Microscopic Growth Mechanisms for Carbon Nanotubes

The uncatalyzed edge growth of carbon nanotubes was investigated by first-principles molecular dynamics simulations. At experimental temperatures the open end of single-walled nanotubes closed spontaneously into a graphitic dome, which may explain why these nanotubes do not grow in the absence of transition metal catalysts. On the other hand, chemical bonding between the edges of adjacent coaxial tubes ("lip-lip" interactions) trapped the end of a double-walled nanotube in a metastable energy minimum, thus preventing dome closure. These calculations show that this end geometry exhibits a high degree of chemical activity and easily accommodates incoming carbon fragments, supporting a model of growth by chemisorption from the vapor phase.     

Die „Uebelstänbe im Sächf. Forstdienst“ im Januarheft 1864 betreffend

Ohne Zusammenfassung     

Genetic technology and agricultural development

The genetic technologies being adopted in South Asia are significant factors in the agricultural development of the area. But, labeling them " miracle seeds," solely responsible for recent agricultural growth, is misleading. Certainly the introduction of new genetic technology has catalyzed South Asian agriculture and has instilled a new dynamism essential to economic development. Somewhat similar phenomena have, however, been observed in other parts of the world in other periods of history. The nature of these genetic technologies, how they are being applied, and their limits and potential have been explored above. Also, the effects of these varieties on the generation of employment, and the distribution of benefits accruing from them have been examined in preliminary fashion. Stemming from the preceding discussion, two areas of priority appear obvious. First, the close association of genetic technologies with irrigation suggests that irrigation should receive more attention than it has in the past. Large-scale public irrigation schemes are expensive and have tended to yield low rates of return. However, there appears to be room for marginal increases in, or improvements of, existing irrigation facilities. Second, even with a rapid spread of the practices associated with highyeild varieties, it may be too much to expect the farm sector to absorb the expected increases in the rural labor force. The generation of employment is a major problem in India as well as in most other developing countries. Hence, possibilities for expanding rural, nonfarm employment and controlling population growth should be sought vigorously.