ON THE CALIBRATION OF UNDERWATER CAMERAS

Analytical plumbline and serf calibration techniques are applied to the calibration of two underwater cameras: a Rolleifex SLX réseau camera with an Aquamarin WKD-SLX/6006 submarine housing and a Nikonos V underwater camera. The Rolleiflex was fitted with a 50 mm Distagon f/4 lens and the Nikonos with a 28 mm Nikkor-UW f/3.5 lens. Comparisons of the results from the two methods of camera calibration are described. Theoretical differences are predicted for in-air versus in-water values for radial distortion. When these are compared to the actually observed values of distortion, an insight is provided of the precisions claimed for each method of camera calibration.     

Zeolitization of intracaldera sediments and rhyolitic rocks in the 1.25 Ma lake of Valles caldera,New Mexico,USA

Quantitative X-ray diffraction analysis of about 80 rhyolite and associated lacustrine rocks has characterized previously unrecognized zeolitic alteration throughout the Valles caldera resurgent dome. The alteration assemblage consists primarily of smectite–clinoptilolite–mordenite–silica, which replaces groundmass and fills voids, especially in the tuffs and lacustrine rocks. Original rock textures are routinely preserved. Mineralization typically extends to depths of only a few tens of meters and resembles shallow “caldera-type zeolitization” as defined by Utada et al. [Utada, M., Shimizu, M., Ito, T., Inoue, A., 1999. Alteration of caldera-forming rocks related to the Sanzugawa volcanotectonic depression, northeast Honshu, Japan — with special reference to “caldera-type zeolitization.” Resource Geol. Spec. Issue No. 20, 129–140]. Geology and ⁴⁰Ar/³⁹Ar dates limit the period of extensive zeolite growth to roughly the first 30 kyr after the current caldera formed (ca. 1.25 to 1.22 Ma). Zeolitic alteration was promoted by saturation of shallow rocks with alkaline lake water (a mixture of meteoric waters and degassed hydrothermal fluids) and by high thermal gradients caused by cooling of the underlying magma body and earliest post-caldera rhyolite eruptions. Zeolitic alteration of this type is not found in the later volcanic and lacustrine rocks of the caldera moat (≤ 0.8 Ma) suggesting that later lake waters were cooler and less alkaline. The shallow zeolitic alteration does not have characteristics resembling classic, alkaline lake zeolite deposits (no analcime, erionite, or chabazite) nor does it contain zeolites common in high-temperature hydrothermal systems (laumontite or wairakite). Although aerially extensive, the early zeolitic alteration does not form laterally continuous beds and are consequently, not of economic significance.     

Measurements of trace gases emitted by Australian savanna fires during the 1990 dry season

During 18–23 July 1990, 31 smoke samples were collected from an aircraft flying at low altitudes through the plumes of tropical savanna fires in the Northern Territory, Australia. The excess (above background) mixing ratios of 17 different trace gases including CO₂, CO, CH₄, several non-methane hydrocarbons (NMHC), CH₃CHO, NO _x (– NO + NO₂), NH₃, N₂O, HCN and total unspeciated NMHC and sulphur were measured. Emissionratios relative to excess CO₂ and CO, and emissionfactors relative to the fuel carbon, nitrogen or sulphur content are determined for each measured species. The emission ratios and factors determined here for carbon-based gases, NO _x , and N₂O are in good agreement with those reported from other biomass burning studies. The ammonia data represent the first such measurements from savanna fires, and indicate that NH₃ emissions are more than half the strength of NO _x emissions. The emissions of NO _x , NH₃, N₂O and HCN together represent only 27% of the volatilised fuel N, and are primarily NO _x (16%) and NH₃ (9%). Similarly, only 56% of the volatilised fuel S is accounted for by our measurements of total unspeciated sulphur.     

冈底斯朱诺地区中新世板内热隆伸展成矿

位于冈底斯构造成矿带中段西侧的朱诺地区具有良好的成矿前景,已发现有朱诺大型斑岩铜矿床和铁雅铁铜矿点。野外基础地质和矿床地质调查、构造分析和岩石化学的研究表明,朱诺斑岩铜矿床在构造上受近EW向和近SN向伸展断裂控制,时间上属于中新世青藏高原南部板内构造过程,含矿斑岩具有典型的埃达克质岩特征。朱诺及其所在的冈底斯构造成矿带在中新世处于板内构造环境,板内伸展构造—埃达克质岩—斑岩铜矿系统叠加在早期的俯冲—碰撞构造岩石组合之上。与埃达克质岩形成直接相关的下地壳流动导致冈底斯上地壳及下地壳显著加厚,发生部分熔融作用,下地壳物质可能源于地壳减薄的锡瓦利克盆地,流经喜马拉雅,穿过并改造了雅鲁藏布江缝合带中挤入地壳的洋壳地幔岩石,造成被混入洋壳地幔成分的冈底斯下地壳发生部分熔融,形成埃达克质岩浆,上升并顶托冈底斯上地壳,致使冈底斯上地壳先后发生近EW向和近SN向的伸展,在上地壳伸展扩容空间中含矿埃达克质岩浆沿伸展断裂上升、侵位,并富集成矿。     

Fragile empowerment: The dynamic cultural economy of British drum and bass music

This paper discusses the dynamic cultural economy of British drum and bass (D&B) music, which emerged out of Britain’s rave culture in the early 1990s. We suggest that D&B offers insight into more general issues regarding the relation between alternative cultural economies and capitalism. We examine relations between D&B and the mainstream capitalist economy and argue that D&B calls attention to the possibility for alternatives to conventional capitalist relations to survive and possibly thrive without pursuing separation from capitalism. We also theorize D&B as a vehicle towards empowerment regarding the industry segment vis-à-vis the mainstream music industry and also regarding D&B’s practitioners, many of whom can be understood as marginalized discursively and/or materially. However, D&B empowerment is fragile, due in part to technological changes that threaten practices that have helped cultivate innovativeness as well as communal relations. The empowerment of alternative practices is fragile not only for D&B as an industry segment, but also from the vantage point of internal power relations – notably with respect to differences along axes of gender and generation/age. Our conclusions indicate the broader significance of the paper for critical social theory and propose how new research might build on our dynamic view of D&B’s cultural economy.     

Monthly mean winds in the mesosphere at 44S and 78S

A medium frequency partial-reflection spaced-antenna wind radar was installed at Scott Base (78S) on Ross Island, Antarctica, in November 1982. Results from this radar for the period December 1982 to October 1984 inclusive are compared with simultaneous measurements made with a similar radar at Christchurch (44S), N. Z. Monthly mean zonal winds measured at 80 km are compared with recent models for the Southern Hemisphere middle atmosphere. There is a general agreement with the models but there is evidence that the Christchurch winter flow was atypical in 1983.     

Geology of the platanares geothermal area, Departamento de Copán, Honduras

The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids.