High-precision continuous-flow measurement of delta13C and deltaD of atmospheric CH4

We describe our development of a CH4 preconcentration system for use with continuous-flow gas chromatograph combustion isotope ratio mass spectrometry (GC/C/IRMS). Precision of measurement of delta13C-CH4 is 0.05/1000 (1sigma) on multiple 60-mL aliquots of the same ambient air sample. The same front-end on-line CH4 preconcentration system allows us to measure deltaD of CH4 by gas chromatography IRMS when the combustion furnace is replaced with a pyrolysis oven (GC/P/IRMS). Precision of measurement for deltaD-CH4 is 1.5/1000 (1sigma) using 120 mL of ambient air based on multiple aliquots of the same air sample. These are the first reported measurements of atmospheric CH4 using GC/P/IRMS methodology. Each isotope analysis can be made much more rapidly (30-40 min) than they could using off-line combustion of an air sample (1-6 h) followed by conventional dual-inlet IRMS measurements (12-20 min), while requiring much less total volume and retaining a comparable level of precision and accuracy. To illustrate the capabilities of our preconcentration GC/C/IRMS system, we compare the results of measurement of 24 background air samples made using both GC/C/IRMS and conventional vacuum line/dual-inlet IRMS methodology. The air samples were collected on a shipboard air sampling transect made across the Pacific Ocean in July 2000 and are part of an ongoing atmospheric CH4 research program. The average difference between the two methods of IRMS analyses on these 24 samples is 0.01 +/- 0.03/1000 (95% confidence interval) for delta3C-CH4. These are the first measurements to be reported of air samples directly intercompared for delta13C-CH4 using both GC/C/IRMS and dual-inlet IRMS measurement methodology. Measurement of deltaD-CH4 of these air samples is also presented as an illustration of the ability of this system to resolve small isotopic differences in remote air. High-precision measurement of delta13C and deltaD of atmospheric CH4 made using our coupled preconcentration GC/IRMS system will greatly improve our ability to utilize isotopic data in understanding spatial and temporal changes in atmospheric CH4 and the biogeochemistry of its sources and sinks.     

Thorium in the workplace: results from a European-based measurement comparison project

A Series of comparisons were conducted to test the capabilities of a range of metrological techniques and analytical laboratories engaged in the assay of thorium in the workplace. The results of these exercises are presented together with the decision criteria used to determine whether results are significantly different from the true value. The discussion highlights those aspects which warrant closer and further attention.     

Nonylphenol affects gonadotropin levels in the pituitary gland and plasma of female rainbow trout

Female rainbow trout (Oncorhynchus mykiss) were exposed to 4-nonylphenol (NP) at (mean measured) concentrations of 0.7, 8.3, and 85.6 micrograms/L for 18 weeks, during early ovarian development. Fish were sampled sublethally every six weeks, and terminal samples were taken at 18 weeks. NP induced an estrogenic effect (the synthesis of vitellogenin) at concentrations of 8.3 and 85.6 micrograms/L. An effect on gonadotropin synthesis and secretion was also observed. Plasma follicle stimulating hormone (FSH) levels and FSH gene expression in the pituitary were the most sensitive endpoints assessed, being reduced at the lowest dose employed (0.7 microgram NP/L). Pituitary gland luteinizing hormone (LH) content was significantly lower in fish exposed to 85.6 micrograms NP/L, and LH gene expression was suppressed in fish exposed to 8.3 and 85.6 micrograms NP/L. In contrast, plasma LH concentration increased in these fish, but by a very minor absolute amount, and returned to control levels by the final sampling time. Gonadal development ceased in the fish exposed to 85.6 micrograms NP/L, and steroidogenesis in these fish was also markedly inhibited. Although the mechanisms underlying these responses are unknown, this study demonstrates that NP has adverse effects on pituitary function that can result in inhibition of ovarian development.     

High performance GaAs MESFETs with molecular implanted and optimized lowly-doped drain structure for maximized speed, gain and breakdown performance

GaAs MESFETs with novel lowly-doped drain structures have been developed utilizing molecular implants of silicon trifluoride. Short-channel effects in the 1/4 μm enhancement- and depletion-mode transistors have been suppressed with drain-induced barrier height lowering of less than 70 mV/V and pinch-off voltage shifts of less than 220 mV as the gate length was scaled from 1.0 to 1/4 μm. The 3-terminal breakdown, the transconductance to output conductance ratio, and the unity current gain, cut-off frequency were simultaneously optimized. The E-mode device possessed breakdown of >10 V, G_m · R_ds > 9.5, F_t > 55 GHz, and nominal on-resistance of 2.1 Ω mm while the D-mode device had breakdown >10 V, G_m · R_ds > 6.0, F_t > 45 GHz, and nominal on-resistance of 1.9 Ω mm. These optimized transistors enabled the realization of a variety of low-power digital and high-power mixed signal circuits, using 3-level source-coupled transistor and common-mode logic, such as laser and electro-optic drivers, highly integrated transceivers, multiplexers, demultiplexers, and clock data recover circuits.     

The afferent neural response to electrotactile stimuli: preliminary results.

We recorded action potentials from three RA fibers innervating primate fingerpad, while applying electrotactile (electrocutaneous) stimulation. Negative pulses required 1.3-1.5 times more current than positive ones for entrainment. The strength-duration time constant was approximately 151 micros. Suprathreshold sinusoidal vibration synchronized to 30-Hz electrotactile pulses changed the electrotactile entrainment current slightly, indicating a possible electrical-mechanical transduction interaction.     

THERMODYNAMICS OF MOISTURE SORPTION IN ALFALFA PELLETS

ABSTRACT

Experimental data on sorption isotherms of alfalfa pellets were used to determine the thermodynamic functions (differential heat of sorption, spreading pressure, net integral enthalpy and entropy) of the pellets. The thermodynamic functions were then utilized in modeling the specific heats of pellets as a function of moisture content. The estimated values of the thermodynamic functions at different moisture contents confirmed the results of an earlier study on the influence of moisture sorption on the physical integrity of the pellets. The changes in the thermodynamic properties and physical integrity were prominent when the moisture of the pellets were between 0.10 and 0.12 (mass fraction basis). Using the differential heat of sorption, it was determined that alfalfa pellets have higher affinity for moisture uptake when compared to wheat and lentils. The specific heat of the solids of alfalfa pellets had a parabolic relationship with moisture whereas the specific heat of water fraction increased linearly with moisture content of the pellets.     

The use of remotely sensed data to detect channel hydromorphology; River Tummel,Scotland

Colour aerial photography and multi‐spectral imagery acquired from airborne platforms for the River Tummel, Scotland, was used in conjunction with field survey to assess the feasibility of monitoring hydromorphology and human alteration within the river corridor. The study was undertaken to investigate the possibility of remotely sensing the physical status of a nation's rivers at the national scale to comply with the requirement of the European Water Framework Directive. Visual assessment and unsupervised and supervised automated classifications of the imagery were undertaken and compared with field survey data. In the absence of overhanging vegetation canopies most features above the water line of interest were visible on the imagery. Below the water line, morphology and substrate composition together with bank materials on vertically cut banks are less easily detected. The overall accuracy of automated classification procedures, compared to field survey, was 60% for the colour aerial photography and 68% for the multi‐spectral imagery. Supervised classification was superior to unsupervised classification procedures. Sun glint on water surfaces and shadows caused by high banks, trees and buildings were observed as the cause of most misclassification of features. Overall, the study demonstrates that remotely sensed digital imagery has the potential to allow panoptic mapping of river hydromorphology and human impacts. The possibilities and constraints, in light of the findings of this study, are discussed. In the context of new legislation which requires environmental protection agencies to have robust tools for monitoring the physical status, as part of meeting the objective of good ecological status, of rivers across an entire nation, remote sensing appears to provide a way forward. Copyright © 2004 John Wiley & Sons, Ltd.     

Reaction engineering studies of methane coupling in fluidised-bed reactors

The oxidative coupling of methane has been conducted in 30 and 60mm dia. fluidised-bed reactors. Methane conversions as high as 40% were achieved at isothermal conditions using methane/oxygen mixtures without diluents. At the same contact time the two reactors had similar selectivities to hydrocarbons. At 850°C the hydrocarbon selectivity decreased dramatically with increasing contact time but this effect was much less severe at lower temperatures. Axial gas concentration profiles through the catalyst bed in the 60mm reactor indicated that at 850°C there was a rapid consumption of oxygen and formation of products in the bottom section of the bed followed by a net loss of hydrocarbon in the oxygen-free zone. This loss was due to carbon formation on the catalyst which was circulated back to the oxygen-containing zone of the bed where the carbon was combusted.