Helical damping and anomalous critical non-Hermitian skin effect

Non-Hermitian skin effect and critical skin effect are unique features of non-Hermitian systems. In this Letter, we study an open system with its dynamics of single-particle correlation function effectively dominated by a non-Hermitian damping matrix, which exhibits $\mathbb{Z}_2$ skin effect, and uncover the existence of a novel phenomenon of helical damping. When adding perturbations that break anomalous time reversal symmetry to the system, the critical skin effect occurs, which causes the disappearance of the helical damping in the thermodynamic limit although it can exist in small size systems. We also demonstrate the existence of anomalous critical skin effect when we couple two identical systems with $\mathbb{Z}_2$ skin effect. With the help of non-Bloch band theory, we unveil that the change of generalized Brillouin zone equation is the necessary condition of critical skin effect.Comment: 7+5 pages, 4+5 figure

FRACTAL DIMENSIONS OF A POROUS CONCRETE AND ITS EFFECT ON THE CONCRETE’S STRENGTH

All mechanical properties of a porous medium depend upon its fractal dimensions, however, how to measure the fractal dimensions is still an open issue. This paper adopts the two-scale fractal theory to calculate fast and effectively the fractal dimensions of a porous concrete. Of the concrete's properties that have been fascinating engineers and scientists, by far the most perplexing is the effects of its porosity and pore size on concrete's strength. Though there were many ad hoc empirical formulae for predicting the strength, much deviation arose for practical applications. Here a dimensionless model and the fractal theory are adopted to insight theoretically into the effects, and for the first time ever, some physically relative and mathematically reliable formulations are proposed. Additionally nano/micro particles’ size and distribution can also be used for theoretical prediction of the concrete’s strength, it shows that the boundary-induced force occurs when the particles tend to micro/nanoscales. The present theory sheds new light on the optimal design of various functional concretes

Monotherapy of acetylsalicylic acid or warfarin for prevention of ischemic stroke in low-risk atrial fibrillation: A Easter Asian population-based study

Background: This study aimed to investigate the effectiveness of monotherapy acetylsalicylic acid(ASA) and warfarin for stroke prevention in low-risk atrial fibrillation (AF) by using a population--based cohort study in Taiwan.Methods: A newly diagnosed low-risk AF patient cohort were identified by using National HealthInsurance Research Database (NHIRD) in Taiwan in 2008. The study cohort was observed witha follow-up of 2 years to examine the onset of ischemic stroke (IS) (to 2010). The longitudinal data wereanalyzed by using generalized estimation equations (GEE).Results: A total of 8,065 newly-diagnosed low-risk AF patients were identified in 2008. 7.4% wereprescribed with ASA and 4.6% were prescribed with warfarin. The GEE results showed that low-riskAF patients with hypertension who received warfarin were associated with a statistically significant58.4% reduction of IS risk (OR = 0.416, p = 0.024, 95% CI 0.194–0.891). Additionally, low-risk AFpatients with hyperlipidemia who received warfarin were associated with a 69.3% reduction of IS risk(OR = 0.307, p = 0.044, 95% CI 0.097–0.969).Conclusions: Warfarin is suggested to be prescribed in preventing IS for low-stroke-risk AF patientswith hypertension and hyperlipidemia