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ObjectivesInforming research participants of the results of studies in which they took part is viewed as an ethical imperative. However, there is little guidance in the literature about how to do this. The Fluoxetine Or Control Under Supervision trial randomised 3127 patients with a recent acute stroke to 6 months of fluoxetine or placebo and was published in the Lancet on 5 December 2018. The trial team decided to inform the participants of the results at exactly the same time as the Lancet publication, and also whether they had been allocated fluoxetine or placebo. In this report, we describe how we informed participants of the results.DesignIn the 6-month and 12-month follow-up questionnaires, we invited participants to provide an email address if they wished to be informed of the results of the trial. We re-opened our trial telephone helpline between 5 December 2018 and 31 March 2019.SettingUK stroke services.Participants3127 participants were randomised. 2847 returned 6-month follow-up forms and 2703 returned 12-month follow-up forms; the remaining participants had died (380), withdrawn consent or did not respond.ResultsOf those returning follow-up questionnaires, a total of 1845 email addresses were provided and a further 50 people requested results to be sent by post. Results were sent to all email and postal addresses provided; 309 emails were returned unrecognised. Seventeen people replied, of whom three called the helpline and the rest responded by email.ConclusionIt is feasible to disseminate results of large trials to research participants, though only around 60% of those randomised wanted to receive the results. The system we developed was efficient and required very little resource, and could be replicated by trialists in the future.Trial registration numberISRCTN83290762; Post-results.

Biomass energy accounts for more than 90% of the total rural energy supplies in developing countries. The combustion of domestic biofuels results in the emission of trace gases such as CO2, CO, NO and CH4 and aerosols. Such gases have a significant influence on climate and biogeochemical cycles. Trace gas emissions in this study were estimated based on the amount of domestic biofuel used by rural households across southern African countries. This study found that South Africa contributes the most trace gases to the regional budget (9.12 Tg C a−1 of CO2, 0.89 Tg C a−1 of CO, 10.77 Gg N a−1 of NO and 30.25 Gg C a−1 of CH4) and Botswana the least (0.25 Tg a−1 of CO2, 0.02 Tg a−1 of CO, 0.29 Gg a−1 of NO and 0.83 Gg a−1 of CH4). Fuelwood is the dominant fuel type used in all southern African countries and contributes to high emissions of trace gases. Annual CO2, CO, NO and CH4 emissions produced in Southern Africa are 23.0 Tg C, 2.2 Tg C, 29.4 Gg N and 81.4 Gg C, respectively.

This observational study used field tests to investigate the association between physiological parameters and rowing performance in athletes during ergometer and on-water Swiss national competitions. 25 Participants between 15 and 35 years who compete at national level were recruited among different clubs. We assessed anthropometric parameters such as weight, height, aerobic capacity during an incremental test on a rowing ergometer, anaerobic capacity during an on rowing ergometer Wingate test and lower limb strength and power during countermovement- and squat jumps. We took as performance measurements the results from two on-ergometer and two on-water rowing races. 25 rowers (age 17.4 ± 2.4 years), 6 women and 19 men participated in this study. We found very high to moderate correlations between on-ergometer performance and aerobic capacity (r = 0.91), anaerobic capacity (r = 0.78) and lower limb strength and power (r = 0.83; r = 0.73) as well as moderate correlations between on-water performance and aerobic capacity (r = 0.63), anaerobic capacity (r = 0.60) and lower limb strength and power (r = 0.54; r = 0.64). This study present descriptive performance reference values of elite Swiss rowers. Field tests are indicators of specific performance but more extensive studies would confirm the associations, notably according to the competition type. Once confirmed, the different strength of correlations between physiological parameters and rowing performances might be helpful in the near future to better adapt rowers’ training preparation and athletes’ selection for an elite team.

Direct and indirect decomposition of retained austenite during tempering are investigated in a 0.2C wt% steel with a carbide-free bainitic microstructure. The decomposition products of both mechanisms are quantified using X-ray diffraction and quantitative metallography; using dilatometry data to support interpretation. Two nearly identical steels are compared, with and without vanadium. The influence of vanadium on both direct and indirect decomposition of retained austenite is discussed, along with the effect of vanadium on hardness changes during tempering.

Monitoring of surface ozone over southern Africa has shown that ambient concentrations often exceed a threshold of 40 ppb at which damage to vegetation by ozone could be expected. The Cross Border Air Pollution Assessment Project (CAPIA) was therefore established to assess the potential impacts of ozone on maize, a staple food crop, in five southern African countries. Measured surface ozone data are scare in the region so it was necessary to complement the monitoring with regional-scale photochemical modelling to achieve the objective. The Pennsylvania State and NCAR Mesoscale Model (MM5) is used to produce gridded meteorological data for 5 days in each month of the maize growing season, October to April, as input to the photochemical model, CAMx. Gridded anthropogenic emissions from industry, transport and domestic burning and gridded biogenic emissions from soils and vegetation are input to CAMx. The model estimations indicate large areas on the sub-continent where surface ozone concentrations exceed 40 ppb for up to 10 h per day. Maximum concentrations may exceed 80 ppb, particularly in the winter when mean ozone concentrations are higher. The areas where the 40 ppb threshold is exceeded coincide with maize growing areas in South Africa and Zimbabwe. It appears that neither anthropogenic emissions nor biogenic emissions are dominant in the production of surface ozone over southern Africa. Rather the formation of surface ozone over the region is attributed to the combined contribution of precursors from anthropogenic and biogenic origin. 2005 Elsevier Ltd. All rights reserved.

Surface ozone concentrations in southern Africa exceed air quality guidelines set to protect agricultural crops. This paper addresses a knowledge gap by performing a preliminary assessment of potential ozone impacts on vegetation in southern African. Maize (Zea mays L.) is the receptor of interest in the main maize producing countries, i.e. South Africa, Zambia and Zimbabwe. Surface ozone concentrations are estimated for the growing season (October to April) using photochemical modelling. Hourly mean modelled ozone concentrations ranged between 19.7 and 31.2 ppb, while maximums range between 28.9 and 61.9 ppb, and are near 30 ppb over South Africa and Zambia, while in Zimbabwe, they exceed 40 ppb and translate into monthly AOT40 values of over 3,000 ppb h in five of the seven months of the growing season. This study suggests that surface ozone may pose a threat to agricultural production in southern African, particularly in Zimbabwe.

Nitrogen (N) cycling was analyzed in the Kalahari region of southern Africa, where a strong precipitation gradient (from 978 to 230 mm mean annual precipitation) is the main variable affecting vegetation. The region is underlain by a homogeneous soil substrate, the Kalahari sands, and provides the opportunity to analyze climate effects on nutrient cycling. Soil and plant N pools, 15N natural abundance (δ15N), and soil NO emissions were measured to indicate patterns of N cycling along a precipitation gradient. The importance of biogenic N2 fixation associated with vascular plants was estimated with foliar δ15N and the basal area of leguminous plants. Soil and plant N was more 15N enriched in arid than in humid areas, and the relation was steeper in samples collected during wet than during dry years. This indicates a strong effect of annual precipitation variability on N cycling. Soil organic carbon and C/N decreased with aridity, and soil N was influenced by plant functional types. Biogenic N2 fixation associated with vascular plants was more important in humid areas. Nitrogen fixation associated with trees and shrubs was almost absent in arid areas, even though Mimosoideae species dominate. Soil NO emissions increased with temperature and moisture and were therefore estimated to be lower in drier areas. The isotopic pattern observed in the Kalahari (15N enrichment with aridity) agrees with the lower soil organic matter, soil C/N, and N2 fixation found in arid areas. However, the estimated NO emissions would cause an opposite pattern in δ15N, suggesting that other processes, such as internal recycling and ammonia volatilization, may also affect isotopic signatures. This study indicates that spatial, and mainly temporal, variability of precipitation play a key role on N cycling and isotopic signatures in the soil–plant system.

We examined relationships between vegetation and soil nutrients along rainfall and land use gradients in the Kalahari. Soil organic carbon (SOC) was significantly lower where reduced rainfall and grazing lowered litter inputs to the soil. Soil organic nitrogen (SON) was significantly lower at the driest site and was higher than expected at two grazed sites. Ammonium levels at Mongu (wettest) were significantly higher, while nitrate was lower than expected everywhere. Site-averaged concentrations showed no significant differences in SOC and SON beneath plant canopies, but woody plant canopies alone showed elevated SOC at three sites and SON at one site.

Biogenic volatile organic carbon (BVOC) emissions are an important component of the global BVOC budget, contributing more than 90%. Emissions vary with species and vegetation type; therefore to produce accurate global budgets data is required from different vegetation types. This study investigates BVOC emissions from savannas, Kalahari woodlands, Kalahari open shrublands and Mopane woodlands in southern Africa. BVOC emission samples from individual species were collected using leaf cuvettes and the BVOC concentrations were determined by GC-FID/ MS. Ten of the 14 woodland species measured were high isoprene emitters, while two showed high monoterpene emission capacities. Landscape average isoprene emission capacities were estimated to be as high as 9, 8 and 1 mg Cm � 2 h � 1 for savannas, woodlands and shrub lands, respectively. The monoterpene emission capacity for Mopane woodlands were estimated at almost 3 mg C m � 2 h � 1 , while for other landscapes it varied between 0.04 and 3 mg Cm � 2 h � 1 . Isoprene and monoterpene emissions at a savanna site in South Africa showed a seasonal variation, which is more pronounced for isoprene. During the winter (June–September) estimated emissions were o10 mg C m � 2 d � 1 , with peak emissions (ranging between 20 and 80 mg C m � 2 d � 1 ) occurring during the summer months (December–March) when foliar density peaked. The total BVOC emission from southern African (south of the Equator) savannas was estimated to be in the range of 18–74 Tg C yr � 1 . r 2002 Elsevier Science Ltd. All rights reserved.

Aerosol samples were collected at Nylsvley Natural Reserve in northeastern South Africa at the beginning of the dry season, when large-scale fires were absent. Aerosol was collected on quartz fiber filters with open face stack filters in an inlet with an upper cutoff mass median diameter of 30 μm. The samples were analyzed for soluble ions (Cl - , NO - 3 , SO 2- 4 , oxalatc, NH + 4 , Na + , K + , Ca 2+ , Mg 2+ ), trace metals and crustal elements (Fe, Mn, Ca, Mg, Pb, Cu, Ag, Cd), black carbon (BC), total carbon (TC); and in selected samples for aerosol humidity, for mono- and dicarboxylic acids and other polar organic components, and for cellulose as a tracer for plant debris. Aerosol mass balances for the individual samples were constructed from the sum of following groups: Humidity (determined as weight loss at 100°C with a microthermobalance), ammonium sulfate, Cl and NO 3 - , organic material, BC, and soil dust. On the average, the fit between the sum of the determined groups of components and the gravimetrically determined mass was within 6%, whereas deviations ranged for individual samples from -12 to +27% relative to the gravimetrically determined mass. The main component in aerosol was soil dust (36%), followed by organic material (28%), and ammonium sulfate (27%). Humidity was 6%, BC was 2%, and Cl - and NO 3 were 1% of aerosol mass. The low BC/TC ratio of 0.09 indicated little influence from combustion sources. The diurnal trend of the BC/TC ratio of 0.06 during day and 0.14 during night indicated a daytime source for organic components with no BC associated. As there were no industrial or other anthropogenic sources evident, the daytime source of organic components is assumed to be gas-particle conversion from biogenic emissions. Plant debris and organic acids were the major analytically accessible groups; however, together they form only 7.2% of the carbonaceous material. With 0.4% other polar organics and 5.7% BC in this group, 86.7% of the carbonaceous material remains unidentified.

Methane (CH4) fluxes were measured over a 2-year period at subtropical savanna and floodplain sites located in South Africa. No significant differences were detected in fluxes from the nutrient-rich and nutrient-poor savannas. Savannas were not always sinks and showed some CH4 emissions during the wet, summer season with fluxes in the range of −1.6 to 1.68 mg m−2 d−1. Soil temperature did not have a significant effect on the flux, while CH4 consumption decreased and emissions increased with an increase in soil moisture between 5% and 50% water-filled-pore-space (WFPS). Understanding the factors which control the production and emission of CH4 in aerobic environments is extremely important for predicting net emissions from a region. Dry floodplain soil fluxes were near zero and did not differ significantly from savanna fluxes. During a flood, saturated sites emitted CH4 at an average rate of 69.4 mg m−2 d−1. Flooded areas with a water depth of 0.3 - 0.4 m emitted CH4 from the water surface at rates between 0.48 and 466.3 mg m−2 d−1 with the highest emission occurring during summer. Emission rates were exponentially related to sediment temperature, which had a greater influence on the emission rate than the flood regime. The length of the dry period preceding the flood and the extent of a flood did not have a significant effect on CH4 fluxes from saturated and flooded sites. Emission rates were highest when the water level was between 0.1 m below the soil surface and 0.4 m above the soil surface, with emission rates declining to near zero as the water became deeper than 0.4 m. Savannas were estimated to consume an average of 0.04 g CH4 m−2 d−1, with southern African savannas consuming 0.23 Tg CH4 yr−1. Saturated and flooded sites were estimated to produce 25.3 and 57.2 g CH4 m−2 d−1, respectively. Southern African floodplains are estimated to produce between 0.2 and 10 Tg CH4 yr−1(excluding the effects of vegetation-mediated emissions) and therefore produce more CH4 than the savannas consume.

Secondary ion mass spectrometry (SIMS) techniques have been used to study the variation of C isotope ratio and N abundance within selected diamonds in relation to their crystal growth zones. The growth zones are seen in cathodoluminescence (CL), and include both octahedral and cuboid zones within typical diamonds of external octahedral morphology. Compositions were determined by use of a primary 133Cs+ ion beam and measurement of 12C−, 13C, and 12C14N− secondary ions at high mass resolution on a Cameca ims-4f ion microprobe at Edinburgh University. In each of the diamonds, different growth zones have marked differences in N abundance, which are as great as 0–1400 ppm within one diamond. Changes of several hundred ppm N are common across both octahedral and cuboid growth zones, and appear sharp and abrupt at the boundaries of the growth zones. In general for the common blue CL, luminescence increases with N abundance. The changes in N abundance across fine scale (∼100 µm) growth zones show that the total N contents determined by IR spectroscopy may show great variations of abundance. In contrast, within detection limits, δ13C appears constant across many growth zone boundaries. Thus the factors controlling uptake of N from the fluid/melt reservoir in which natural diamonds grow often do not influence δ13C. No evidence of progressive variation or fractionation of C isotopes during growth was found. Some original variation in C isotope composition may have been eliminated by diffusion of C atoms subsequent to growth, because of the storage of natural diamonds over millions of years in the Earth's mantle at temperatures of 950–1250°C. Such atomic mobility does not homogenize N distribution because of the proven tendency of N to form aggregates of atoms. A survey of experimental estimates of single atom (C) diffusion parameters, suggests that diffusion distances of ∼100 µm are likely at high temperatures (∼1100°C) over long time periods (∼1.0 Ga). Therefore, with refinement of the diffusion parameters and measurements, the extent of C isotope homogenization in natural diamonds, as well as N aggregation state, might provide quantitative evidence of their time-temperature history under mantle conditions.

NO fluxes from soils of a periodically flooded tropical savanna in southern Africa were investigated and modeled. In the laboratory, NO production rates, NO consumption rate constants, NO mixing ratios, relationships between NO emissions and soil temperature and moisture were determined for nutrient-poor, nutrient-rich savanna soils and a floodplain soil. The NO production rate and consumption rate constants of the floodplain soil (1.96 ng N s−1 per kilogram of soil and 2.04×10−5 m3 s−1 per kilogram of soil, respectively) were significantly higher than those of the savanna soils (average of 1.28 ng N s−1 per kilogram of soil and 1.47×10−5 m3 s−1 per kilogram of soil, respectively), but there were no significant difference between the nutrient-rich and nutrient-poor soils. NO flux rates increased exponentially with soil temperature. NO flux rates increased with soil moisture reaching a maximum near the field capacity (7.5–10% and 31.2% gravimetric water content for savanna and floodplain soils, respectively), after which the NO flux rate declined. These laboratory data were used in a model to estimate field NO flux rates, which were compared with actual field NO emission measurements. The NO model was modified to incorporate NO “pulsing” after the first rains of the season. Correlation between the modeled and field NO fluxes from the nutrient-poor savanna, nutrient-rich savanna, and the floodplain soils showed r2 values of 0.91, 0.82, and 0.74, respectively. The NO model was linked with a soil moisture and temperature model to predict annual NO emission estimates from savannas. Annual NO flux from the nutrient-poor and nutrient-rich savannas was estimated to be 0.16×10−3 and 0.14×10−3 kg N m−2 yr−1, respectively, which agree well with estimates from other savanna studies.

Two xenoliths of garnet harzburgite from the Finsch kimberlite, South Africa, have been found to contain diamond. One of the xenoliths has mineral compositions typical of low-T coarse textured garned peridotites, whereas minerals in the other are similar but not identical to most peridotite-suite minerals included in diamonds, especially in the low-CaO content of garnet. Geothermobarometric calculations show both xenoliths equilibrated at temperatures above 1,100°C and pressures>55 kbar, which is near the low-pressure end of the range of equilibration conditions for diamond-free garnet lherzolites and garnet harzburgites from Finsch. The chemistries of the minerals in the two rocks are distinctly different to most of the mineral inclusions in Finsch diamonds. This, as well as the different δ13C compositions between xenolith diamonds (-2.8 to-4.6‰) and diamonds in the kimberlite (generally

Garnet inclusions of the eclogite paragenesis from large single diamonds (1.8 to 4.2 carats) from the 120 Ma Finsch kimberlite have Nd model ages ranging from 1443 to 2408 Ma. Ages of 1443 ± 166 and 1657 ± 77 Ma in two samples with 87 Sr 86 Sr = 0.7042 may represent the age of diamond formation and are within error of a 1580 ± 50 Ma Sm-Nd isochron age on clinopyroxene and garnet reported by Richardson et al. (1990). Older model ages in three other samples (1824, 2183, and 2408 Ma) correspond with unsupported radiogenic Sr ( 87 Sr 86 Sr = 0.7095 to 0.7158 ) and anomalously high MnO (0.7 to 1.2 wt%.) suggestive of multistage evolution. Carbon isotopic compositions of the diamonds range from −3.6 to −7.7%., and do not correlate with isotopic or chemical features of the inclusions. Compared to world-wide compositional ranges of most eclogite paragenesis garnet inclusions in diamonds, four of five analyzed here are anomalously enriched in Fe and Mn, possibly a characteristic feature of the Finsch eclogitic diamond paragenesis suite. A large diamond with a websterite inclusion assemblage (clinopyroxene, orthopyroxene, garnet) from the Kimberley Pool (85 Ma emplacement age) has clinopyroxene with a Nd model age of 2111 ± 120 Ma. In contrast to the high Sm/Nd and radiogenic Nd of the eclogite garnets, the websterite cpx has low Sm/Nd and unradiogenic Nd more akin to that in garnet of harzburgite association diamonds from the Finsch kimberlite. However, neither the eclogite nor the websterite group diamonds can be related to the harzburgite suite. Analysis of inclusions from single diamonds eliminates the problems inherent in compositing possibly unrelated inclusions from large numbers of stones, but the large diamond size required to yield large inclusions may represent only a specific and possibly rare component of the general diamond population. The samples analyzed here may have been derived ultimately from subducted oceanic crust.

In the past decade, the isotopic compositions of C in > 600 inclusion-bearing diamonds have been determined. Such analyses have revealed the following isotopic characteristics: (1) peridotitic diamonds, which typically contain garnet, chromite, olivine and/or orthopyroxene inclusions with refractory compositions (high Mg, Cr), have δ 13 C values predominantly between −10 and −1‰, with a sharp peak in the distribution near −5‰; (2) eclogitic diamonds, which commonly contain inclusions of omphacitic clinopyroxene, Cr-poor pyrope, and/or eclogitic accessory minerals such as rutile, kyanite, coesite or sanidine, have δ 13 C values between −34 and +3‰, with a smaller peak near −5‰; (3) the isotopic compositions obtained for suites of diamonds from individual occurrences are, in general, unique and do not resemble the range and distribution obtained by amalgamating the diamond isotope data from a number of localities; (4) isotopic zoning patterns and heterogeneities are found in some diamonds; cores of coated diamonds tend to be depleted in 13 C relative to the rims, and within single octahedral diamonds δ 13 C variations of nearly 6‰ have been reported. Because expected C isotope fractionations at mantle temperatures are small, attempts to model the full range of diamond isotope values through fractionating a homogeneous mantle C source have been unsuccessful. Nevertheless, fractionation is probably responsible for some of the observed variation in δ 13 C values. Two other models have also been proposed to account for the diamond characteristics outlined above. The “primordial model” suggests that the range and distribution of C isotope compositions are inherited from primordial C in the mantle which has an inhomogeneous isotopic composition, such as that found in meteorites. The “subduction model” suggests that subducted, crustal C is the source of C in diamonds, as organic and inorganic C compounds in the crust exhibit a range of δ 13 C values similar to that observed in diamonds. This paper reviews the C isotope characteristics of diamonds and compares the models which have been proposed to explain the origins of these characteristics.

[1] Improved vegetation distribution and emission data for Africa south of the equator were developed for the Southern African Regional Science Initiative (SAFARI 2000) and were combined with biogenic volatile organic compound (BVOC) emission measurements to estimate BVOC emissions for the southern African region. The BVOCs are estimated to total 80 Tg C yr−1 for the region, with isoprene and monoterpenes contributing 56 and 7 Tg C yr−1, respectively. The large uncertainties, particularly in terms of basal emission capacity assignment, associated with these outputs are discussed. Woodlands are predicted to be the dominant vegetation type, covering 23% of southern Africa, and are the largest annual source of isoprene (20 Tg C), monoterpenes (3 Tg C), and other VOCs (4 Tg C). Mopane savannas and woodlands are predicted to contribute over 75% of all monoterpenes, primarily from light-dependent emission processes. Rain forests cover only 3.5% of the total area but have high annual emission rates (9.8 g C m−2 yr−1). In the tropical regions with high rainfall, warm temperatures, and high plant productivity throughout the year, the seasonal variation in VOC emissions was small. In subtropical regions, dominated by highly seasonal savannas and grasslands, large variations were predicted, with emissions declining by up to 85% during dry winter periods (June–August) due to low leaf area index after leaf drop.

through the morning hours, with midday fluxes averaging 0.34 mg m � 2 h � 1 and a maximum measured flux of approximately 1.0 mg m � 2 h � 1 . Consistent with these low fluxes, leaf enclosure measurements of woody species within the tower footprint determined that only one isoprene-emitting species, Acacia nigrescens, was present in significant numbers, comprising less than 10% of the woody biomass. Combining enclosure data with species composition and leaf area index data from the site, we estimated that the isoprene emission capacity of the vegetation within the vicinity of the tower was very low, approximately 0.47 mg m � 2 h � 1 , and patchy. Under these circumstances, low and variable fluxes are expected. Additional leaf enclosure measurements, for a total of 121 species, were made at other locations, and approximately 35% of the species was found to emit significant amounts of isoprene. Important isoprene emitting plant families included Caesalpinaceae, Mimosaceae, Papilionaceae, Euphorbiaceae, Moraceae, and Myrtaceae. Twelve members of the important savanna genus Acacia were measured, of which five species, all belonging in Subgenus Aculeiferum, Section Aculeiferum, were found to emit significant amounts of isoprene. In contrast, the plant family, Combretaceae, dominant in many savanna ecosystems, was found to contain no species which emit isoprene. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 1615 Global Change: Biogeochemical processes (4805) Citation: Harley, P., L. Otter, A. Guenther, and J. Greenberg, Micrometeorological and leaf-level measurements of isoprene emissions from a southern African savanna, J. Geophys. Res., 108(D13), 8468, doi:10.1029/2002JD002592, 2003.

Biogenic volatile organic compound (BVOC) emissions were measured in a mopane woodland near Maun, Botswana in January–February 2001 as part of SAFARI 2000. This landscape is comprised of more than 95% of one woody plant species, Colophospermum mopane (Caesalpinaceae). Mopane woodlands extend over a broad area of southern Africa. A leaf cuvette technique was used to determine the emission capacities of the major vegetation and the temperature and light dependence of the emissions. In addition, relaxed eddy accumulation (REA) measurements of BVOC fluxes were made on a flux tower, where net CO2 emissions were also measured simultaneously. Large light-dependent emissions of terpenes (mostly α-pinene and d-limonene) were observed from the mopane woodland. The diurnal BVOC emissions were integrated and compared with the CO2 flux. Monoterpene flux exceeded 3000 μg C m−2 h−1 during the daytime period, comparable to isoprene fluxes and much higher than terpene fluxes measured in most areas. The terpene flux constituted approximately 25% of the diurnal net carbon exchange (CO2) during the experimental period. Other BVOC emissions may also contribute to the carbon exchange.

This paper discusses the relationship between optimum laser power and pulse length to obtain the maximum signal amplitude in pulse position modulation magneto‐optical (MO) recording. The American National Standards Institute standard (X3B11) for 89‐mm disks contains an expression for the maximum allowable optical‐pulse power incident at the surface of the recording disk as a function of laser‐pulse length: Pw=C[(1/tw)+(1/(tw)1/2], where C=75, Pw is the power in mW, and tw is the laser‐pulse duration in nanoseconds. This expression was derived empirically, with C a media characteristic (set to 75 in the standard). To evaluate the adequacy of this empirical equation, disks from five different MO disk suppliers were evaluated for write performance. Having examined different metrics to determine optimum write power for a given laser‐pulse length, the power producing the maximum signal amplitude for 1.56‐μm mark spacings was selected as the performance criterion. Signal amplitude maximizes because of the compe...

Biogenic nonmethane hydrocarbon (NMHC) emissions were investigated at two field sites in the Republic of South Africa that include five important southern African savanna landscapes. Tropical savannas are a globally important biome with a high potential for biogenic emissions but no NMHC emission measurements in these regions or in any part of Africa have been reported. Landscape average hydrocarbon emissions were estimated by characterizing plant species composition and foliar density at each site, identifying and characterizing NMHC emissions of the most abundant plant species, and identifying and characterizing NMHC emissions of plant species with the highest NMHC emission rates. A hand-held portable analyzer proved to be a useful tool for identifying plants with high emission rates. A branch enclosure system, with gas chromatography and flame ionization detector, was used to quantify isoprene and monoterpene emission rates. Emission rates were species-specific and several genera had both high and low emitters. At least some species with high emission rates were identified in most savanna types. High and low emitters were found on both nutrient-rich and nutrient-poor soils. Landscape average emission capacities for the five savanna types range from 0.6 to 9 mg C m-2 h-1 for isoprene and about 0.05 to 3 mg C m-2 h-1 for monoterpenes. The savanna emission rates predicted by existing global models are within the range estimated for these five savanna types.

South African diamonds were found in primary kimberlite source rock in the late 1860’s and early 1870’s when Jagersfontein, Bultfontein, DeBeers, Dutoitspan, and other pipes near Kimberley (Fig. 1) were discovered in rapid succession (Wilson 1982; Janse 1984). Prior to this, stream gravels were the only diamond source worldwide. In 1903, discovery of the Premier kimberlite pipe near Pretoria, 500 km northeast of Kimberley, discredited the then prevalent belief that payable pipes occurred only in the area immediately surrounding Kimberley (Janse 1984). Kimberlite exploration is still proving fruitful in southern Africa, with the Venetia occurrence having been located in the present decade.