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.     

Spectrophotometry of comet West (1975n) after the perihelion passage

In the wavelength range 350 to 650 nm, the flux distribution of comet West (1975n) is presented for various dates following perihelion passage. The variations with heliocentric distance, in the flux of the emission features of the CN band at 388 nm, the C₂ bands at 474 nm, 516 nm and 563 nm and Na at 589 nm, have been discussed. It is concluded that the comet was dust rich.     

Theory and operation of the split langmuir probe

An instrument, the split Langmuir probe, has been developed to make in situ measurements of current density and plasma bulk flow. The split Langmuir probe consists of two conducting elements that are separated by a thin insulator that shield each other over a 2π solid angle, and that are simultaneously swept from negative to positive potentials with respect to the plasma. By measuring the current to each plate and the difference current between plates, information can be obtained on the plasma's current density, bulk flow, electron temperature, and density. The instrument was successfully test flown from Fort Churchill on 2 August 1968, with results in reasonable agreement with those from another experiment on the same rocket. Sources of error indicated by these results include plate area differences, plate work function differences, input resistor differences, and probe wake effects. The error signal in the difference current data due to plate work function differences rose to a sharp maximum at plasma potential, which served the useful purpose of precisely marking plasma potential. Possible changes in probe geometry, sweep rate, and telemetry designed to reduce these errors are discussed.     

A world without Greenland: impacts on the Northern Hemisphere winter circulation in low- and high-resolution models

To investigate the effect of Greenlands orography on the northern hemisphere winter circulation experiments with an atmospheric GCM are conducted: a perturbed integration where standard orography is reduced to sea level in the Greenland area is compared to a standard orography control integration. The outcome of these experiments suggests that the existence of high mountains at Greenland causes a reinforcement of the stationary wave field in the Atlantic sector, colder temperatures to the west of Greenland and warmer temperatures to the east and south, over the North Atlantic. The impact on the flow field cannot be understood in the framework of standing Rossby waves, but it indicates a resonance between remotely forced stationary waves and local (thermo-) dynamics. The pattern of the North Atlantic Oscillation (NAO), in particular the northern centre, lies further to the east in the flat-Greenland experiment compared to the control run and the observations. Together with the fact that the climatological low-pressure system around Iceland hardly shifts, this suggests that the location of the NAO is not necessarily tied to the time mean pressure distributions. Considering the model resolution as a parameter, experiments with a high resolution (T106) suggest that the near-field changes are represented sufficiently by a T42 resolution, a standard resolution used in state-of-the-art coupled climate models. In contrast, far-field changes depend critically on model resolution. Hemispheric circulation and temperature changes differ substantially from low to high resolution, and generalized statements about the impact of Greenlands orography cannot be made.     

Photometric and spectrophotometric observations of the classical symbiotic star YY Her during its return to quiescence

We present new photometric UBVRI and spectroscopic observations of the symbiotic star YY Her during its return to quiescence after a strong outburst in 1993. High-resolution spectra of YY Her at similar phases at outburst maximum ?=0.48) and in quiescence ?=0.37) are presented for the first time. The ephemeris of YY Her has been refined P=586^d). The last two observed minima (in 1999 and 2000) differed radically in shape from the 1997 minimum described previously. Both were sharp and deep $(\Delta U \sim 1\mathop .\limits^m 6, \Delta V \sim 0\mathop .\limits^m 9)$ . To explain this shape of the V light curve, which is only slightly affected by nebular emission, it should be assumed that the cool component of YY Her fills much of its Roche lobe and has a hot spot on the hemisphere facing the hot component. The emission spectrum rich in Fe II lines, which is characteristic of symbiotic stars, was observed during the outburst, but high-ionization lines (He II λ4686) were also observed. The He I λλ5876, 7065 lines exhibit distinct P Cyg profiles; the centers of the absorption components are shifted from the emission ones by V _r≈100 km s^?1, suggesting moderate outflow velocities.     

High Acetone Concentrations throughout the 0–12 km Altitude Range over the Tropical Rainforest in Surinam

Airborne measurements of acetone were performed overthe tropical rainforest in Surinam(2°–7° N, 54°–58° W, 0–12 kmaltitude) during the LBA-CLAIRE campaign in March1998, using a novel proton transfer reaction massspectrometer (PTR-MS) that enables the on-linemonitoring of volatile organic compounds (VOC) with ahigher proton affinity than water. The measuredacetone volume mixing ratios ranged from 0.1 nmol/molup to 8 nmol/mol with an overall average of 2.6nmol/mol and a standard deviation of 1.0 nmol/mol. Theobserved altitude profile and correlations with CO,acetonitrile, propane and wind direction are discussedwith respect to potential acetone sources. No linearcorrelation between acetone and CO mixing ratios wasobserved, at variance with results of previousmeasurement campaigns. The mean acetone/CO ratio(0.022) was substantially higher than typical valuesfound before. The abundance of acetone appears to beinfluenced, but not dominated, by biomass burning,thus suggesting large emissions of acetone and/oracetone precursors, such as possibly 2-propanol, fromliving plants or decaying litter in the rainforest.     

The 1997/1998 mass mortality of corals: effects on fish communities on a Tanzanian coral reef

The abnormally high surface temperatures in the world's oceans during 1997/1998 resulted in widespread coral bleaching and subsequent coral mortality. An experiment was performed to study the effects of this coral mortality as well as the influence of the structural complexity on fish communities on a Tanzanian coral reef. Changes in fish communities were investigated on plots of transplanted corals after 88% of these corals had died. A distinct shift in fish community composition was found, although diversity was not affected. Fish abundance rose by 39% mostly due to an increase in herbivores, which seemed to benefit from enhanced algal growth on the dead corals. Fish abundance, species diversity and community composition were also strongly influenced by the structural complexity provided by the live and dead corals. This suggests that a coral reef can support abundant and diverse fish populations also after the corals have died as long as the reef structure is sustained.     

Thoughts on the Measurement and Calculation of Geogenetic Depth

The method of determining the depth of geological events is based on the geobarometer method. According to this method, a depth to a certain position is obtained in such a way that the pressure at that position is divided by the specific weight(density) of the overlying rock formations, called the "W/SW" method in this paper. This method follows the principle of hydrostatics, assuming that rocks in this case are in a static fluid state(standard state) rather than a solid state. If so, only pressure could be measured from the rocks because the latter does not exist in a hydrostatic