, whereas hybrid entanglement refers to entanglement shared between a discrete and a continuous degree of freedom. In this work we propose a scheme that allows to combine the two approaches, and to extend them to the strongest form of quantum correlations. Specifically, we show how two identical, initially separated particles can be manipulated to produce Bell nonlocality among their spins, among their momenta, as well as across their spins and momenta. We discuss possible experimental realizations with atomic and photonic systems.

quant-ph↗

arXiv2018

A ROOT Based Event Display Software for JUNO

An event display software SERENA has been designed for the Jiangmen Underground Neutrino Observatory (JUNO). The software has been developed in the JUNO offline software system and is based on the ROOT display package EVE. It provides an essential tool to display detector and event data for better understanding of the processes in the detectors. The software has been widely used in JUNO detector optimization, simulation, reconstruction and physics study.

physics.ins-det↗

arXiv2017

The Carnegie Supernova Project I: Third Photometry Data Release of Low-Redshift Type Ia Supernovae and Other White Dwarf Explosions

We present final natural system optical (ugriBV) and near-infrared (YJH) photometry of 134 supernovae (SNe) with probable white dwarf progenitors that were observed in 2004-2009 as part of the first stage of the Carnegie Supernova Project (CSP-I). The sample consists of 123 Type Ia SNe, 5 Type Iax SNe, 2 super-Chandrasekhar SN candidates, 2 Type Ia SNe interacting with circumstellar matter, and 2 SN 2006bt-like events. The redshifts of the objects range from z = 0.0037 to 0.0835; the median redshift is 0.0241. For 120 (90%) of these SNe, near-infrared photometry was obtained. Average optical extinction coefficients and color terms are derived and demonstrated to be stable during the five CSP-I observing campaigns. Measurements of the CSP-I near-infrared bandpasses are also described, and near-infrared color terms are estimated through synthetic photometry of stellar atmosphere models. Optical and near-infrared magnitudes of local sequences of tertiary standard stars for each supernova are given, and a new calibration of Y-band magnitudes of the Persson et al. (1998) standards in the CSP-I natural system is presented.

astro-ph.IM↗

arXiv2017

Parallelized JUNO simulation software based on SNiPER

The Jiangmen Underground Neutrino Observatory (JUNO) is a neutrino experiment to determine neutrino mass hierarchy. It has a central detector used for neutrino detection, which consists of a spherical acrylic vessel containing 20 kt LS and about 18,000 20-inch PMTs to collect light from LS. Around the CD, there is a water pool to shield radioactivities. The WP is equipped with about 2000 PMTs to measure cosmic ray muons by detecting Cherenkov light. As one of the important parts in JUNO offline software, the serial simulation framework is developed based on SNiPER. It is in charge of physics generator, detector simulation, event mixing and digitization. However Geant4 based detector simulation of such a large detector is time-consuming and challenging. It is necessary to take full advantages of parallel computing to speedup simulation. Starting from version 10, Geant4 supports event-level parallelism. Even though based on pthread, it could be extended with other libraries such as Intel TBB. Therefore it is possible to parallelize JUNO simulation framework via integrating Geant4 and SNiPER. In this paper, our progress in developing parallelized simulation software are presented. The SNiPER framework can run in sequential mode, Intel TBB mode or other modes. The SNiPER task component is in charge of event loop, which is like a simplified application manager. Two types of tasks are introduced in the simulation framework, one is global task and another is worker task. The global task will run only once to initialize detector geometry and physics processes. The worker tasks will be spawned after global task is done. In each worker task, a Geant4 run manager is invoked to do the real simulation. Therefore the simulation framework and the underlying TBB have been decoupled. Finally, the software performance of parallelized JUNO simulation software is also presented.

physics.ins-det↗

arXiv2017

LOSS Revisited - II: The relative rates of different types of supernovae vary between low- and high-mass galaxies

In Paper I of this series, we showed that the ratio between stripped-envelope (SE) supernova (SN) and Type II SN rates reveals a significant SE SN deficiency in galaxies with stellar masses $\lesssim 10^{10}~{\rm M}_\odot$. Here, we test this result by splitting the volume-limited subsample of the Lick Observatory Supernova Search (LOSS) SN sample into low- and high-mass galaxies and comparing the relative rates of various SN types found in them. The LOSS volume-limited sample contains 180 SNe and SN impostors and is complete for SNe Ia out to 80 Mpc and core-collapse SNe out to 60 Mpc. All of these transients were recently reclassified by us in Shivvers et al. (2017). We find that the relative rates of some types of SNe differ between low- and high-mass galaxies: SNe Ib and Ic are underrepresented by a factor of ~3 in low-mass galaxies. These galaxies also contain the only examples of SN 1987A-like SNe in the sample and host about 9 times as many SN impostors. Normal SNe Ia seem to be ~30\% more common in low-mass galaxies, making these galaxies better sources for homogeneous SN Ia cosmology samples. The relative rates of SNe IIb are consistent in both low- and high-mass galaxies. The same is true for broad-line SNe Ic, although our sample includes only two such objects. The results presented here are in tension with a similar analysis from the Palomar Transient Factory, especially as regards SNe IIb.

astro-ph.HE↗

arXiv2017

LOSS Revisited - I: Unraveling correlations between supernova rates and galaxy properties, as measured in a reanalysis of the Lick Observatory Supernova Search

Most types of supernovae (SNe) have yet to be connected with their progenitor stellar systems. Here, we reanalyze the 10-year SN sample collected during 1998-2008 by the Lick Observatory Supernova Search (LOSS) in order to constrain the progenitors of SNe Ia and stripped-envelope SNe (SE SNe, i.e., SNe~IIb, Ib, Ic, and broad-lined Ic). We matched the LOSS galaxy sample with spectroscopy from the Sloan Digital Sky Survey and measured SN rates as a function of galaxy stellar mass, specific star formation rate, and oxygen abundance (metallicity). We find significant correlations between the SN rates and all three galaxy properties. The SN Ia correlations are consistent with other measurements, as well as with our previous explanation of these measurements in the form of a combination of the SN Ia delay-time distribution and the correlation between galaxy mass and age. The ratio between the SE SN and SN II rates declines significantly in low-mass galaxies. This rules out single stars as SE~SN progenitors, and is consistent with predictions from binary-system progenitor models. Using well-known galaxy scaling relations, any correlation between the rates and one of the galaxy properties examined here can be expressed as a correlation with the other two. These redundant correlations preclude us from establishing causality - that is, from ascertaining which of the galaxy properties (or their combination) is the physical driver for the difference between the SE SN and SN II rates. We outline several methods that have the potential to overcome this problem in future works.

astro-ph.HE↗

arXiv2017

The Application of SNiPER to the JUNO Simulation

JUNO is a multipurpose neutrino experiment which is designed to determine neutrino mass hierarchy and precisely measure oscillation parameters. As one of the important systems, the JUNO offline software is being developed using the SNiPER software. In this proceeding, we focus on the requirements of JUNO simulation and present the working solution based on the SNiPER. The JUNO simulation framework is in charge of managing event data, detector geometries and materials, physics processes, simulation truth information etc. It glues physics generator, detector simulation and electronics simulation modules together to achieve a full simulation chain. In the implementation of the framework, many attractive characteristics of the SNiPER have been used, such as dynamic loading, flexible flow control, multiple event management and Python binding. Furthermore, additional efforts have been made to make both detector and electronics simulation flexible enough to accommodate and optimize different detector designs. For the Geant4-based detector simulation, each sub-detector component is implemented as a SNiPER tool which is a dynamically loadable and configurable plugin. So it is possible to select the detector configuration at runtime. The framework provides the event loop to drive the detector simulation and interacts with the Geant4 which is implemented as a passive service. All levels of user actions are wrapped into different customizable tools, so that user functions can be easily extended by just adding new tools. The electronics simulation has been implemented by following an event driven scheme. The SNiPER task component is used to simulate data processing steps in the electronics modules. The electronics and trigger are synchronized by triggered events containing possible physics signals.

physics.ins-det↗

arXiv2016

Study of BESIII electromagnetic calorimeter performance with radiative lepton pair events

We study the photon detection efficiency and position resolution of the electromagnetic calorimeter (EMC) of the BESIII detector. The control samples of the initial-state-radiation (ISR) process of $e^+e^-\rightarrow γμ^+μ^-$ at $J/ψ$ and $ψ(3770)$ resonances are used for the calibration of the photon cluster shapes and photon detection efficiency study. The photon detection efficiency is defined as the fraction of predicted photon, determined by performing a kinematic fit with the four momenta of two charged tracks only, matched with the actual photons in the EMC. The spatial resolution of the EMC is studied in polar ($θ$) and azimuthal ($ϕ$) angle directions in a cylindrical coordinate system centered at the interaction point, with z-axis along the beam direction.

hep-ex↗

arXiv2016

Multi-resource Fair Allocation with Bounded Number of Tasks in Cloud Computing Systems

Dominant resource fairness (DRF) is a popular mechanism for multi-resource allocation in cloud computing systems. In this paper, we consider a problem of multi-resource fair allocation with bounded number of tasks. Firstly, we propose the lexicographically max-min normalized share (LMMNS) fair allocation mechanism, which is a natural generalization of DRF, and design a non-trivial optimal algorithm to find a LMMNS fair allocation, whose running time is linear in the number of users. Secondly, we prove that LMMNS satisfies envy-freeness (EF) and group strategy-proofness (GSP), and analysis the approximation ratios of LMMNS, by exploiting the properties of the optimal solution. Thirdly, we propose a modified version of LMMNS, which is the second mechanism satisfying sharing incentive, EF, and GSP. Finally, we have implemented LMMNS, and show that it has a good average-case performance, especially when the number of resources is 2.

cs.GT↗