Fully coordinated silica nanoclusters: (SiO2)(N) molecular rings

A new form of finite silica with edge-sharing SiO2 units connected in a ring is proposed. High-level density-functional calculations for (SiO2)(N), N = 4-14, show the rings to be energetically more stable than the corresponding (SiO2)(N) linear chains for N > 11. The rings display frequency modes in remarkable agreement with infrared bands measured on dehydrated silica surfaces indicating their potential as models of strained extended silica systems. Silica rings, if synthesized, may also be useful precursors for new bulk-silica polymorphs with tubular or porous morphologies

Nucleation of small silicon carbide dust clusters in AGB stars

Silicon carbide (SiC) grains are a major dust component in carbon-rich AGB stars. The formation pathways of these grains are, however, not fully understood.\ We calculate ground states and energetically low-lying structures of (SiC)$_n$, $n=1,16$ clusters by means of simulated annealing (SA) and Monte Carlo simulations of seed structures and subsequent quantum-mechanical calculations on the density functional level of theory. We derive the infrared (IR) spectra of these clusters and compare the IR signatures to observational and laboratory data.\ According to energetic considerations, we evaluate the viability of SiC cluster growth at several densities and temperatures, characterising various locations and evolutionary states in circumstellar envelopes.\ We discover new, energetically low-lying structures for Si$_{4}$C$_{4}$, Si$_{5}$C$_{5}$, Si$_{15}$C$_{15}$ and Si$_{16}$C$_{16}$, and new ground states for Si$_{10}$C$_{10}$ and Si$_{15}$C$_{15}$. The clusters with carbon-segregated substructures tend to be more stable by 4-9 eV than their bulk-like isomers with alternating Si-C bonds. However, we find ground states with cage ("bucky"-like) geometries for Si$_{12}$C$_{12}$ and Si$_{16}$C$_{16}$ and low-lying, stable cage structures for n $\ge$ 12. The latter findings indicate thus a regime of clusters sizes that differs from small clusters as well as from large-scale crystals. Thus, and owing to their stability and geometry, the latter clusters may mark a transition from a quantum-confined cluster regime to crystalline, solid bulk-material. The calculated vibrational IR spectra of the ground-state SiC clusters shows significant emission. They include the 10-13 $\mu$m wavelength range and the 11.3 $\mu$m feature inferred from laboratory measurements and observations, respectively, though the overall intensities are rather low.Comment: 16 pages, 25 figures, 3 tables, accepted for publication in Ap

Future of Wildlife Damage Control and the Cooperative Extension Service

The driving forces which determine the role of the Cooperative Extension Service in wildlife damage control are (1) the demand for information by the public, (2) the degree of support for programs at the national level, and (3) the level of professionalism exhibited by Cooperative Extension Agents and subject matter Specialists. Analysis of several trends suggests that the Cooperative Extension Service role in Wildlife Damage Control will increase in coming years. The movement of urban people into rural settings will create greater demands for wildlife damage control information. Likewise, the expansion of wildlife population into urban and suburban environments due to creation of new habitats will generate needs for new programs in cities. The emergence of the coyote as a prominent predator on livestock in the East will result in development of new Extension education programs to help farmers deal with coyotes. Each of these increases in conflicts between people and wildlife will be met with educational programs developed and presented by the Cooperative Extension Service. However, due to the increase in social concern over the rights of animals, the quality of extension programs and recommendations will increase. The high degree of professionalism characteristic of Extension workers today will continue and even expand in the future, as better trained people join the system, more research is completed on wildlife damage control problems, and better skills are developed in developing, presenting and evaluating extension programs

STATUS AND MANAGEMENT OF VOLE DAMAGE TO HORTICULTURAL PLANTINGS IN NORTH CAROLINA

A trapping study in 1979 indicated that voles (Microtus pinetorum and M. pinetorum) were distributed widely in North Carolina. In 1991, Extension Agents with the North Carolina Cooperative Extension Service were surveyed to determine the distribution, nature and severity of vole damage to horticultural plantings, home orchards, and other plantings. Data from the statewide trapping survey and the poll of agents coincided to indicate that voles, particularly pine voles, caused damage from the mountains to the coast. Existing, legal control methods were judged grossly inadequate by agents. Pursuant to the surveys, the North Carolina Pesticide Board and the North Carolina Wildlife Resources Commission were petitioned to approve changes in the North Carolina Administrative Code to reclassify voles as pests in horticultural plantings. The rule change, published on March 3, 1993, permitted use of non-restricted rodenticides to control voles. The product recommended was Rozol Parrafinized Pellets. Extension Agents enthusiastically welcomed the change. An extension publication for home horticulturalists on controlling vole damage is in preparation

Thrust-Impact Rock-Splitter

A rock splitting tool having elongate laterally expanding metal pressure bars or feathers and an axial sliding wedge or spreader for radially separating the feathers, the wedge being driven by the combined and superimposed forces of a hydraulic thrust servomotor and an impact hammer. The driving paths for transmitting forces to the wedge are coaxial and partially in series and partially in parallel