RXTE spectroscopy of GRS 1915+105

The galactic superluminal motion source GRS 1915+105 has been extensively observed with the RXTE satellite over the last two years. More than 250 RXTE pointings have been performed until mid-May 1998 with more than 1.5 Msec exposure time on roughly a weekly basis. Here we report on first results of our spectral analysis of a major part of these pointed RXTE observations. We establish the existence of at least 5 spectral components and present the changes of these components over the last two years.     

Water uptake by two river red gum (Eucalyptus camaldulensis) clones in a discharge site plantation in the Western Australian wheatbelt

The heat-pulse technique was used to estimate year-long water uptake in a discharge zone plantation of 9-year-old clonal Eucalyptus camaldulensis Dehnh. near Wubin, Western Australia. Water uptake matched rainfall closely during weter months but exceeded rainfall as the dry season progressed. Average annual water uptake (1148 mm) exceeded rainfall (432 mm) by about 2.7 fold and approached 56% of pan evaporation for the area. The data suggest that at least 37% (i.e. (1/2.7) × 100) of the lower catchment discharge zone should be planted to prevent the rise of groundwater.

Water uptake varied with soil environment, season and genotype. Upslope trees used more water than did downslope trees. Water uptake was higher in E. camaldulensis clone M80 than in clone M66 until late spring. The difference reversed as summer progressed. Both clones, however, have the potential to dry out the landscape when potential evapotranspiration exceeds rainfall. This variation in water uptake within the species indicates the potential for manipulating plantation uptake by matching tree characteristics to site characteristics.

Controlled experiments on the heat-pulse technique indicated accuracy errors of approximately 10%. This, combined with the ability to obtain long-term, continuous data and the superior logistics of use of the heat-pulse technique, suggests that results obtained by it would be much more reliable than those achieved by the ventilated chamber technique.     

An oxygen isotope — Climate record from the Law Dome,Antarctica

Ice cores from a 473 m deep borehole at the summit of the Law Dome, Antarctica have been analysed for oxygen isotope ratio variations. Values averaged over each core section (nominally 2 m long) are used to compile a continuous record for climatic studies and the fine detail measurements which show annual variations are used to establish a date of deposition versus depth relationship. The temperature record derived from the isotope data shows a warm period from 300 to 1000 AD followed by a cooling which, after a partial recovery between 1400 and 1600 AD reaches a maximum around 1800. Temperatures then increase during the nineteenth and twentieth centuries to almost the same values as prior to 1000 AD.     

Heat flow in Eastern Egypt: The thermal signature of a continental breakup

The Red Sea is a modern example of continental fragmentation and incipient ocean formation. Heat flow data have been collected from eastern Egypt to provide information relating to the mode and mechanism of Red Sea opening. Preliminary heat flow data, including new data reported here, are now available from twenty-five sites in eastern Egypt and one site in western Sinai. A pattern of low to normal heat flow (35–55 mW m⁻²) inland with high heat flow (75–100 mW m⁻²) in a zone within 30 to 40 km of the coast is indicated.Moderately high heat flow (around 70 mW m⁻²) is indicated for the Gulf of Suez. The coastal zone thermal anomaly appears continuous with high heat flow previously reported for the Red Sea shelf. Heat production data indicate that the coastal thermal anomaly is not primarily related to crustal radiogenic heat production. The effects of rapid erosion may contribute to the anomaly, but are not thought to be the primary cause of the anomaly. If the anomaly is caused by lateral conduction from hot, extended, offshore lithosphere, the extension must have been active for the last 30 Ma or so, and a minimum of 100% extension is indicated. Alternatively, the anomaly is primarily caused by high mantle heat flow causing lithospheric thinning, centred beneath the Red Sea. The Red Sea is probably underlain by dominantly basic crust, formed either by intrusion into attenuated continental crust or sea-floor spreading, and for most purposes the crust formed in these two modes of extension may be essentially indistinguishable. Fission-track ages from eastern Egypt indicate that uplift started prior to, or at latest at the time of initial Red Sea opening, and this result, together with thermo-mechanical considerations, suggests an active asthenospheric upwelling beneath the Red Sea and high temperature in the lithosphere prior to extension.     

Acute toxicity of mine tailings to four marine species

Acute toxicity bioassays were conducted on mine tailings produced by pilot plant testing for the proposed Quartz Hill molybdenum mine, which will be situated near Ketchikan, Alaska. Tailings bioassays were conducted in seawater with juvenile coho salmon (Oncorhynchus kisutch), mussel larvae (Mytilus edulis), infaunal amphipods (Rhepoxynius abronius), and euphausiids (Euphausia pacifica). The same general range of mine tailings concentrations was acutely toxic to all four test species with acute effects observed between 61 000 to 277 000 mg l^?1 (wet wt) tailings solids (range of 95% confidence limits for LC₅₀ and EC₅₀ values). Chemical analyses of bioassay test solutions and leaching test solutions were conducted for metals (including Cd, Cu, Pb, Zn, Mn and Mo), EPA Priority Pollutant base/neutral organics, and more general parameters such as sulphate, nitrate/nitrite, cyanides, phosphate and ammonia. Parameters possibly contributing to the observed toxicity were complex contaminant mixtures including total suspended solids and heavy metals. The present study provides information related to the marine disposal of mine tailings and shows that these mine tailings present a relatively low level of acutely toxic effects.     

Collisional plateaus

In the fifteen years since the importance of collisional plateaus with thickened continental crust began to be recognized as one of the inevitable consequences of the processes of plate tectonics, rapid progress in their understanding has come from studies of the world's only active terminal collision zones in the Himalayan-Tibetan and Turkish-Iranian plateaus.Ancient collisional plateaus are being recognized throughout the geological record (back to 3.8 Ga) from the occurrence of extensive areas (typically > 500,000 km²) of 8 kbar metamorphism in granulite facies or from the occurrence of extensive areas of higher level minimum-melt composition granite rocks whose isotopic signatures indicate reactivation of existing continental crust rather than addition of new crust from the mantle at the time of collision. Recognition of strike-slip faulting in the ancient collisional plateau areas indicates that “tectonic escape” may have been as important in the past as it is today.Earth may not be the only planet on which collisional plateaus are important. The highlands of Venus (approximately 7% of the surface with elevations over 1.5 km above mean planetary radius) can only exist as a result of crustal thickening, and not as a product of lithospheric thinning. Most of these highlands can be explained by models involving volcanic construction. However, the highest peaks, including Maxwell Montes, the highest mapped area of Venus rising over 10 km above mean planetary radius, require much greater crustal thickening to support them than can reasonably be explained by a volcanic mechanism. Geological features of Maxwell Montes inferred from radar images suggest some analogy between Maxwell Montes and the Tibetan plateau.It is somewhat paradoxical that extensional tectonics are commonly associated with continental collision, and that collision-related rifts may be the only sites where the uppermost layers of a collision-thickened crust are preserved from erosion. Extensional stress fields are generated during continental collision, primarily in areas associated with strike-slip faulting and “tectonic escape”. Additional extensional stresses are gravitationally generated associated with the topography and thickened crust in a collision zone. Tectonically thickened crust is particularly susceptible to rifting as its lithosphere is weak as a result of heating associated with magmatism. This lithosphere is also compositionally weak because of the relatively thick crust, dominated by a weak quartz rheology, and thin mantle lithosphere, dominated by a strong olivine rheology, in comparison with a lithosphere with a more normal crustal thickness. Thus, the common association of rifts and collision zones may be a consequence of both stresses generated during collision and modification of the lithosphere by collision.     

Cut Flowers in Warsaw

Cut flowers production around Warsaw depends mainly on very intensive methods, particularly the use of glasshouses, and includes a number of highly specialized farms. It is the result of a remarkably high level of demand in Poland and of the development of an export industry. It plays an important role in an agricultural system in which the production possibilities for very small farms are limited. Most production is in private hands and depends on the application of relatively large quantities of capital with a considerable element of risk. Farmers grow flowers at varying levels of intensity and with varying degrees of specialisation. A particular spatial structure within the general geographical distribution of intensive agriculture around Warsaw appears to have resulted. An attempt is made to indicate some of the elements in this structure by the use of published data for flowers production and for the taxation of private holdings by small administrative districts — the gminy or local communes. Examination of inputs indicates major constraints. The industry reached a peak in 1981. If it were to expand again attention should be paid to existing spatial diseconomies and the possibilities of relocation.     

Testing the resolution of a 3D velocity tomogram across the Chicxulub crater

An integrated offshore/onshore reflection and refraction experiment was shot across the Chicxulub impact crater in 1996. The refraction data were previously inverted in 3D using first-arrival travel-time tomography. A regularized inversion, in which both data misfit and model roughness are minimized simultaneously, was used to determine a smooth velocity tomogram across the inner crater region. However, the experimental geometry for the refraction data was irregular, causing concern that this velocity model might not be well resolved. In this paper, we present a suite of checkerboard tests to investigate the lateral resolution of our velocity model. The Chicxulub crater is located partly onshore and partly offshore, with its centre close to the Yucatan coastline in Mexico. The shallow water limited acquisition of marine reflection data to distances of not closer than 25 km from the crater centre, and the centre of the structure is imaged with refraction data only. Intriguing velocity anomalies were observed across the central crater region, providing constraints on the lithological and structural form of Chicxulub. A high-velocity body within the central crater is most likely to represent lower-crustal rocks that were stratigraphically uplifted during the formation of this complex crater. The concave shape of this stratigraphic uplift suggests clues to the mechanics of large-crater collapse—the rocks appear to have moved upward and outward. An inward-dipping zone of lowered velocity has been interpreted as delimiting the outer edge of a central zone of melt-rich rocks. The resolution tests presented here indicate that these observed velocity anomalies are likely to be real.     

Bundle Adjustment with Self–Calibration Using Straight Lines

Increased use of digital imagery has facilitated the opportunity to use features, in addition to points, in photogrammetric applications. Straight lines are often present in object space, and prior research has focused on incorporating straight–line constraints into bundle adjustment for frame imagery. In the research reported in this paper, object–space straight lines are used in a bundle adjustment with self–calibration. The perspective projection of straight lines in the object space produces straight lines in the image space in the absence of distortions. Any deviations from straightness in the image space are attributed to various distortion sources, such as radial and decentric lens distortions. Before incorporating straight lines into a bundle adjustment with self–calibration, the representation and perspective transformation of straight lines between image space and object space should be addressed. In this investigation, images of straight lines are represented as a sequence of points along the image line. Also, two points along the object–space straight line are used to represent that line. The perspective relationship between image– and object–space lines is incorporated in a mathematical constraint. The underlying principle in this constraint is that the vector from the perspective centre to an image point on a straight–line feature lies on the plane defined by the perspective centre and the two object points defining the straight line. This constraint has been embedded in a software application for bundle adjustment with self–calibration that can incorporate point as well as straight–line features. Experiments with simulated and real data have proved the feasibility and the efficiency of the algorithm proposed.