香港華商會史研究計劃簡 介

In order to ensure a minimum strength for the low density fibrous tiles to be used in the thermal protection system of the Space Shuttle an NDE test that uses sonic velocity measurements to predict strength has been developed. The empirical correlation between strength and sonic velocity which is the basis of this test, is shown to be consistent with a previously developed micro-mechanical model. The model is reviewed and is shown to describe the fracture behavior of these fibrous materials regardless of their density or testing direction. Measurement of the density and sonic velocity in these materials allows Young’s modulus to be calculated and as low modulus materials tend to have low fracture toughness and strength, they can be eliminated by this test. Appropriate accept/reject criteria can be developed statistically from the strength or fracture toughness correlations but for use in design, other factors such as the size-dependence of strength, the stress fields encountered during flight, and the property variations within tiles should also be incorporated

Rebels without a conscience: the evolution of the rogue states narrative in US security policy

This article examines how the foundations of the ‘rogue states’ security narrative in the United States developed prior to the declaration of the George W. Bush administration’s ‘Global War on Terror’ and President Bush’s representation of Iraq, Iran and North Korea as an ‘axis of evil’. The article argues that the puzzle of how US post-Cold War foreign and defence policy came to be focused on ‘irrational’ — but militarily inferior — adversaries can be understood through analysing how actors within the US defence community discursively constructed discrete international crises as the trigger for a major shift in US threat scenarios. This is developed through an examination of two crucial episodes in the construction of post-Cold War US national security interests: the crisis in the Persian Gulf in 1990–1 and the North Korean nuclear crisis in 1993–4. The article suggests the importance of historicizing contests over the interpretation of international crises in order to both better understand the process through which a country’s national security interests are defined and to gain greater analytical purchase on how security narratives are reconstructed during processes of systemic change

Algal and aquatic plant carbon concentrating mechanisms in relation to environmental change

Carbon dioxide concentrating mechanisms (also known as inorganic carbon concentrating mechanisms; both abbreviated as CCMs) presumably evolved under conditions of low CO2 availability. However, the timing of their origin is unclear since there are no sound estimates from molecular clocks, and even if there were, there are no proxies for the functioning of CCMs. Accordingly, we cannot use previous episodes of high CO2 (e.g. the Palaeocene-Eocene Thermal Maximum) to indicate how organisms with CCMs responded. Present and predicted environmental change in terms of increased CO2 and temperature are leading to increased CO2 and HCO3- and decreased CO32- and pH in surface seawater, as well as decreasing the depth of the upper mixed layer and increasing the degree of isolation of this layer with respect to nutrient flux from deeper waters. The outcome of these forcing factors is to increase the availability of inorganic carbon, photosynthetic active radiation (PAR) and ultraviolet B radiation (UVB) to aquatic photolithotrophs and to decrease the supply of the nutrients (combined) nitrogen and phosphorus and of any non-aeolian iron. The influence of these variations on CCM expression has been examined to varying degrees as acclimation by extant organisms. Increased PAR increases CCM expression in terms of CO2 affinity, while increased UVB has a range of effects in the organisms examined; little relevant information is available on increased temperature. Decreased combined nitrogen supply generally increases CO2 affinity, decreased iron availability increases CO2 affinity, and decreased phosphorus supply has varying effects on the organisms examined. There are few data sets showing interactions among the observed changes, and even less information on genetic (adaptation) changes in response to the forcing factors. In freshwaters, changes in phytoplankton species composition may alter with environmental change with consequences for frequency of species with or without CCMs. The information available permits less predictive power as to the effect of the forcing factors on CCM expression than for their overall effects on growth. CCMs are currently not part of models as to how global environmental change has altered, and is likely to further alter, algal and aquatic plant primary productivity