COVID-19 Pandemic: How Effective Are Preventive Control Measures and Is a Complete Lockdown Justified? A Comparison of Countries and States

For fighting the COVID-19 pandemic, countries used control measures of different severity, from “relaxed” to lockdown. Drastic lockdown measures are considered more effective but also have a negative impact on the economy. When comparing the financial value of lost lives to the losses of an economic disaster, the better option seems to be lockdown measures. We developed a new parameter, the effectiveness of control measures, calculated from the 2nd time derivative of daily case data, for 92 countries, states and provinces. We compared this parameter, and also the mortality during and after the effective phase, for countries with and without lockdowns measures by means of the Mann–Whitney test. We did not find any statistically significant difference in the effectiveness between countries with and without lockdowns (p > 0.76). There was also no significant difference in mortality during the effective phase (p > 0.1); however, a significant difference after the effective phase, with higher mortality for lockdown countries, was identified. The effectiveness correlated well with a parameter derived from the reproductive number (R2 = 0.9480). The average duration of the effective phase was 17.3 ± 10.5 days. The results indicated that lockdown measures are not necessarily superior to relaxed measures, which in turn are not necessarily a recipe for failure. Relaxed measures are, however, more economy-friendly.

Synergistic regulation mechanism of selectin and integrin on leukocyte adhesion under shear flow

In the process of inflammation, the hydrodynamic process of circulating leukocyte recruitment to the inflammatory site requires the rolling adhesion of leukocytes in blood vessels mediated by selectin and integrin molecules. Although a number of experiments have demonstrated that cooperative effects exist between selectins and integrins in leukocyte rolling adhesion under shear flow, the mechanisms underlying how the mechanics of selectins and integrins synergistically may govern the dynamics of cell rolling is not yet fully resolved. Here we present a mechanical model on selectin- and integrin- jointly mediated rolling adhesion of leukocyte in shear flow, by considering two pairs' binding/unbinding events as Markov processes and describing kinetics of leukocyte by the approach of continuum mechanics. Through examining the dynamics of leukocyte rolling as a function of relative fraction of selectin and integrin pairs, we show that, during recruitment, the elongation of intermittent weak selectin bonds consuming the kinetic energy of rolling leukocyte decelerates the rolling speed and enables the integrin pairs to form strong bonds, therefore achieving the arrestment of leukocyte (firm adhesion). The coexistence of selectins and integrins may also be required for effective phase transition from firm adhesion to rolling adhesion, due to dynamic competition in pairs' formation and elongation. These results are verified by the relevant Monte Carlo simulations and related to reported experimental observations.

Cooperative escape in ants and robots

The solution of complex problems by the collective action of simple agents in both biologically evolved and synthetically engineered systems involves cooperative action. Understanding the resulting emergent solutions requires integrating across the organismal behaviors of many individuals. Here we investigate an ecologically relevant collective task in black carpenter ants Camponotus pennsylvanicus: escape from a soft, erodible confining corral. Individual ants show a transition from individual exploratory excavation at random locations to spatially localized collective exploitative excavation and escape from the corral. A minimal continuum theory that coarse-grains over individual actions and considers their integrated influence on the environment leads to the emergence of an effective phase space of behaviors in terms of excavation strength and cooperation intensity. To test the theory over the range of predicted behaviors, we used custom-built robots (RAnts) that respond to stimuli and show the emergence (and failure) of cooperative excavation and escape. Overall, our approach shows how the cooperative completion of tasks can arise from relatively simple rules that involve the interaction of simple agents with a dynamically changing environment that serves as an enabler and modulator of behavior.

Phase management in single-crystalline vanadium dioxide beams

A systematic study of various metal-insulator transition (MIT) associated phases of VO2, including metallic R phase and insulating phases (T, M1, M2), is required to uncover the physics of MIT and trigger their promising applications. Here, through an oxide inhibitor-assisted stoichiometry engineering, we show that all the insulating phases can be selectively stabilized in single-crystalline VO2 beams at room temperature. The stoichiometry engineering strategy also provides precise spatial control of the phase configurations in as-grown VO2 beams at the submicron-scale, introducing a fresh concept of phase transition route devices. For instance, the combination of different phase transition routes at the two sides of VO2 beams gives birth to a family of single-crystalline VO2 actuators with highly improved performance and functional diversity. This work provides a substantial understanding of the stoichiometry-temperature phase diagram and a stoichiometry engineering strategy for the effective phase management of VO2.

Gap-Size-Dependent Effective Phase Transition in Metasurfaces of Closed-Ring Resonators

We theoretically investigate a metal-to-insulator transition in artificial two-dimensional (2D) crystals (i.e., metasurfaces) of tightly coupled closed-ring resonators. Strong interaction between unit resonators in the metasurfaces yields the effective permittivity highly dependent on the lattice spacing of unit resonators. Through our rigorous theory, we provide a closed form of effective permittivity of the metasurface and reveal that the permittivity possesses a Lorentzian-type resonant behavior, implying that the transition of the effective permittivity can arise when the lattice spacing passes a critical value.

Prion-like Conformational Editing of SMN2 Proteins Rescues Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) causes the loss of motor neurons and progressive muscle weakness. In 95% of patients with SMA, both alleles of the survival motor neuron 1 (SMN1­) gene are deleted or the gene contains missense mutations. A nearly identical copy of SMN1, SMN2, is normally expressed but is unable to compensate for the loss of SMN1 due to the deletion of exon 7. Here, we demonstrated that conformational editing of the SMN2 protein triggers effective phase separation of SMN2 proteins and rescues SMA. We found that SMN1 contains a prion-like LC domain at exons 6-7, which drives liquid-liquid phase separation (LLPS) and further discovered an LLPS activator of gems, baicalein. Using baicalein, we reinvented SMN2 proteins into a competent prion-like conformation to restore the prion-like functions of SMN1 and effectively rescue SMA mice. Our study suggests that the impaired prion-like activity of SMN1 is the root cause of SMA and provides a drug candidate for SMA and phase separation-deficient diseases.