Stratospheric ozone: Impact of human activity

Current knowledge of the chemistry of the stratosphere is reviewed using measurements from the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment to test the accuracy of our treatment of processes at mid-latitudes, and results from the Airborne Antarctic Ozone Experiment (AAOE) to examine our understanding of processes for the polar environment. It is shown that, except for some difficulties with N₂O₅ and possibly ClNO₃, gas phase models for nitrogen and chlorine species at 30°N in spring are in excellent agreement with the data from ATMOS. Heterogeneous processes may have an influence on the concentrations of NO₂, N₂O₅, HNO₃, and ClNO₃ for the lower stratosphere at 48°S in fall. Comparison of model and observed concentrations of O₃ indicate good agreement at 30°N, with less satisfactory results at 48°S. The discrepancy between the loss rate of O₃ observed over the course of the AAOE mission in 1987 and loss rates calculated using measured concentrations of ClO and BrO is found to be even larger than that reported by Anderson et al. (1989, J. geophys. Res. 94, 11480). There appear to be loss processes for removal of O₃ additional to the HOC1 mechanism proposed by Solomon et al. (1986, Nature 321, 755), the ClO-BrO scheme favored by McElroy et al. (1986, Nature 321, 759), and the ClO dimer mechanism introduced by Molina and Molina (1987, J. phys. Chem. 91, 433). There is little doubt that industrial halocarbons have a significant impact on stratospheric O₃. Controls on emissions more stringent than those defined by the Montreal Protocol will be required if the Antarctic Ozone Hole is not to persist as a permanent feature of the stratosphere.     

Farming and environmental degradation in Zambia: the human dimension

Farming and environmental degradation are inextricably linked through a complex of political, social, economic and physical forces. A connection is drawn between the initiation and maintenance of distinct farming systems (commercial, emergent and subsistence) by largely human influences, and the effect these farming systems have in turn on the environment. There are important implications for the environment through indirect effects on plant cover, cultivation methods and systems of bush fallowing. In many respects subsistence cultivation is probably the safest.A case study from Mkushi District, Central Province exemplifies the influence of external factors on environmental degradation in general, and soil erosion in particular. In the survey, traditional practices show fewer signs of soil erosion than commercial farming because of rational decisions taken by each group of farmers. The implication for conservation strategies is briefly reviewed.     

Inadequacies of the straits' passage regime in the LOS draft

Appraisers of recent sessions of the Law of the Sea Conference have directed their attention, sometimes at the expense of other critical issues, to the emerging regime to govern seabed mining. For one reason or another, a general Western consensus has emerged that the draft treaty's textual arrangements for traditional and innovative maritime and aerial passage are satisfactory. That complacent consensus may rest on perilously unrealistic assumptions.     

The Berkeley parasitic SETI Program

Parasitic programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. We describe a microprocessor-based automated SETI acquisition system which searches for and records spectra of narrowband signals in the IF band of an observatory receiver. Data taken with this system over 35 days at the Hat Creek Radio Observatory at 1612 MHz are discussed. Out of approximately 10⁵ spectra processed during this period, 4000 were identified by the system as containing narrowband signals and were recorded. Subsequent analysis indicates that over 3900 of these are due to local RF contamination. The remainder are undergoing further investigation.     

A simple contact–friction interface element with applications to buried culverts

A simple friction–contact interface element is introduced which simulates frictional slippage, separation, and re-bonding of two bodies initially mating at a common interface and subsequently deforming with an arbitrary static loading schedule. Constraint equations between initially mating node pairs and the general principle of virtual work are used to formulate the interface element for a finite element solution procedure. Some advantages of the interface element include; easy implementation intostandard finite element programs, direct determination of interface forces without round-off problems, and the generality afforded by the virtual work formulation to include other non-conservative models in the system. The application of the interface element to an idealized buried culvert problem illustrates that the model behaves properly. A second application, for a long-span culvert installation with incremental soil loading, demonstrates the importance of modelling slippage at the culvert–soil interface in order to conform with experimental observations.     

SEARCHING METHODS FOR RAPID GRID INTERPOLATION*

A widely used method for grid interpretation from a set of discrete sample points is based on the inverse distanceweighted model. This method requires the identification of k-nearest sample points for each grid point, probably the most time-consuming portion of the grid interpolation process. Three searching methods for identifying the k-nearest sample points are discussed and compared. Two of these methods were consistenty faster without sacrificing accuracy than the brute-force searching method, and one method was from one to over 90 times faster than the brute-force searching method.     

An evaluation of the use of halogen and water abundances in efforts to distinguish mineralized and barren intrusive rocks

Analysis of the chlorine, fluorine and water content of approximately 200 samples from a total of fourteen mineralized and ten barren intrusive rocks from the Caribbean and Central America indicates that abundances of these constituents fail to distinguish mineralized rocks from barren rocks. Variations in background abundances arise from the increase in halogen content of potassium-rich rocks and from the depletion of halogens in altered and porphyritic rocks. A particularly well developed potassium-fluorine covariance is observed in tin-bearing granites, but such a covariance cannot be used to distinguish intrusive rocks associated with porphyry copper mineralization.