Supercritical carbon dioxide as a new working medium for pneumatic launch: A theoretical study

Compared with the conventionally gaseous or liquid working media, the specific internal energy of supercritical carbon dioxide (SCD) is higher at the same temperature and pressure, and the critical temperature of carbon dioxide is close to room temperature, making SCD a potential new working medium for pneumatic launch. To analyze the feasibility of this conception, an analytical model of a pneumatic catapult is established on basis of the conservations of mass and energy. The model consists of a high-pressure chamber and a low-pressure chamber connected by multiple valves, and there is a movable piston in the low-pressure chamber that can push an aircraft to accelerate. The effects of the launch readiness state of SCD in the high-pressure chamber, the initial volume of the low-pressure chamber and the valve control on the movement of the aircraft are analyzed. It is found that there is a restrictive relation between the temperature and pressure of the launch readiness state of SCD, i.e., there is a maximum allowable launch readiness pressure when the launch readiness temperature is fixed. If this restrictive relation is not satisfied, the working medium in the low-pressure chamber will drop to its triple point within a few milliseconds, leading to a launch failure. Owing to this restrictive relation, there is an optimal launch readiness state of SCD with the highest working capacity for any allowable launch readiness temperature. The pressure of the low-pressure chamber will decrease significantly as the initial volume increases, leading to a decreased acceleration of the aircraft. The ac-celeration can be controlled below a critical value by a designed sequential blasting technique of multiple valves. The calculated results show that a 500 kg aircraft can be accelerated from 0 to 58 m/s in 0.9 s with 36 kg of carbon dioxide. This research provides a new technique for the controllable cold launch of an aircraft.     

Peacekeeping and civil–military relations in Uruguay

ABSTRACT

There have been over 90,000 UN peacekeepers deployed around the world to 78 peacekeeping operations (PKOs) in over 125 countries since 1948. Some scholars have made the case that these missions have had a positive impact on the relationship between the military and the civilians they work for. However, other scholars have identified a negative impact on civil military relations (CMR). This paper contributes to this debate by investigating how peacekeeping has impacted civil-military relations in Latin America's most prolific contributor to peacekeeping: Uruguay. This paper finds that PKOs in Uruguay have facilitated post-transitions attempts by civilians to build first-generation control, but not second-generation control. Further, PKOs have marginally improved military effectiveness, but we find that they do not improve societal trust in the armed forces.     

Tarnishing victory? Contested histories & civil–military discord in the U.S. Navy, 1919–24

ABSTRACT

As the First World War came to an end, the U.S. Navy's leadership engaged in a bitter fight over the “lessons” of the war. Admiral William S. Sims and Secretary of the Navy Josephus Daniels fought against each other's irreconcilable positions. Sims argued that the Navy Department's inexpert civilian secretary had hamstrung mobilisation, impeded the anti-submarine campaign, and ostracised capable officers in favour of friends upon whom he bestowed medals. Daniels countered that his administration had masterfully responded to the crisis of war. The Navy's record, Daniels insisted, could best be summarised as “a great job greatly done.” Only disloyal nit-pickers could find fault in its accomplishments. The Sims-Daniels controversy raged in congressional hearings, the press, and in partisan histories written by the protagonists. The heart of the dispute and its uncertain resolution rested in radically different understandings of American civil–military relations, naval heroism, and the determinants of victory.     

Understanding women at war: a mixed-methods exploration of leadership in non-state armed groups

ABSTRACT

Recent efforts aimed at understanding women’s contributions to nonstate armed groups have produced large-scale data sets on female combatants (Wood and Thomas 2017) and more limited data on women’s roles as supporters and leaders in armed groups (Henshaw 2016; 2017, Loken 2018). The present study aims to build on this literature by providing new data on the scope of women’s leadership in insurgent groups. While existing quantitative literature has focused mostly on the experience of female combatants, we argue that the presence of women in leadership roles is crucial to understanding how gender might influence the outcomes of insurgency. We introduce new data on over 200 insurgent groups active since World War II. While our analysis confirms earlier small-sample work demonstrating women’s presence in leadership roles, a qualitative analysis reveals that leadership is often gendered–revealing patterns of tokenization and tracking women to low-prestige leadership roles. At the same time, our findings challenge past research on jihadist organizations, showing limited expansion in the authority of women.     

Anarchy’s anatomy: Two-tiered security systems and Libya’s civil wars

ABSTRACT

No issue deserves more scrutiny than the mechanisms whereby popular unrest unleashes civil wars. We argue that one institution – two-tiered security systems – is particularly pernicious in terms of the accompanying civil war risk. These systems’ defining characteristic is the juxtaposition of small communally stacked units that protect regimes from internal adversaries with larger regular armed forces that deter external opponents. These systems aggravate civil war risks because stacked security units lack the size to repress widespread dissent, but inhibit rapid regime change through coup d’état. Regular militaries, meanwhile, fracture when ordered to employ force against populations from which they were recruited.