arXiv subjects

Chong Li

Publications and source records attributed to Chong Li.

At least 127 records · Page 7Linked to original sources

arXiv2018

Online Cyber-Attack Detection in Smart Grid: A Reinforcement Learning Approach

Early detection of cyber-attacks is crucial for a safe and reliable operation of the smart grid. In the literature, outlier detection schemes making sample-by-sample decisions and online detection schemes requiring perfect attack models have been proposed. In this paper, we formulate the online attack/anomaly detection problem as a partially observable Markov decision process (POMDP) problem and propose a universal robust online detection algorithm using the framework of model-free reinforcement learning (RL) for POMDPs. Numerical studies illustrate the effectiveness of the proposed RL-based algorithm in timely and accurate detection of cyber-attacks targeting the smart grid.

cs.LG↗

arXiv2018

A large-scale survey of CO and its isotopologues toward the Rosette molecular cloud

Using the PMO-13.7m millimeter telescope at Delingha in China, we have conducted a large-scale simultaneous survey of $^{12}$CO, $^{13}$CO, and C$^{18}$O J=1-0 emission toward the Rosette molecular cloud (RMC) region with a sky coverage of 3.5 $\times$ 2.5 deg$^2$. The majority of the emission in the region comes from the RMC complex with velocities lying in the range from -2 km s$^{-1}$ to 20.5 km s$^{-1}$. Beyond this velocity range, 73 molecular clumps are identified with kinematic distances from 2.4 kpc to 11 kpc. Based on the spatial and velocity distribution, nine individual clouds, C1-C9, have been identified for the RMC complex. It appears that the C3 cloud is different from other clouds in the RMC complex in view of its characteristic velocity, excitation temperature, and velocity dispersion. Most of the young stellar clusters in the region are located in positions of both high column density and high excitation temperature. Seven new molecular filaments are discovered in the RMC complex. Evidence for cloud-cloud collision is found in the region of young stellar clusters REFL9 and PouF, showing that these young stellar clusters probably result from a cloud-cloud collision. The abundance ratios of $^{13}$CO to C$^{18}$O in the region have a mean value of 13.7 which is 2.5 times larger than the solar system value, showing that UV photons from the nearby OB clusters have strong influence on the chemistry of clouds in the RMC complex.

astro-ph.GA↗

arXiv2018

Multi-task Learning for Continuous Control

Reliable and effective multi-task learning is a prerequisite for the development of robotic agents that can quickly learn to accomplish related, everyday tasks. However, in the reinforcement learning domain, multi-task learning has not exhibited the same level of success as in other domains, such as computer vision. In addition, most reinforcement learning research on multi-task learning has been focused on discrete action spaces, which are not used for robotic control in the real-world. In this work, we apply multi-task learning methods to continuous action spaces and benchmark their performance on a series of simulated continuous control tasks. Most notably, we show that multi-task learning outperforms our baselines and alternative knowledge sharing methods.

cs.LG↗

arXiv2018

Secrecy Capacity of Colored Gaussian Noise Channels with Feedback

In this paper, the k-th order autoregressive moving average (ARMA(k)) Gaussian wiretap channel with noiseless causal feedback is considered, in which an eavesdropper receives noisy observations of the signals in both forward and feedback channels. It is shown that a variant of the generalized Schalkwijk-Kailath scheme, a capacity-achieving coding scheme for the feedback Gaussian channel, achieves the same maximum rate for the same channel with the presence of an eavesdropper. Therefore, the secrecy capacity is equal to the feedback capacity without the presence of an eavesdropper for the feedback channel. Furthermore, the results are extended to the additive white Gaussian noise (AWGN) channel with quantized feedback. It is shown that the proposed coding scheme achieves a positive secrecy rate. As the amplitude of the quantization noise decreases to zero, the secrecy rate converges to the capacity of the AWGN channel.

cs.IT↗

arXiv2018

Youla Coding and Computation of Gaussian Feedback Capacity

In this paper, we propose an approach to numerically compute the feedback capacity of stationary finite dimensional Gaussian channels and construct (arbitrarily close to) capacity-achieving feedback codes. In particular, we first extend the interpretation of feedback communication over stationary finite dimensional Gaussian channels as feedback control systems by showing that, the problem of finding stabilizing feedback controllers with maximal reliable transmission rate over Youla parameters coincides with the problem of finding strictly causal filters to achieve feedback capacity derived in [2]. This extended interpretation provides an approach to construct deterministic feedback coding schemes with double exponential decaying error probability. We next propose asymptotic capacity-achieving upper bounds, which can be numerically evaluated by solving finite dimensional convex optimizations. From the filters that achieve the upper bounds, we apply the Youla-based interpretation to construct feasible filters, i.e., feedback codes, leading to a sequence of lower bounds. We prove the sequence of lower bounds is asymptotically capacity-achieving.

cs.IT↗

arXiv2018

Equilibrium problems on Riemannian manifolds with applications

We study the equilibrium problem on general Riemannian manifolds. The results on existence of solutions and on the convex structure of the solution set are established. Our approach consists in relating the equilibrium problem to a suitable variational inequality problem on Riemannian manifolds, and is completely different from previous ones on this topic in the literature. As applications, the corresponding results for the mixed variational inequality and the Nash equilibrium are obtained. Moreover, we formulate and analyze the convergence of the proximal point algorithm for the equilibrium problem. In particular, correct proofs are provided for the results claimed in J. Math. Anal. Appl. 388, 61-77, 2012 (i.e., Theorems 3.5 and 4.9 there) regarding the existence of the mixed variational inequality and the domain of the resolvent for the equilibrium problem on Hadamard manifolds.

math.OC↗

arXiv2017

Asymmetrical interaction induced real spectra and exceptional points in a non-Hermitian Hamiltonian

Non-Hermitian systems with parity-time symmetry have been developed rapidly and hold great promise for future applications. Unlike most existing works considering the symmetry of the free energy terms (e.g., gain-loss system), in this paper, we report that a realizable non-Hermitian interaction between two quantum resonances can also have a real spectrum after the exceptional point. That phenomenon is similar with that in the gain-loss system so that the non-Hermitian interaction can be an excellent substitute for quantum gain. Such a non-Hermitian interaction can be realized in designed optomechanics, and we find that its dynamics are in accordance with those of normal gain system as expected. As examples, the phase transition near the exceptional point and the induced chaos in weak nonlinear coupling are shown and analyzed for an intuitive visual. Our results provide a platform for realizing parity-time symmetry devices and studying properties of non-Hermitian quantum mechanics.

quant-ph↗

arXiv2017

Linear convergence of inexact descent method and inexact proximal gradient algorithms for lower-order regularization problems

The $\ell_p$ regularization problem with $0< p< 1$ has been widely studied for finding sparse solutions of linear inverse problems and gained successful applications in various mathematics and applied science fields. The proximal gradient algorithm is one of the most popular algorithms for solving the $\ell_p$ regularisation problem. In the present paper, we investigate the linear convergence issue of one inexact descent method and two inexact proximal gradient algorithms (PGA). For this purpose, an optimality condition theorem is explored to provide the equivalences among a local minimum, second-order optimality condition and second-order growth property of the $\ell_p$ regularization problem. By virtue of the second-order optimality condition and second-order growth property, we establish the linear convergence properties of the inexact descent method and inexact PGAs under some simple assumptions. Both linear convergence to a local minimal value and linear convergence to a local minimum are provided. Finally, the linear convergence results of the inexact numerical methods are extended to the infinite-dimensional Hilbert spaces.

math.OC↗

arXiv2017

Creation of Half-metallic f -orbital Dirac Fermion with Superlight Elements in Orbital-Designed Molecular Lattice

Magnetism in solids generally originates from the localized $d$- or $f$-orbitals that are hosted by heavy transition-metal elements. Here, we demonstrate a novel mechanism for designing half-metallic $f$-orbital Dirac fermion from superlight $sp$-elements. Combining first-principles and model calculations, we show that bare and flat-band-sandwiched (FBS) Dirac bands can be created when C$_{20}$ molecules are deposited into a 2D hexagonal lattice, which are composed of $f$-molecular orbitals (MOs) derived from $sp$-atomic orbitals (AOs). Furthermore, charge doping of the FBS Dirac bands induces spontaneous spin-polarization, converting the system into a half-metallic Dirac state. Based on this discovery, a model of spin field effect transistor is proposed to generate and transport 100\% spin-polarized carriers. Our finding illustrates a novel concept to realize exotic quantum states by manipulating MOs, instead of AOs, in orbital-designed molecular crystal lattices.

cond-mat.mes-hall↗

arXiv2017

Solid-to-super Critical Phase Change during Laser Internal Ablation

The mechanisms of phase change of argon during picosecond laser internal ablation are studied using molecular dynamics simulations. It is found that propagation of stress wave and fluctuation of temperature are periodical. The phase change process from solid to liquid to supercritical fluid then back to solid occurs as combined results of heating and the propagation of tensile stress wave induced by the laser pulse and the limited internal space.

physics.atm-clus↗

arXiv2017

Molecular Environments of Three Large Supernova Remnants in the Third Galactic Quadrant: G205.5+0.5, G206.9+2.3, and G213.0-0.6

We present CO observations toward three large supernova remnants (SNRs) in the third Galactic quadrant using the Purple Mountain Observatory Delingha 13.7m radio telescope. The observations are part of the high-resolution CO survey of the Galactic plane between Galactic longitudes l=-10deg to 250deg and latitudes b=-5deg to 5d. CO emission was detected toward the three SNRs: G205.5+0.5 (Monoceros Nebula), G206.9+2.3 (PKS 0646+06), and G213.0-0.6. Both of SNRs G205.5+0.5 and G213.0-0.6 exhibit the morphological agreement (or spatial correspondences) between the remnant and the surrounding molecular clouds (MCs), as well as kinematic signatures of shock perturbation in the molecular gas. We confirm that the two SNRs are physically associated with their ambient MCs and the shock of SNRs is interacting with the dense, clumpy molecular gas. SNR G206.9+2.3, which is close to the northeastern edge of the Monoceros Nebula, displays the spatial coincidence with molecular partial shell structures at VLSR~15km/s. While no significant line broadening has been detected within or near the remnant, the strong morphological correspondence between the SNR and the molecular cavity implies that SNR G206.9+2.3 is probably associated with these CO gas and is evolving in the low-density environment. The physical features of individual SNRs, together with the relationship between SNRs and their nearby objects, are also discussed.

astro-ph.GA↗

arXiv2016

Realization and application of parity-time-symmetric oscillators in quantum regime

Although people have already artificially formed parity--time ($\mathcal{PT}$) symmetry with gain and loss in a balanced manner, it is still a defect that the gain is restricted to semi--classical but not full quantum. Here we propose and analyze a theoretical scheme to realize full quantum oscillator $\mathcal{PT}$--symmetry. The quantum gain is provided by a dissipation optical cavity with blue detuned laser field. After adiabatically eliminating the cavity modes, we give an effective master equation, which is a more complete quantum description compared with non--Hermitian Hamiltonian, to reveal the quantum behaviors of such a gain oscillator. This kind of $\mathcal{PT}$--symmetry can eliminate the dissipation effect in quantum regime. As examples, we finally apply $\mathcal{PT}$--symmetric oscillators to enhance optomechanically induced transparency and to preserve oscillator non--classical state.

quant-ph↗

arXiv2016

Flexible and experimentally feasible shortcut to quantum Zeno dynamic passage

We propose and discuss a theoretical scheme to speed up Zeno dynamic passage by an external acceleration Hamiltonian. This scheme is a flexible and experimentally feasible acceleration because the acceleration Hamiltonian does not adhere rigidly to an invariant relationship, whereas it can be a more general form $\sum u_{j}(t)H_{cj}$. Here $H_{cj}$ can be arbitrarily selected without any limitation, and therefore one can always construct an acceleration Hamiltonian by only using realizable $H_{cj}$. Applying our scheme, we finally design an experimentally feasible Hamiltonian as an example to speed up an entanglement preparation passage.

quant-ph↗

arXiv2016

The Distant Outer Gas Arm Between l=35d and l=45d

The Galactic plane has been mapped from l=34.75d to 45.25d and b=-5.25d to 5.25d in the CO (J=1-0) emission with the 13.7 m telescope of the Purple Mountain Observatory. The unbiased survey covers a large area of 100 square degrees sampled every 30" with a velocity resolution of ~0.2km/s. In this paper, we present the result of an unbiased CO survey of this longitude and latitude range in the velocity range from -60km/s to -10km/s. Over 500 molecular clouds (MCs) are picked out from the 12CO emission, and 131 of these MCs are associated with 13CO emission.The distant MCs, which lie beyond the solar circle and are mostly concentrated in the Galactic plane, trace the large-scale molecular gas structure over 10 degrees of Galactic azimuth. We suggest that the CO emission of the segment is from the Outer Arm. The physical mid-plane traced by the Outer Arm seems to be slightly displaced from the IAU-defined plane on a large scale, which could be explained by the warped plane at large Galactocentric distances of >~10 kpc and the apparent tilted mid-plane to the projected IAU-defined plane caused by the Sun's z-height above the disk for distances near and within the Solar circle. If the inner plane of our Galaxy is flat, we can derive an upper limit of the Sun's offset of ~17.1 pc above the physical mid-plane of the Milky Way. We also discuss the correlations between the physical parameters of the distant MCs, which is quite consistent with the result of other studies of this parameter.

astro-ph.GA↗

arXiv2016

Quantum synchronization and quantum state sharing in irregular complex network

We investigate quantum synchronization phenomenon within the complex network constituted by coupled optomechanical systems and prove the unknown identical quantum states can be shared or distributed in the quantum network even though the topology is varying. Considering a channel constructed by quantum correlation, we show that quantum synchronization can sustain and maintain high levels in Markovian dissipation for a long time. We analyze state sharing process between two typical complex networks, that is, a small-world network corresponding to linear motif state sharing and a scale-free network corresponding to whole network sharing, respectively. Our results predict that linked nodes can be directly synchronized in small-world network, but the whole network will be synchronized only if some specific synchronization conditions are satisfied. Furthermore, we give the synchronization conditions analytically through analyzing network dynamics. This proposal paves the way for studying multi-interaction synchronization and achieving an effective quantum information processing in complex network.

quant-ph↗

arXiv2016

Group sparse optimization via $\ell_{p,q}$ regularization

In this paper, we investigate a group sparse optimization problem via $\ell_{p,q}$ regularization in three aspects: theory, algorithm and application. In the theoretical aspect, by introducing a notion of group restricted eigenvalue condition, we establish some oracle property and a global recovery bound of order $O(λ^\frac{2}{2-q})$ for any point in a level set of the $\ell_{p,q}$ regularization problem, and by virtue of modern variational analysis techniques, we also provide a local analysis of recovery bound of order $O(λ^2)$ for a path of local minima. In the algorithmic aspect, we apply the well-known proximal gradient method to solve the $\ell_{p,q}$ regularization problems, either by analytically solving some specific $\ell_{p,q}$ regularization subproblems, or by using the Newton method to solve general $\ell_{p,q}$ regularization subproblems. In particular, we establish the linear convergence rate of the proximal gradient method for solving the $\ell_{1,q}$ regularization problem under some mild conditions. As a consequence, the linear convergence rate of proximal gradient method for solving the usual $\ell_{q}$ regularization problem ($0<q<1$) is obtained. Finally in the aspect of application, we present some numerical results on both the simulated data and the real data in gene transcriptional regulation.

math.OC↗

arXiv2015

Single-photon Quantum Router by Two Distant Artificial Atoms

Nowadays, quantum router is playing a key role in quantum communication and quantum network- s. Here we propose a tunable single-photon routing scheme, based on quantum interference, which uses two distant artificial atoms coupling to two transmission lines. Depending on the distance between the two atoms, the collective effect will lead to destructive or constructive interference between the scattered photons. Under standing wave condition, single photon from the incident channel can be perfectly transmitted or redirected into another channel by asymmetric or symmet- ric reflected phase shift of atoms, respectively. Therefore, we show that our router can be controlled by adjusting the detuning of the atoms and interatomic distance, without any classical field.

quant-ph↗

arXiv2015

Optimization of broadband omnidirectional antireflection coatings for solar cells

Broadband and omnidirectional antireflection coating is a generally effective way to improve solar cell efficiency, because the destructive interference between the reflected and input waves could maximize transmission light in the absorption layer. Several theoretical calculations have been developed to optimize the anti-reflective coating to maximize the average transmittance. However, the solar irradiances of the clear sky spectral direct beam on a receiver plane at different positions and times are variable greatly. Here we report a new theoretical calculation of anti-reflective coating with incident quantum efficiency ηin as evaluation function for practical application. The two-layer and three-layer anti-reflective coatings are optimized over λ = [300, 1100] nm and θ = [0°, 90°] for cities of Quito, Beijing and Moscow. The ηin of two-layer anti-reflective coating increases by 0.26%, 1.37% and 4.24% for these 3 cities, respectively, compared with that other theoretical calculations due to better match between the local actual solar spectrum and quantum efficiency spectrum. Our numerical simulation and comparison data with other optimization methods suggest that this optimization method combining ant colony algorithm method with SPCTRL2 solar spectral irradiance can effectively push the efficient solar cell toward higher quantum efficiency, thus enabling high utilization efficiency of solar irradiance.

physics.optics↗