The emergence and perils of polarization

We provide commentaries on the papers included in the Dynamics of Political Polarization Special Feature. Baldassarri reads the contribution of the papers in light of the theoretical distinction between ideological partisanship, which is generally rooted in sociodemographic and political cleavages, and affective partisanship, which is, instead, mostly fueled by emotional attachment and repulsion, rather than ideology and material interests. The latter, she argues, is likely to lead to a runaway process and threaten the pluralistic bases of contemporary democracy. Page sees the contribution of the many distinct models in the ensemble as potentially contributing more than the parts. Individual papers identify distinct causes of polarization as well as potential solutions. Viewed collectively, the papers suggest that the multiple causes of polarization may self-reinforce, which suggests that successful interventions would require a variety of efforts. Understanding how to construct such interventions may require larger models with greater realism.

Impact of Charging and Charging Rate on Thermal Runaway Behaviors of Lithium-Ion Cells

The present work carries out a series of thermal runaway experiments to explore the impact of charging and charging rate on the thermal runaway behaviors of lithium-ion cells, in which five charging rates (0C, 0.5C, 1C, 2C and 4C) and three initial states of charge (SOC), i.e. 25%, 50% and 75% are included. The thermal runaway process of 18650 lithium-ion cells induced by over-heating usually consists of seven stages, and is accompanied with high-temperature, fire and toxicity risks. The internal morphology of cells and the micro features of cell materials are seriously damaged after thermal runaway. Charging aggravates the thermal runaway behavior of cells, which is further exhibited as the earlier occurrence of safety vent opening, gas releasing and thermal runaway. Moreover, the severity deteriorates as the charging rate increases (the larger the charging rate, the earlier and more severe the thermal runway), which may be ascribed to the growth of cell SOC and the decline of cell stability under charging. This phenomenon is especially apparent for the cell with a high initial SOC where a more dramatic-rising α (the advancement ratio of critical times for thermal runaway due to charging) is observed.

Study on a horizontal axial flow pump during runaway process with bidirectional operating conditions

The ultra-low head pump stations often have bidirectional demand of water delivery, so there is a risk of runaway accident occurring in both conditions. To analyze the difference of the runaway process under forward runaway condition (FRC) and backward runaway condition (BRC), the whole flow system of a horizontal axial flow pump is considered. The Shear-Stress Transport (SST) k–ω model is adopted and the volume of fluid (VOF) model is applied to simulate the water surface in the reservoirs. Meanwhile, the torque balance equation is introduced to obtain the real time rotational speed, then the bidirectional runaway process of the pump with the same head is simulated. In addition, the vortex transport equation and swirl number are proposed to reveal the flow characteristics during the runaway process. The results show that the runaway process can be divided into five stages: the drop, braking, rising, convergence and runaway stages, according to the changing law of torque curve. In the rising stage, the pressure difference on the blade surface continues to increase, which contributes to the abnormal torque increase. In this stage, the flow hits the pressure surface (PS) at a faster speed enlarging the pressure on PS, and the flow separation takes place on the suction surface (SS) weakening the pressure on SS. During the convergence and runaway stage, the pulsation amplitude of torque and axial force under FRC is obviously larger than those under BRC. This is because the rotation frequency of the vortex rope is the same as main pressure fluctuation frequency in impeller under FRC, which enhances the pulsation amplitude. Whereas the vortices are broken due to the inhibitive effect from guide vanes under BRC.

Experimental Study on Thermal Runaway Process of 18650 Lithium-Ion Battery under Different Discharge Currents

Lithium-ion batteries (LIBs) subjected to external heat may be prone to failure and cause catastrophic safety issues. In this work, experiments were conducted to investigate the influence of discharge current on the thermal runaway process under thermal abuse. The calibrated external heat source (20 W) and discharge currents from 1 to 6 A were employed to match the thermal abuse conditions in an operational state. The results indicated that the key parameters during the failure process, such as the total mass loss, the onset temperatures of safety venting and thermal runaway, and the peak temperature, are ultimately determined by the capacity inside the battery, and the discharge current can hardly change it. However, discharge currents can produce extra energy to accelerate the thermal runaway process. Compared with the battery in an open circuit, the onset time of thermal runaway was reduced by 7.4% at 6 A discharge. To quantify the effect of discharge current, the total heat generation by discharge current was calculated. The results show that a heat generation of 1.6 kJ was produced when the battery was discharged at 6 A, which could heat the cell to 34 °C (neglect of heat loss). This study simulates the failure process of the LIB in the operational state, which is expected to help the safety application of LIB and improve the reliability of the battery management system.

Study on a Horizontal Axial Flow Pump during Runaway Process with Bidirectional Operating Conditions

The ultra-low head pump stations often have bidirectional demand of water delivery, so there is a risk of runaway accident occurring in both conditions. To analyze the difference of the runaway process under forward runaway condition (FRC) and backward runaway condition (BRC), the whole flow system of a horizontal axial flow pump is considered. The Shear-Stress Transport (SST) k-ω model is adopted and the volume of fluid (VOF) model is applied to simulate the water surface in the reservoirs. Meanwhile, the torque balance equation is introduced to obtain the real time rotational speed, then the bidirectional runaway process of the pump with the same head is simulated. Additionally, the vortex transport equation is proposed to compare the contribution of vortex stretching and vortex dilatation terms. According to the changing law of the impeller torque, the torque curve can be divided into five stages: the drop, braking, rising, convergence and runaway stages. By comparison, the rising peak value of torque under FRC is significantly higher than that under BRC in the rising stage. Simultaneously, through the short time Fourier transform (STFT) method, the amplitude of torque pulsation is obviously different between FRC and BRC. The analysis reveals that the flow impact on blade surface increases the pressure difference between the two sides of the blade in braking condition, which leads to the torque increase in the rising stage. Moreover, the pulsation amplitude of torque is mainly affected by the integrity of the vortex rope.

Runaway evolution from male-male competition

Understanding why and how elaborated traits evolve remains a fascination and a challenge. Darwin proposed both male-male competition and female mate choice as explanations for elaboration because such traits are often mediators of social interactions that govern access to mates. Although we have robust evolutionary quantitative genetic models for how mate choice can lead to runaway evolution, we lack an equivalent framework for understanding how male-male competition can drive extreme elaboration of traits. Here, we integrate the logic of optimality models into the quantitative genetic framework of interacting phenotypes to fill this gap. We assume that males modulate their aggression based on the relative size of a trait that signals willingness and ability to fight and identify conditions where the signal undergoes rapid and exponential evolution. Males receive fitness benefits from winning contests, but they may accrue fitness costs due to threats imposed by their opponent. This cost leads to a force of social selection that accelerates as the signaling trait is elaborated, which may cause runaway evolution of the signal. Even when a runaway is checked by natural selection, we find that signaling traits evolving by male-male competition can be elaborated well beyond their naturally selected optimum. Our model identifies simple conditions generating feedback between the behavioral and morphological traits mediating male-male competition, providing clear testable predictions. We conclude that, like the well-characterized case of female mate choice, male-male competition can provide a coevolving source of selection that can drive a runaway process resulting in evolution of elaborate traits.