arXiv subjects

Li Huang

Publications and source records attributed to Li Huang.

At least 127 records · Page 7Linked to original sources

arXiv2019

Formal Analysis of Hybrid-Dynamic Timing Behaviors in Cyber-Physical Systems

Ensuring correctness of timed behaviors in cyber-physical systems (CPS) using closed-loop verification is challenging due to the hybrid dynamics in both systems and environments. Simulink and Stateflow are tools for model-based design that support a variety of mechanisms for modeling and analyzing hybrid dynamics of real-time embedded systems. In this paper, we present an SMT-based approach for formal analysis of the hybrid-dynamic timing behaviors of CPS modeled in Simulink blocks and Stateflow states (S/S). The hierarchically interconnected S/S are flattened and translated into the input language of SMT solver for formal verification. A translation algorithm is provided to facilitate the translation. Formal verification of timing constraints against the S/S models is reduced to the validity checking of the resulting SMT encodings. The applicability of our approach is demonstrated on an unmanned surface vessel case study.

cs.SE↗

arXiv2019

Formal Verification of Dynamic and Stochastic Behaviors for Automotive Systems

Formal analysis of functional and non-functional requirements is crucial in automotive systems. The behaviors of those systems often rely on complex dynamics as well as on stochastic behaviors. We have proposed a probabilistic extension of Clock Constraint Specification Language, called PrCCSL,for specification of (non)-functional requirements and proved the correctness of requirements by mapping the semantics of the specifications into UPPAAL models. Previous work is extended in this paper by including an extension of PrCCSL, called PrCCSL*, for specification of stochastic and dynamic system behaviors, as well as complex requirements related to multiple events. To formally analyze the system behaviors/requirements specified in PrCCSL*, the PrCCSL* specifications are translated into stochastic UPPAAL models for formal verification. We implement an automatic translation tool, namely ProTL, which can also perform formal analysis on PrCCSL* specifications using UPPAAL-SMC as an analysis backend. Our approach is demonstrated on two automotive systems case studies.

cs.SE↗

arXiv2019

Magnetic order induced polarization anomaly of Raman scattering in 2D magnet CrI$_3$

The recent discovery of 2D magnets has revealed various intriguing phenomena due to the coupling between spin and other degree of freedoms (such as helical photoluminescence, nonreciprocal SHG). Previous research on the spin-phonon coupling effect mainly focuses on the renormalization of phonon frequency. Here we demonstrate that the Raman polarization selection rules of optical phonons can be greatly modified by the magnetic ordering in 2D magnet CrI$_3$. For monolayer samples, the dominant A$\rm_{1g}$ peak shows abnormally high intensity in the cross polarization channel at low temperature, which is forbidden by the selection rule based on the lattice symmetry. While for bilayer, this peak is absent in the cross polarization channel for the layered antiferromagnetic (AFM) state and reappears when it is tuned to the ferromagnetic (FM) state by an external magnetic field. Our findings shed light on exploring the emergent magneto-optical effects in 2D magnets.

cond-mat.mes-hall↗

arXiv2019

SMT-based Probabilistic Analysis of Timing Constraints in Cyber-Physical Systems

Modeling and analysis of timing constraints is crucial in cyber-physical systems (CPS). EAST-ADL is an architectural language dedicated to safety-critical embedded system design. SIMULINK/STATEFLOW (S/S) is a widely used industrial tool for modeling and analysis of embedded systems. In most cases, a bounded number of violations of timing constraints in systems would not lead to system failures when the results of the violations are negligible, called Weakly-Hard (WH). We have previously defined a probabilistic extension of Clock Constraint Specification Language (CCSL), called PrCCSL, for formal specification of EAST-ADL timing constraints in the context of WH. In this paper, we propose an SMT-based approach for probabilistic analysis of EAST-ADL timing constraints in CPS modeled in S/S: an automatic transformation from S/S models to the input language of SMT solver is provided; timing constraints specified in PrCCSL are encoded into SMT formulas and the probabilistic analysis of timing constraints is reduced to the validity checking of the resulting SMT encodings. Our approach is demonstrated a cooperative automotive system case study.

cs.SE↗

arXiv2019

Patient Clustering Improves Efficiency of Federated Machine Learning to predict mortality and hospital stay time using distributed Electronic Medical Records

Electronic medical records (EMRs) supports the development of machine learning algorithms for predicting disease incidence, patient response to treatment, and other healthcare events. But insofar most algorithms have been centralized, taking little account of the decentralized, non-identically independently distributed (non-IID), and privacy-sensitive characteristics of EMRs that can complicate data collection, sharing and learning. To address this challenge, we introduced a community-based federated machine learning (CBFL) algorithm and evaluated it on non-IID ICU EMRs. Our algorithm clustered the distributed data into clinically meaningful communities that captured similar diagnoses and geological locations, and learnt one model for each community. Throughout the learning process, the data was kept local on hospitals, while locally-computed results were aggregated on a server. Evaluation results show that CBFL outperformed the baseline FL algorithm in terms of Area Under the Receiver Operating Characteristic Curve (ROC AUC), Area Under the Precision-Recall Curve (PR AUC), and communication cost between hospitals and the server. Furthermore, communities' performance difference could be explained by how dissimilar one community was to others.

cs.LG↗

arXiv2019

Pressure-controlled Structural Symmetry Transition in Layered InSe

Structural symmetry of crystals plays important roles in physical properties of two-dimensional (2D) materials, particularly in the nonlinear optics regime. It has been a long-term exploration on the physical properties in 2D materials with various stacking structures, which correspond to different structural symmetries. Usually, the manipulation of rotational alignment between layers in 2D heterostructures has been realized at the synthetic stage through artificial stacking like assembling Lego bricks. However, the reconfigurable control of translational symmetry of crystalline structure is still challenging. High pressure, as a powerful external control knob, provides a very promising route to circumvent this constraint. Here, we experimentally demonstrate a pressure-controlled symmetry transition in layered InSe. The continuous and reversible evolution of structural symmetries can be in-situ monitored by using the polarization-resolved second harmonic generation (SHG) spectroscopy. As pressure changes, the reconfigurable symmetry transition of the SHG pattern from three-fold rotational symmetry to mirror symmetry was experimentally observed in a layered InSe samples and was successfully explained by the proposed interlayer-translation model. This opens new routes towards potential applications of manipulating crystal symmetry of 2D materials.

physics.optics↗

arXiv2019

Implementing the inverse type-II seesaw mechanism into the 3-3-1 model

After the LHC is turning on and accumulating more data, the TeV scale seesaw mechanisms for small neutrino masses in the form of inverse seesaw mechanisms are gaining more and more attention once they provide neutrino masses at sub-eV scale and can be probed at the LHC. Here we restrict our investigation to the inverse type II seesaw case and implement it into the framework of the 3-3-1 model with right-handed neutrinos. As interesting result, the mechanism provides small masses to both the standard neutrinos as well as to the right-handed ones. Its best signature are the doubly charged scalars which are sextet by the 3-3-1 symmetry. We investigate their production at the LHC through the process $σ(p\,p \rightarrow Z^*, γ^* ,Z^{\prime} \rightarrow Δ^{++}\,Δ^{--})$ and their signal through four leptons final state decay channel.

hep-ph↗

arXiv2018

Six Top Messages of New Physics at the LHC

Six top signatures provide a novel probe of new physics. We discuss production of six top quarks as the decay products of a pair of top partners in the setting of a composite Higgs model, and argue that the six top signal may generically provide one of the first final states to show a discrepancy. We construct an analysis based on quantities such as $H_T$ and the numbers of jets which are tagged as boosted tops, $W$s, or containing $b$-tags, and show that the LHC with 3~ab$^{-1}$ can discover top partners with masses up to around 2.5 TeV in the six top signature.

hep-ph↗

arXiv2018

Modelling China's Credit System with Complex Network Theory for Systematic Credit Risk Control

The insufficient understanding of the credit network structure was recognized as a key factor for regulators' underestimation of the destructive systematic risk during the financial crisis that started in 2007. The existing credit network research either took a macro perspective to clarify the topological properties of financial systems at a descriptive level or analyzed the risk transmission path and characteristics of individual entities with much pre-assumptions of the network. Here, we used the theory of complex network to model China's credit system from 2000 to 2014 based on actual financial data. A bipartite financial institution-firm network and its projected sub-networks were constructed for an integrated analysis from both macro and micro perspectives, and the relationship between typological properties and systematic credit risk control was also explored. The typological analysis of the networks suggested that the financial institutions and firms were highly but asymmetrically connected, and the credit network structure made local idiosyncratic shocks possible to proliferate through the whole economy. In addition, the Chinese credit market was still dominated by state-owned financial institutions with firms competing fiercely for financial resources in the past fifteen years. Furthermore, the credit risk score (CRS) was introduced by simulation to identify the systematically important vertices in terms of systematic risk control. The results indicated that the vertices with more access to the credit market or less likelihood to be a bridge in the network were the ones with higher systematically importance. The empirical results from this study would provide specific policy suggestions to financial regulators on supervisory approaches and optimizing the allocation of regulatory resources to enhance the robustness of credit systems in China and in other countries.

q-fin.RM↗

arXiv2018

Mg$_{3+δ}$Sb$_x$Bi$_{2-x}$ family: A promising substitute for the start-of-art n-type thermoelectric materials near room temperature

Bi2Te3-xSex family has been the n-type start-of-the-art thermoelectric materials near room temperatures (RT) for more than half-century, which dominates the active cooling and novel waves harvesting application near RT. However, the drawbacks of brittle nature and Te-containing restrict the further applications exploring. Here, we show that a Mg3+δSbxBi2-x family ((ZT)avg =1.05) could be a promising substitute for the Bi2Te3-xSex family ((ZT)avg =0.9-1.0) in the temperature range of 50-250 °C based on the comparable thermoelectric performance through a synergistic effect from the tunable band gap using the alloy effect and the suppressible Mg-vacancy formation using interstitial Mn dopant. The former is to shift the optimal thermoelectric performance to near RT, and latter is helpful to partially decouple the electrical transport and thermal transport in order to get an optimal RT power factor. A positive temperature-dependence of band gap suggested this family is also a superior medium-temperature thermoelectric material for the significantly suppressed bipolar effect. Furthermore, a two times higher mechanical toughness, compared with Bi2Te3-xSex family, consolidates the promising substitute for the start-of-art n-type thermoelectric materials near RT.

cond-mat.mtrl-sci↗

arXiv2018

Natural Orbital-Based Lanczos Method for Anderson Impurity Models

We implement the Lanczos algorithm on natural orbital basis to solve the zero-temperature Green's function of Anderson impurity models, following the work of Y. Lu, M. Höppner, O. Gunnarsson, and M. W. Haverkort, Phys. Rev. B {\bf 90} (2014) 085102. We present the technical details, generalize the algorithm to the cases of particle-hole asymmetry, with local magnetic field, and of two impurities. The results are benchmarked with conventional Lanczos, quantum Monte Carlo, and numerical renormalization group methods, demonstrating its potential as a powerful impurity solver for the dynamical mean-field theory.

cond-mat.str-el↗

arXiv2018

Naturalness Sum Rules and Their Collider Tests

We present the most general sum rules reflecting the cancellation of ultraviolet divergences in the Higgs potential in weakly-coupled, natural extensions of the Standard Model. There is a separate sum rule for the cancellation of the quadratic and logarithmic divergences, and their forms depend on whether the divergences are canceled by same-spin or opposite-spin partners. These sum rules can be applied to mass eigenstates and conveniently used for direct collider tests of naturalness. We study in detail the feasibility of testing these sum rules in the top sector at a future $100\TeV$ proton collider within two benchmark models, the Little Higgs (LH) and the Maximally Symmetric Composite Higgs (MSCH). We show how the two ingredients of the sum rules, the top partner masses and their Yukawa couplings to the Higgs, can be measured with sufficient accuracy to provide a highly non-trivial quantitative test of the sum rules. In particular, we study observables sensitive to the sign of the top partner Yukawa, which is crucial for verifying the sum rules but is notoriously difficult to measure. We demonstrate that in the benchmark models under study, a statistically significant discrimination between the two possible signs of each Yukawa will be feasible with a 30 ab$^{-1}$ data set at $100\TeV$.

hep-ph↗

arXiv2018

Effective Coulomb interaction in actinides from linear response approach

The effective on-site Coulomb interaction (Hubbard $U$) between 5$f$ electrons in actinide metals (Th-Cf) is calculated with the framework of density-functional theory (DFT) using linear response approach. The $U$ values seldom rely on the exchange-correlation functional, spin-orbital coupling, and magnetic states, but depend on the lattice volume and actinide element. Along the actinide series, the Coulomb parameter $U$ of $α$-phase first decreases slowly, followed by a jump in the vicinity of Pu and then a monotonous increase. For light actinides, the lattice volume has a sizeable influence on $U$ while the localization of 5$f$ electrons is almost constant. But for transplutonium metals, $U$ is almost independent of the lattice volume but the electronic localization increases rapidly. The calculated lattice parameters from DFT+$U$ with the Coulomb parameters as input are in better agreement with the experimental values than those from DFT within local density approximation or Perdew-Burke-Ernzerhof approximation for solids (PBEsol). In particular, the agreement between PBEsol+$U$ and experiment is remarkable. We show that PBEsol+$U$ also well reproduce the experimental bulk moduli and the transition from itinerancy to localization of 5$f$ electrons along the series. Therefore it is concluded that DFT+$U$ with $U$ calculated from linear response approach is suitable for a good description of actinide metals.

cond-mat.mtrl-sci↗

arXiv2018

Itinerant-localized crossover and orbital dependent correlations for 4$f$ electrons in cerium-based ternary 122 compounds

The electronic structures of cerium-based ternary 122 compounds Ce$M_{2}$Si$_{2}$, where $M =$ Ru, Rh, Pd, and Ag, are investigated systematically by using the density functional theory in combination with the single-site dynamical mean-field theory. The momentum-resolved spectral functions, total and 4$f$ partial density of states, self-energy functions, and valence state fluctuations are calculated. The obtained results are in good accord with the available experimental data. It is suggested that, upon increasing atomic number from Ru to Ag, the 4$f$ electrons should become increasingly localized. An itinerant-localized crossover for 4$f$ electrons driven by chemical pressure may emerge when $M$ changes from Pd to Ag. Particularly, according to the low-frequency behaviors of 4$f$ self-energy functions, we identify an orbital selective 4$f$ insulating state in CeAg$_{2}$Si$_{2}$, which is totally unexpected.

cond-mat.str-el↗

arXiv2018

Pressure-Driven 5$f$ Localized-Itinerant Transition and Valence Fluctuation in Californium

A combination of the density functional theory and the single-site dynamical mean-field theory is employed to study the pressure dependence of electronic structure for cubic phase californium. We predict that its 5$f$ electrons could undergo an orbital-selective localized-itinerant transition under moderate pressure. The volume contraction causes remarkable charge redistribution and valence fluctuation behaviors, which are the driving forces of the divalent-trivalent transition. Additionally, we find that the angular momentum coupling mechanism is hardly affected by pressure. The 5$f$ orbital occupancy is well described by the intermediate coupling scheme.

cond-mat.str-el↗

arXiv2018

Electronic structure of cerium: A comprehensive first-principles study

Cerium, in which the 4$f$ valence electrons live at the brink between localized and itinerant characters, exhibits varying crystal structures and therefore anomalous physical properties with respect to temperature and pressure. Understanding its electronic structure and related lattice properties is one of the central topics in condensed matter theory. In the present work, we employed the state-of-the-art first-principles many-body approach (i.e., the density functional theory in combination with the single-site dynamical mean-field theory) to study its electronic structure thoroughly. The momentum-resolved spectral functions, total and $4f$ partial density of states, optical conductivities, self-energy functions, and atomic eigenstate histograms for cerium's four allotropes under ambient pressure were calculated and analyzed carefully. The calculated results demonstrate that the 4$f$ electrons in the $α$, $β$, $γ$, and $δ$ phases are all correlated with heavily remormalized electron masses. In the $α$ phase, the 4$f$ electrons tend to be itinerant, which cause strong hybridization between the 4$f$ and $spd$ bands and remarkable 4$f$ valence state fluctuation. While for the other phases, the 4$f$ electrons are close to be localized. Our calculated results support the Kondo volume collapse scenario for the cerium $α-γ$ transition. Finally, we examined the site dependence of $4f$ electronic structure in the $β$ phase. The calculated results suggest that it doesn't exhibit a site selective 4$f$ localized state, contrary to previous prediction.

cond-mat.str-el↗

arXiv2018

Efficient Parallel Self-Assembly Under Uniform Control Inputs

We prove that by successively combining subassemblies, we can achieve sublinear construction times for "staged" assembly of micro-scale objects from a large number of tiny particles, for vast classes of shapes; this is a significant advance in the context of programmable matter and self-assembly for building high-yield micro-factories.The underlying model has particles moving under the influence of uniform external forces until they hit an obstacle; particles bond when forced together with a compatible particle. Previous work considered sequential composition of objects, resulting in construction time that is linear in the number N of particles, which is inefficient for large N. Our progress implies critical speedup for constructible shapes; for convex polyominoes, even a constant construction time is possible. We also show that our construction process can be used for pipelining, resulting in an amortized constant production time.

cs.CG↗

arXiv2018

Probabilistic Analysis of Weakly-Hard Real-Time Systems

Modeling and analysis of non-functional properties, such as timing constraints, is crucial in automotive real-time embedded systems. EAST-ADL is a domain specific architectural language dedicated to safetycritical automotive embedded system design. We have previously specified EAST-ADL timing constraints in Clock Constraint Specification Language (CCSL) and proved the correctness of specification by mapping the semantics of the constraints into Uppaal models amenable to model checking. In most cases, a bounded number of violations of timing constraints in automotive systems would not lead to system failures when the results of the violations are negligible, called Weakly-Hard (WH). Previous work is extended in this paper by including support for probabilistic analysis of timing constraints in the context of WH: Probabilistic extension of CCSL, called PrCCSL, is defined and the EAST-ADL timing constraints with stochastic properties are specified in PrCCSL. The semantics of the extended constraints in PrCCSL is translated into Uppaal-SMC models for formal verification. Furthermore, a set of mapping rules is proposed to facilitate guarantee of translation. Our approach is demonstrated on an autonomous traffic sign recognition vehicle case study.

cs.SE↗