ESTIMATION OF ERRORS IN ABSORBANCE RATIO MEASUREMENTS

Ratio measurements are commonly used to address a variety of analytical problems in environmental,forensic and pharmaceutical laboratories.In absorbance ratioing techniques,analytical chemists rely onthe spectral features of the analyte(s)of interest.The absorbances at two wavelengths are monitored andthe ratio of these two absorbances is computed.This ratio is then used to confirm the identity of theanalyte(s)of interest,the purity of a product or the overlap of chromatographic peaks.These decisionsoften have far-reaching consequences(e.g.the identification of the source,biogenic or petrogenic,ofhydrocarbons in biological tissues or water).Given the cost and the liabilities associated with suchdecisions,it is unfortunate that these ratios are seldom reported with any statistical confidence.Thepurpose of this study is to delineate the parameters that affect absorbance ratio measurements.Themodels that can be used to estimate the statistical confidence in these measurements are derived andevaluated experimentally.The results show that these models can estimate the relative standard deviationsin absorbance ratios accurately.They can also estimate the effect of signal-to-noise ratio and the choiceof wavelengths on the precision of absorbance ratios.     

Kenn Plateau off northeast Australia: a continental fragment in the southwest Pacific jigsaw

The submarine Kenn Plateau, with an area of about 140 000 km², lies some 400 km east of central Queensland beyond the Marion Plateau. It is one of several thinned continental fragments east of Australia that were once part of Australia, and it originally fitted south of the Marion Plateau and as far south as Brisbane. It is cut into smaller blocks by east- and northeast-trending faults, with thinly sedimented basement highs separated by basins containing several kilometres of sediment. In the Cretaceous precursor of the Kenn Plateau, Late Triassic to Late Cretaceous basins probably rested unconformably on Palaeozoic to Triassic rocks of the New England Fold Belt. Rift volcanism was common on the northern plateau and was probably of Early Cretaceous age. Late Cretaceous extension and breakup were followed by Paleocene drifting, and the Kenn Plateau moved to the northeast, rotated 30° anticlockwise and left space that was filled by Tasman Basin oceanic basalts. During these events, siliciclastic sediments poured into the basins from the continental mainland and from locally eroding highs. After a regional Late Paleocene to Early Eocene unconformity, siliciclastic sedimentation resumed in proximal areas. In deep water, radiolarian chalks were widely deposited until biosiliceous sediment accumulation ended at the regional Late Eocene to Early Oligocene unconformity, and warming surface waters led to accumulation of pure biogenic carbonates. Calcarenite formed in shallow water on the margins of the subsiding plateau from the Middle Eocene onward. Some seismic profiles show Middle to Late Eocene compression related to New Caledonian obduction to the east. Hotspots formed parts of two volcanic chains on or near the plateau as it moved northward: Late Eocene and younger volcanics of the Tasmantid chain in the west, and Late Oligocene and younger volcanics of the Lord Howe chain in the east. As the volcanoes subsided, they were fringed by reefs, some of which have persisted until the present day. Other reefs have not kept up with subsidence, so guyots formed. The plateau has subsided 2000 m or more since breakup and is now subject solely to pelagic carbonate sedimentation.     

北祁连东部两类Ⅰ型花岗岩定年及其地质意义

北祁连东部早古生代地层中产出两种特征不同的I型花岗岩类,其一以井子川岩体为代表,暗色矿物以角闪石为主,稀土总量为90×10~(-6)～106×10~(-6),轻重稀土比值小于8,锆石的SHRIMP年龄为464±15Ma,岩体形成的构造环境类似于岛弧;其二是以黄羊河岩体为代表,暗色矿物以黑云母为主,稀土总量为214×10~(-6)～250×10~(-6),轻重稀土比值大于8,锆石的LA-ICP-MS年龄为383±6 Ma,岩体形成于碰撞后环境。     

Effects of camel grazing on the ecology of small perennial plants in the Dubai (UAE) inland desert

Camel grazing is recognized as a primary cause of ecological degradation in the UAE. A study of perennial plant species <1 m in height was conducted along a fence separating continuously camel grazed land from land in which camels had been replaced by oryx and gazelle species for 5 years (Al Maha). Vegetation regeneration in Al Maha in the absence of camels was considerable on all substrates (gravel, stable sand, and semi-stable sand) but was greatest on the gravel substratum, indicating that ecology in this habitat is most at risk. Observed regeneration was primarily through vegetative reproduction and growth of existing plants, showing that existing species can tolerate heavy grazing. Therefore, an equilibrium grazing model of continuous and reversible vegetation dynamics is most suitable for management of this ecological zone. Species richness was greater in Al Maha due to the greater number of plants, but biodiversity was unaffected. There was some evidence of localized dune stabilization within Al Maha due to increased vegetative cover. Further recovery of vegetation within Al Maha is discussed. This study highlights the need for reduced grazing pressure throughout the Dubai inland desert, and in particular on gravel substrata.     

A comparison of the temperature coefficients of electrical conductivity of Atlantic and Pacific seawaters

The Practical Salinity Scale 1978 (PSS) defines the relationship among salinity, electrical conductivity, temperature, and pressure. Strictly speaking, the PSS is only applicable to waters with the same relative chemical composition as standard seawater. We have tested the predictions of the PSS for samples of Atlantic and Pacific waters. The results indicate that the PSS is valid for these natural seawaters over the defined temperature range of the scale.     

Designing an archival Satellite transmitter for life-long deployments on oceanic vertebrates: the life history transmitter

Despite the widespread use of sophisticated telemetry transmitters in behavioral, physiological and ecological studies, few studies on population dynamics of oceanic vertebrates use such technology, primarily due to the difficulty of obtaining multi-year records from individual animals. We present the first telemetry transmitter specifically designed for collecting vital data from marine vertebrates over extended periods, up to a decade. The implantable Life History Transmitter records data throughout the life of a host animal. After the host animal dies, the tag is extruded, and, while floating on the ocean or lying on a beach, transmits previously stored data to orbiting satellites. For tags relying solely on end-of-deployment transmission, reliability and proper recognition of tag state is crucial. The Life History Transmitter uses heuristic tag state determination, in combination with simple error detection and fault tolerance measures, to increase tag reliability and likelihood of data recovery. We used a computer simulation of tag deployments and various sensor failures on a PC platform, in combination with time-accelerated simulations running on the actual deployment platform, to test the functionality of fault tolerance and error detection protocols.     

The extension of the Practical Salinity Scale 1978 to low salinities

The Practical Salinity Scale (PSS) 1978 is defined only for salinities within the range 2-42. We have investigated the relationship between mass-determined salinity, electrical conductivity, and temperature for salinities between 0 and 2 with the aim of developing an extension to the Practical Salinity Scale 1978. The paper presents our data, on the basis of which the following correction is proposed to extend the validity of the equations defining the scale to the entire 0-42 range:S=summin{i=0}max{5} (a_{i}+b_{i}f(t))R_{t}^{i/2}-frac{a_{0}}{1 + 1.5x + x^{2}}-frac{b_{0}f(t)}{1+y^{1/2} + y + y^{3/2}}wheref(t)=frac{(t-15)}{1 + k(t-15)x=400R_{t}y=100R_{t}and the constanta_{i}, b_{i}, andkare defind by the Practical Salinity Scale 1978.