arXiv subjects

Yi Zheng

Publications and source records attributed to Yi Zheng.

At least 145 records · Page 8Linked to original sources

arXiv2021

A Game-Theoretic Taxonomy of Visual Concepts in DNNs

In this paper, we rethink how a DNN encodes visual concepts of different complexities from a new perspective, i.e. the game-theoretic multi-order interactions between pixels in an image. Beyond the categorical taxonomy of objects and the cognitive taxonomy of textures and shapes, we provide a new taxonomy of visual concepts, which helps us interpret the encoding of shapes and textures, in terms of concept complexities. In this way, based on multi-order interactions, we find three distinctive signal-processing behaviors of DNNs encoding textures. Besides, we also discover the flexibility for a DNN to encode shapes is lower than the flexibility of encoding textures. Furthermore, we analyze how DNNs encode outlier samples, and explore the impacts of network architectures on interactions. Additionally, we clarify the crucial role of the multi-order interactions in real-world applications. The code will be released when the paper is accepted.

cs.LG↗

arXiv2021

Flatland Competition 2020: MAPF and MARL for Efficient Train Coordination on a Grid World

The Flatland competition aimed at finding novel approaches to solve the vehicle re-scheduling problem (VRSP). The VRSP is concerned with scheduling trips in traffic networks and the re-scheduling of vehicles when disruptions occur, for example the breakdown of a vehicle. While solving the VRSP in various settings has been an active area in operations research (OR) for decades, the ever-growing complexity of modern railway networks makes dynamic real-time scheduling of traffic virtually impossible. Recently, multi-agent reinforcement learning (MARL) has successfully tackled challenging tasks where many agents need to be coordinated, such as multiplayer video games. However, the coordination of hundreds of agents in a real-life setting like a railway network remains challenging and the Flatland environment used for the competition models these real-world properties in a simplified manner. Submissions had to bring as many trains (agents) to their target stations in as little time as possible. While the best submissions were in the OR category, participants found many promising MARL approaches. Using both centralized and decentralized learning based approaches, top submissions used graph representations of the environment to construct tree-based observations. Further, different coordination mechanisms were implemented, such as communication and prioritization between agents. This paper presents the competition setup, four outstanding solutions to the competition, and a cross-comparison between them.

cs.AI↗

arXiv2021

Expansion series of the pairwise velocity generating function and its implications on redshift space distortion modeling

The pairwise velocity generating function $G$ has deep connection with both the pairwise velocity probability distribution function and modeling of redshift space distortion (RSD). Its implementation into RSD modeling is often faciliated by expansion into series of pairwise velocity moments $\langle v_{12}^n\rangle$. Motivated by the logrithmic transformation of the cosmic density field, we investigate an alternative expansion into series of pairwise velocity cumulants $\langle v_{12}^n\rangle_c$ . We numerically evaluate the convergence rate of the two expansions, with three $3072^3$ particle simulations of the CosmicGrowth N-body simulation series. (1) We find that the cumulant expansion performs significantly better, for all the halo samples and redshifts investigated. (2) For modeling RSD at $k_{\|}<0.1 h$ Mpc$^{-1}$, including only the $n=1,2$ cumulants is sufficient. (3) But for modeling RSD at $k_\parallel=0.2 h$ Mpc$^{-1}$, we need and only need the $n=1,2,3,4$ cumulants. These results provide specific requirements on RSD modeling in terms of $m$-th order statistics of the large scale strucure.

astro-ph.CO↗

arXiv2021

Electron-plasmon interaction induced plasmonic-polaron band replication in epitaxial perovskite SrIrO$_3$ films

Electron-boson interaction is fundamental to a thorough understanding of various exotic properties emerging in many-body physics. In photoemission spectroscopy, photoelectron emission due to photon absorption would trigger diverse collective excitations in solids, including the emergence of phonons, magnons, electron-hole pairs, and plasmons, which naturally provides a reliable pathway to study electron-boson couplings. While fingerprints of electron-phonon/-magnon interactions in this state-of-the-art technique have been well investigated, much less is known about electron-plasmon coupling, and direct observation of the band renormalization solely due to electron-plasmon interactions is extremely challenging. Here by utilizing integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy, we discover the long sought-after pure electron-plasmon coupling-induced low-lying plasmonic-polaron replica bands in epitaxial semimetallic SrIrO$_3$ films, in which the characteristic low carrier concentration and narrow bandwidth combine to provide a unique platform where the electron-plasmon interaction can be investigated kinematically in photoemission spectroscopy. This finding enriches the forms of electron band normalization on collective modes in solids and demonstrates that, to obtain a complete understanding of the quasiparticle dynamics in 5d electron systems, the electron-plasmon interaction should be considered on equal footing with the acknowledged electron-electron interaction and spin-orbit coupling.

cond-mat.str-el↗

arXiv2021

Toward a more stringent test of gravity with redshift space power spectrum: simultaneous probe of growth and amplitude of large-scale structure

Redshift-space distortions (RSD) offers an exciting opportunity to test the gravity on cosmological scales. In the presence of galaxy bias, however, the RSD measurement at large scales, where the linear theory prediction is safely applied, is known to exhibit a degeneracy between the parameters of structure growth f and fluctuation amplitude sigma8, and one can only constrain the parameters in the form of fsigma8. In order to disentangle this degeneracy, in this paper, we go beyond the linear theory, and consider the model of RSD applicable to a weakly nonlinear regime. Based on the Fisher matrix analysis, we show explicitly that the degeneracy of the parameter fsigma8 can be broken, and sigma8 is separately estimated in the presence of galaxy bias. Performing further the Markov chain Monte Carlo analysis, we verify that our model correctly reproduces the fiducial values of fsigma8 and sigma8, with the statistical errors consistent with those estimated from the Fisher matrix analysis. We show that upcoming galaxy survey of the stage-IV class can unambiguously determine sigma8 at the precision down to 10% at higher redshifts even if we restrict the accessible scales to k<0.16h/Mpc

astro-ph.CO↗

arXiv2021

Inheritance-guided Hierarchical Assignment for Clinical Automatic Diagnosis

Clinical diagnosis, which aims to assign diagnosis codes for a patient based on the clinical note, plays an essential role in clinical decision-making. Considering that manual diagnosis could be error-prone and time-consuming, many intelligent approaches based on clinical text mining have been proposed to perform automatic diagnosis. However, these methods may not achieve satisfactory results due to the following challenges. First, most of the diagnosis codes are rare, and the distribution is extremely unbalanced. Second, existing methods are challenging to capture the correlation between diagnosis codes. Third, the lengthy clinical note leads to the excessive dispersion of key information related to codes. To tackle these challenges, we propose a novel framework to combine the inheritance-guided hierarchical assignment and co-occurrence graph propagation for clinical automatic diagnosis. Specifically, we propose a hierarchical joint prediction strategy to address the challenge of unbalanced codes distribution. Then, we utilize graph convolutional neural networks to obtain the correlation and semantic representations of medical ontology. Furthermore, we introduce multi attention mechanisms to extract crucial information. Finally, extensive experiments on MIMIC-III dataset clearly validate the effectiveness of our method.

cs.CL↗

arXiv2021

Summarising Historical Text in Modern Languages

We introduce the task of historical text summarisation, where documents in historical forms of a language are summarised in the corresponding modern language. This is a fundamentally important routine to historians and digital humanities researchers but has never been automated. We compile a high-quality gold-standard text summarisation dataset, which consists of historical German and Chinese news from hundreds of years ago summarised in modern German or Chinese. Based on cross-lingual transfer learning techniques, we propose a summarisation model that can be trained even with no cross-lingual (historical to modern) parallel data, and further benchmark it against state-of-the-art algorithms. We report automatic and human evaluations that distinguish the historic to modern language summarisation task from standard cross-lingual summarisation (i.e., modern to modern language), highlight the distinctness and value of our dataset, and demonstrate that our transfer learning approach outperforms standard cross-lingual benchmarks on this task.

cs.CL↗

arXiv2021

Magnetic field-induced thermal emission tuning of InSb-based metamaterials in the terahertz frequency regime

This work theoretically and analytically demonstrates the magnetic field-induced spectral radiative properties of photonic metamaterials incorporating both Indium Antimonide (InSb) and Tungsten (W) in the terahertz (THz) frequency regime. We have varied multiple factors of the nanostructures, including composite materials, layer thicknesses and surface grating fill factors, which impact the light-matter interactions and in turn modify the thermal emission of the metamaterials. We have proposed and validated a method for determining the spectral properties of InSb under an applied direct current (DC) magnetic field, and have employed this method to analyze how these properties can be dynamically tuned by modulating the magnitude of the field. For the first time, we have designed an InSb-W metamaterial exhibiting unity narrowband emission which can serve as an emitter for wavelengths around 55 $μ$m (approximately 5.5 THz). Additionally, the narrowband emission of this metamaterial can be magnetically tuned in both bandwidth and peak wavelength with a normal emissivity close to unity.

physics.optics↗

arXiv2021

A General 3D Non-Stationary Massive MIMO GBSM for 6G Communication Systems

A general three-dimensional (3D) non-stationary massive multiple-input multiple-output (MIMO) geometry-based stochastic model (GBSM) for the sixth generation (6G) communication systems is proposed in the paper. The novelty of the model is that the model is designed to cover a variety of channel characteristics, including space-time-frequency (STF) non-stationarity, spherical wavefront, spatial consistency, channel hardening, etc. Firstly, the introduction of the twin-cluster channel model is given in detail. Secondly, the key statistical properties such as space-time-frequency correlation function (STFCF), space cross-correlation function (CCF), temporal autocorrelation function (ACF), frequency correlation function (FCF), and performance indicators, e.g., singular value spread (SVS), and channel capacity are derived. Finally, the simulation results are given and consistent with some measurements in relevant literatures, which validate that the proposed channel model has a certain value as a reference to model massive MIMO channel characteristics.

eess.SP↗

arXiv2020

Manipulating Giant Rashba Valley Splitting and Quantum Hall States in Few-Layer Black Arsenic by Electrostatic Gating

Exciting phenomena may emerge in non-centrosymmetric two-dimensional (2D) electronic systems when spin-orbit coupling (SOC) interplays dynamically with Coulomb interactions, band topology, and external modulating forces, etc. Here, we report illuminating synergetic effects between SOC and Stark in centrosymmetric few-layer black arsenic (BAs), manifested as giant Rashba valley splitting and exotic quantum Hall states (QHS) reversibly controlled by electrostatic gating. The unusual finding is rooted in the puckering square lattice of BAs, in which heavy $4p$ orbitals form highly asymmetric $Γ$ valley with the $p_{z}$ symmetry and $D$ valleys of the $p_{x}$ origin, located at the Brillouin zone (BZ) center and near the time reversal invariant momenta of $X$, respectively. When the structure inversion symmetry is broken by perpendicular electric field, giant Rashba SOC is activated for the $p_{x}$ bands to produce strong spin-polarized $D^{+}$ and $D^{-}$ valleys related by time-reversal symmetry, coexisting with weak $Γ$ Rashba bands constrained by the $p_{z}$ symmetry. Intriguingly, strong Stark effect shows the same $p_{x}$-orbital selectiveness for $D$, collectively shifting the valence band maximum of $D^{\pm}$ valleys to exceed the $Γ$ pockets. Such an orchestrating effect between SOC and Stark allows us to realize gate-tunable spin valley manipulations for 2D hole gas, as revealed by unconventional magnetic field triggered even-to-odd transitions in QHS. For electron doping, the quantization of the $Γ$ Rashba bands is characterized by peculiar density-dependent transitions in band topology from two parabolic valleys to a unique inner-outer helical structure when charge carrier concentrations increase.

cond-mat.mes-hall↗

arXiv2020

Robustness of the pairwise kinematic Sunyaev-Zeldovich power spectrum shape as a cosmological gravity probe

We prove from the modified gravity (MG) galaxy/halo mock catalogs that the shape of the pairwise kinematic Sunyaev-Zeldovich (kSZ) power spectrum $P_{\rm kSZ}$ has constraining power on discriminating different gravity theories on cosmological scales. By varying the effective optical depth $τ_{\rm T}$ as a free parameter, we verify that the $τ_{\rm T}$-$f$ (the linear growth rate) degeneracy in the linear theory of $P_{\rm kSZ}$ is broken down by the non-linear structure growth and the scale-dependence of $f$ in some MG theories. Equivalently speaking, the shape of $P_{\rm kSZ}$ alone could be used to constrain the MG theories on cosmological scales. With a good knowledge of galaxy density biases, we verify that, a combination of the next generation of CMB and galaxy spectroscopic redshift surveys, e.g. BOSS+CMB-S4 or DESI+CMB-S4, could potentially discriminate $f(R)$ models from the general relativity at $\sim5σ$ level using the shape of the galaxy pairwise kSZ dipole $P_{{\rm kSZ},\ell=1}$ alone, when $f_{R0}=10^{-4}$.

astro-ph.CO↗

arXiv2020

Self-cleaning and self-cooling paper

The technique of passive daytime radiative cooling (PDRC) is used to cool an object down by simultaneously reflecting sunlight and thermally radiating heat to the cold outer space through the Earth's atmospheric window. However, for practical applications, current PDRC materials are facing unprecedented challenges such as complicated and expensive fabrication approaches and performance degradation arising from surface contamination. Here, we develop a scalable paper-based material with excellent self-cleaning and self-cooling capabilities, through air-spraying ethanolic polytetrafluoroethylene (PTFE) microparticles suspensions embedded within the micropores of the paper. The formed superhydrophobic PTFE coating not only protects the paper from water wetting and dust contamination for real-life applications but also reinforces its solar reflectance by sunlight backscattering. The paper fibers, when enhanced with PTFE particles, efficiently reflect sunlight and strongly radiate heat through the atmospheric window, resulting in a sub-ambient cooling performance of 5$^{\circ}$C and radiative cooling power of 104 W/m$^2$ under direct solar irradiance of 834 W/m$^2$ and 671 W/m$^2$, respectively. The self-cleaning surface of the cooling paper extends its lifespan and keep its good cooling performance for outdoor applications. Additionally, dyed papers are experimentally studied for broad engineering applications. They can absorb appropriate visible wavelengths to display specific colors and effectively reflect near-infrared lights to reduce solar heating, which synchronously achieves effective radiative cooling and aesthetic varieties in a cost-effective, scalable, and energy-efficient way.

physics.app-ph↗

arXiv2020

Spectrally Selective Solar Absorbers with High-temperature Insensitivity

It is of significance to incorporate spectral selectivity technology into solar thermal engineering, especially at high operational temperatures. This work demonstrates spectrally selective solar absorbers made of multilayer tungsten, silica, and alumina thin films that are angular insensitive and polarization-independent. An overall absorptance of 88.1% at solar irradiance wavelength, a low emittance of 7.0% at infrared thermal wavelength, and a high solar to heat efficiency of 79.9% are identified. Additionally, it shows the annealed samples maintain an extremely high absorption in solar radiation regime over at least 600 C and the solar absorbers after thermal annealing at 800 C still work well in a CSP system with an even high concentration factor of over 100.

physics.app-ph↗

arXiv2020

Using the Mark Weighted Correlation Functions to Improve the Constraints on Cosmological Parameters

We used the mark weighted correlation functions (MCFs), $W(s)$, to study the large scale structure of the Universe. We studied five types of MCFs with the weighting scheme $ρ^α$, where $ρ$ is the local density, and $α$ is taken as $-1,\ -0.5,\ 0,\ 0.5$, and 1. We found that different MCFs have very different amplitudes and scale-dependence. Some of the MCFs exhibit distinctive peaks and valleys that do not exist in the standard correlation functions. Their locations are robust against the redshifts and the background geometry, however it is unlikely that they can be used as ``standard rulers'' to probe the cosmic expansion history. Nonetheless we find that these features may be used to probe parameters related with the structure formation history, such as the values of $σ_8$ and the galaxy bias. Finally, after conducting a comprehensive analysis using the full shapes of the $W(s)$s and $W_{Δs}(μ)$s, we found that, combining different types of MCFs can significantly improve the cosmological parameter constraints. Compared with using only the standard correlation function, the combinations of MCFs with $α=0,\ 0.5,\ 1$ and $α=0,\ -1,\ -0.5,\ 0.5,\ 1$ can improve the constraints on $Ω_m$ and $w$ by $\approx30\%$ and $50\%$, respectively. We find highly significant evidence that MCFs can improve cosmological parameter constraints.

astro-ph.CO↗

arXiv2020

Harvesting Energy from Sun, Outer Space, and Soil

While solar power systems have offered a wide variety of electricity generation approaches including photovoltaics, solar thermal power systems, and solar thermoelectric generators, the ability of generating electricity at both the daytime and nighttime with no necessity of energy storage still remains challenging. Here, we propose and verify a strategy of harvesting solar energy by solar heating during the daytime and harnessing the coldness of the outer space through radiative cooling to produce electricity at night using a commercial thermoelectric module. It enables electricity generation for 24 hours a day. We experimentally demonstrate a peak power density of 37 mW/m2 at night and a peak value of 723 mW/m2 during the daytime. A theoretical model that accurately predicts the performance of the device is developed and validated. The feature of 24-hour electricity generation shows great potential energy applications of off-grid and battery-free lighting and sensing.

physics.app-ph↗

arXiv2020

Blackbody-cavity Ideal Solar Absorbers

Spectrally selective solar absorbers (SSAs), harvesting sunlight into heat, are the key to the concentrated solar thermal systems. Current SSAs' designs using photonic crystals, metamaterials, or cermets are either cost-inefficient or have limited applicability due to complicated nanofabrication methods and poor thermal stability at high temperatures. We present a scalable-manufactured blackbody cavity solar absorber design with nearly ideal properties. The unity solar absorptivity and nearly zero infrared emissivity allow for a stagnation temperature of 880C under 10 suns. The performance surpasses those state-of-the-art SSAs manufactured by nanofabrication methods. This design relies on traditional fabricating methods, such as machining, casting, and polishing. This makes it easy for large-scale industrial applications, and the "blackbody cavity" feature enables its fast-integration to existing concentrated solar thermal systems.

physics.app-ph↗

arXiv2020

Non-contact Thermal Transistor Effects Modulated by Nanoscale Mechanical Deformation

Thermal management has become a promising field in recent years due to the limitation of energy resources and the global warming. An important topic in improving the efficiency of thermal energy utilization is how to control the flows of heat, and thermal rectifiers, such as the thermal transistor, have been proposed as units for modulating the flow of heat. In this work, a reconfigurable non-contact thermal transistor with two-dimensional grating is introduced. The thermal transistor consists of three parts: source, gate, and drain, with the gate working around the phase-transition temperature of vanadium dioxide, a type of phase-transition material. Results show that the unit has a clear transistor-like behavior. The surface phonon/plasmon polaritons supported by the insulating/metallic states that contribute to the radiative thermal transport can be modulated at a nanoscale separation. And the dynamic amplification factor ranges from 15.4 to 30.6 when the stretchable polydimethylsiloxane is subjected to tension or compression. This work sheds light on studies about the controllable small-scale thermal transport due to mechanical deformations.

physics.app-ph↗

arXiv2020

Efficient Solar-driven Steam Generation Enabled by An Ultra-black Paint

Solar-driven interfacial steam generation for desalination has attracted broad attention. However, a significant challenge still remains for achieving a higher evaporation rate and high water quality, together with a cost-effective and easy-to-manufacture device to provide a feasible solar-driven steam generation system. In this study, a novel ultra-black paint, Black 3.0, serving as a perfect solar absorber is introduced into the hot-pressed melamine foam networks, allowing us to construct an ultra-black (99% absorptance in the solar region) and self-floating evaporation device. The high performing features of effective solar absorptance and salt-rejection capability contribute to a high-to-date evaporation rate of freshwater at 2.48 kg m-2 h-1 under one sun (1 kW m-2). This interfacial solar evaporator has a daily drinkable water yield of 2.8 kg m-2 even in cloudy winter weather and maintains stability in water with a wide range of acidity and alkalinity (pH 1~14). These features will enable the construction of a facilely fabricated, robust, highly-efficient, and cost-effective solar steam generation system for freshwater production.

physics.app-ph↗