Shock wave induced vaporization of porous solids

Strong shock waves generated by hypervelocity impact can induce vaporization in solid materials. To pursue knowledge of the chemical species in the shock-induced vapors, one needs to design experiments that will drive the system to such thermodynamic states that sufficient vapor can be generated for investigation. It is common to use porous media to reach high entropy, vaporized states in impact experiments. We extended calculations by Ahrens [J. Appl. Phys. 43, 2443 (1972)] and Ahrens and O'Keefe [The Moon 4, 214 (1972)] to higher distentions (up to five) and improved their method with a different impedance match calculation scheme and augmented their model with recent thermodynamic and Hugoniot data of metals, minerals, and polymers. Although we reconfirmed the competing effects reported in the previous studies: (1) increase of entropy production and (2) decrease of impedance match, when impacting materials with increasing distentions, our calculations did not exhibit optimal entropy-generating distention. For different materials, very different impact velocities are needed to initiate vaporization. For aluminum at distention (m)<2.2, a minimum impact velocity of 2.7 km/s is required using tungsten projectile. For ionic solids such as NaCl at distention <2.2, 2.5 km/s is needed. For carbonate and sulfate minerals, the minimum impact velocities are much lower, ranging from less than 1 to 1.5 km/s

Supplier search in industrial clusters: Sheffield metal working in the 1990s

Industrial clusters can be characterised by high levels of personal interaction between the owners/managers of firms. It has been argued that within industrial clusters community and firm tend to merge. One result of the notion of a cluster as a community is that it might be expected that personal interaction between members of the community will have an important influence on intra-cluster trading patterns. Whereas there appears to be a number of anecdotal stories of the impact of the 'personal' upon the 'economic' within clusters we do not know whether such relationships are uniquely part of cluster behaviour or whether they are found more widely within the industrial system. The paper reports the result of a new interview survey of seventy small metal working firms in the Sheffield metal working cluster in the UK. Although dealing with a traditional industrial sector the analysis is focused upon contemporary business patterns. It explores the ways in which owner/managers of small metal working firms search for new suppliers. In the empirical analysis the search process is conceptualised as being characterised by two stages: the identification of potential new suppliers and the selection of a specific new supplier. The research is in undertaken in two parts. It first measures the role of the personal networks of the owner/managers of small firms in the identification and selection of suppliers. Second, the research examines whether personal factors are more important in the identification and selection of within cluster suppliers than in the identification and selection of suppliers based outside the cluster. It is shown that, overall, personal networks are of major significance in the identification of suppliers and that information received from third parties are more important than direct contacts between the owner/manager and the potential supplier. However, in the selection decision, price and availability are dominant considerations and personal factors such as trust and reputation of only minor significance. It was not possible to identify a cluster effect in disaggregation of the data to separate out the relationships with cluster suppliers and relationships with suppliers based outside the cluster. There was no evidence that personal factors play a more important role in the establishment of within cluster links. In sum, personal networks are important in the identification of within cluster links but they are equally important in the establishment of links outside the cluster. This suggests that the importance of personal interaction within clusters has been overplayed.

Life-Long Physical Activity Involvement and the Risk of Ischemic Stroke in Southern China

A case-control study was conducted in southern China to investigate the relationship between life-long physical activity involvement and the risk of ischemic stroke. Information on life-long physical activity exposure and other lifestyle characteristics was obtained from 374 incident stroke patients and 464 hospital-based controls using a validated and reliable questionnaire. Logistic regression analyses were performed to assess the association between life-long physical activity involvement and the ischemic stroke risk. The control subjects reported more involvement in physical activity over the life course than the stroke patients (P < .001). The risk of ischemic stroke was inversely associated with life-long physical activity exposure, with adjusted odds ratio 0.39 (95% confidence interval 0.25 to 0.59) for participants who had always been involved relative to those who have never been much involved. The dose-response relationship was also significant (P < .001). Therefore, being active life long should be encouraged to prevent this major chronic disease

Cultural differences in indecisiveness: the role of naïve dialecticism

East Asians exhibit naïve dialecticism, a set of worldviews that tolerates contradictions. As influenced by naïve dialecticism, East Asians are more likely to hold and less likely to change ambivalent attitudes, compared with European North Americans. If East Asians have a heightened tendency to see both positive and negative aspects of an object or issue, but a lesser inclination to resolve these inconsistencies, East Asians (vs. European North Americans) may experience more difficulty in committing to an action, and thus be more indecisive. Consistent with this hypothesis, we found that East Asian Canadians scored higher on a measure of chronic indecisiveness than did European Canadians and South Asian Canadians, and that naïve dialecticism and need for cognition mediated the relationship between culture and indecisiveness. These results add to the extant literature on indecisiveness, demonstrating cultural variations in indecisiveness and an underlying cultural factor that is responsible for these cultural differences