arXiv subjects

Shengfeng Deng

Publications and source records attributed to Shengfeng Deng.

23 records · Page 2Linked to original sources

arXiv2022

Synchronization dynamics on the EU and US power grids

Dynamical simulation of the cascade failures on the EU and USA high-voltage power grids has been done via solving the second-order Kuramoto equation. We show that synchronization transition happens by increasing the global coupling parameter $K$ with metasatble states depending on the initial conditions so that hysteresis loops occur. We provide analytic results for the time dependence of frequency spread in the large $K$ approximation and by comparing it with numerics of $d=2,3$ lattices, we find agreement in the case of ordered initial conditions. However, different power-law (PL) tails occur, when the fluctuations are strong. After thermalizing the systems we allow a single line cut failure and follow the subsequent overloads with respect to threshold values $T$. The PDFs $p(N_f)$ of the cascade failures exhibit PL tails near the synchronization transition point $K_c$. Near $K_c$ the exponents of the PL-s for the US power grid vary with $T$ as $1.4 \le τ\le 2.1$, in agreement with the empirical blackout statistics, while on the EU power grid we find somewhat steeper PL-s characterized by $1.4 \le τ\le 2.4$. Below $K_c$ we find signatures of $T$-dependent PL-s, caused by frustrated synchronization, reminiscent of Griffiths effects. Here we also observe stability growth following the blackout cascades, similar to intentional islanding, but for $K > K_c$ this does not happen. For $T < T_c$, bumps appear in the PDFs with large mean values, known as "dragon king" blackout events. We also analyze the delaying/stabilizing effects of instantaneous feedback or increased dissipation and show how local synchronization behaves on geographic maps.

cond-mat.stat-mech↗

arXiv2020

Social distancing and epidemic resurgence in agent-based Susceptible-Infectious-Recovered models

Once an epidemic outbreak has been effectively contained through non-pharmaceutical interventions, a safe protocol is required for the subsequent release of social distancing restrictions to prevent a disastrous resurgence of the infection. We report individual-based numerical simulations of stochastic susceptible-infectious-recovered model variants on four distinct spatially organized lattice and network architectures wherein contact and mobility constraints are implemented. We robustly find that the intensity and spatial spread of the epidemic recurrence wave can be limited to a manageable extent provided release of these restrictions is delayed sufficiently (for a duration of at least thrice the time until the peak of the unmitigated outbreak) and long-distance connections are maintained on a low level (limited to less than five percent of the overall connectivity).

physics.soc-ph↗

arXiv2020

A coupled two-species model for the pair contact process with diffusion

The contact process with diffusion (PCPD) defined by the binary reactions 2 B -> 3 B, 2 B -> 0 and diffusive particle spreading exhibits an unusual active to absorbing phase transition whose universality class has long been disputed. Multiple studies have indicated that an explicit account of particle pair degrees of freedom may be required to properly capture this system's effective long-time, large-scale behavior. We introduce a two-species representation in which single particles B and pairs A are coupled according to the stochastic reactions B + B -> A, A -> A + B, A -> 0, and A -> B + B. Mean-field analysis reveals that the phase transition is driven by competition and balance between both species. We employ Monte Carlo simulations to demonstrate that this model captures the pertinent PCPD features. In the inactive phase, A particles rapidly go extinct, leaving the B species to undergo pure pair annihilation kinetics. At criticality, both A and B densities decay with the same exponents as the PCPD order parameters, and display mean-field scaling above the critical dimension 2. In one dimension, the critical exponents for the B species obtained from seed simulations agree well with previously reported exponent values. We demonstrate that the scaling properties of consecutive particle pairs in the PCPD are identical with that of the A species in the coupled model. This two-species picture resolves the conceptual difficulty for seed simulations in the original PCPD and naturally introduces multiple length and time scales, which cause strong corrections to scaling. The extracted moment ratios from our simulations indicate that our model displays the same temporal crossover behavior as the PCPD, which further corroborates its full dynamical equivalence with our coupled model.

cond-mat.stat-mech↗

arXiv2018

Active image restoration

We study active restoration of noise-corrupted images generated via the Gibbs probability of an Ising ferromagnet in external magnetic field. Ferromagnetism accounts for the prior expectation of data smoothness, i.e. a positive correlation between neighbouring pixels (Ising spins), while the magnetic field refers to the bias. The restoration is actively supervised by requesting the true values of certain pixels after a noisy observation. This additional information improves restoration of other pixels. The optimal strategy of active inference is not known for realistic (two-dimensional) images. We determine this strategy for the mean-field version of the model and show that it amounts to supervising the values of spins (pixels) that do not agree with the sign of the average magnetization. The strategy leads to a transparent analytical expression for the minimal Bayesian risk, and shows that there is a maximal number of pixels beyond of which the supervision is useless. We show numerically that this strategy applies for two-dimensional images away from the critical regime. Within this regime the strategy is outperformed by its local (adaptive) version, which supervises pixels that do not agree with their Bayesian estimate. We show on transparent examples how active supervising can be essential in recovering noise-corrupted images and advocate for a wider usage of active methods in image restoration.

cond-mat.stat-mech↗

arXiv2014

Optimal Transport in Worldwide Metro Networks

Metro networks serve as good examples of traffic systems for understanding the relations between geometric structures and transport properties.We study and compare 28 world major metro networks in terms of the Wasserstein distance, the key metric for optimal transport, and measures geometry related, e.g. fractal dimension, graph energy and graph spectral distance. The finding of power-law relationships between rescaled graph energy and fractal dimension for both unweighted and weighted metro networks indicates the energy costs per unit area are lower for higher dimensioned metros. In L space, the mean Wasserstein distance between any pair of connected stations is proportional to the fractal dimension, which is in the vicinity of our theoretical calculations treated on special regular tree graphs. This finding reveals the geometry of metro networks and tree graphs are in close proximity to one another. In P space, the mean Wasserstein distance between any pair of stations relates closely to the average number of transfers. By ranking several key quantities transport concerned, we obtain several ranking lists in which New York metro and Berlin metro consistently top the first two spots.

physics.soc-ph↗