Invited article: Digital beam-forming imaging riometer systems

The design and operation of a new generation of digital imaging riometer systems developed by Lancaster University are presented. In the heart of the digital imaging riometer is a field-programmable gate array (FPGA), which is used for the digital signal processing and digital beam forming, completely replacing the analog Butler matrices which have been used in previous designs. The reconfigurable nature of the FPGA has been exploited to produce tools for remote system testing and diagnosis which have proven extremely useful for operation in remote locations such as the Arctic and Antarctic. Different FPGA programs enable different instrument configurations, including a 4 × 4 antenna filled array (producing 4 × 4 beams), an 8 × 8 antenna filled array (producing 7 × 7 beams), and a Mills cross system utilizing 63 antennas producing 556 usable beams. The concept of using a Mills cross antenna array for riometry has been successfully demonstrated for the first time. The digital beam forming has been validated by comparing the received signal power from cosmic radio sources with results predicted from the theoretical beam radiation pattern. The performances of four digital imaging riometer systems are compared against each other and a traditional imaging riometer utilizing analog Butler matrices. The comparison shows that digital imaging riometer systems, with independent receivers for each antenna, can obtain much better measurement precision for filled arrays or much higher spatial resolution for the Mills cross configuration when compared to existing imaging riometer systems.     

Cover slip external cavity diode laser

A 671 nm diode laser with a mode-hop-free tuning range of 40 GHz is described. This long tuning range is achieved by simultaneously ramping the external cavity length with the laser injection current. The laser output pointing remains fixed, independent of its frequency because of the cover slip cavity design. This system is simple, economical, robust, and easy to use for spectroscopy, as we demonstrate with lithium vapor and lithium atom beam experiments.     

Global Tropospheric and Total Ozone Monitoring with a Double-Etalon Fabry-Perot Interferometer. II. Feasibility Analysis

The feasibility of observing global tropospheric and total ozone (O(3)) fields with a double-etalon Fabry-Perot interferometer (FPI) has been assessed. The FPI provides high spectral resolution and high-throughput capabilities that enable observation in pressure-broadened wings of strong O(3) lines while minimizing the impact of undesirable signal contributions (i.e., from the terrestrial surface and interfering species). A retrieval technique has been implemented and is demonstrated for a tropical atmosphere possessing enhanced tropospheric ozone amounts. An error analysis assessing the impact on retrieved O(3) amounts from the most significant uncertainties associated with this particular measurement has been performed, and findings for a tropical atmosphere are presented. Results show the proposed instrumentation to enable a good measurement of absolute ozone amounts and an even better determination of relative changes.     

Etch rate and spectroscopic ablation studies of Er:YAG laser-irradiated dentine

The interaction of a 200-mus Er:YAG laser at 2.94 mum with human molar dentine has been studied by ablation depth rate measurements as well as time-resolved and optical multichannel analyzer emission spectroscopy. Ablation rates indicate a threshold fluence of ~5.2 J cm(-2) for significant material removal with a low-fluence (<20 J cm(-2)) effective optical absorption coefficient of ~700 cm(-1). Deviation from a Beer's law dependence is significant in the range ~20 to ~60 J cm(-2) and indicates a maximum effective plume absorption of ~1200 cm(-1) at ~40 J cm(-2), coinciding with the appearance of strong line and broadband optical emission in the visible region. Time-of-flight emission measurements yield maximum species-resolved ablation velocities of up to ~1.2 x 10(6) cm s(-1), enabling calculation of plasma temperatures. The results suggest that etch-rate characteristics are driven by changes in plume absorption dynamics, which have a strong dependency on incident laser fluence.     

Evidence for the mitochondrial biosynthesis of 3R-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid in the yeast Dipodascopsis uninucleata

The biosynthesis of 3R-hydroxy-5Z,8Z,11Z,14Z-eicosatetraenoic acid (3R-HETE) from arachidonic acid (20∶4n−6) by the hyphal-forming yeast, Dipodascopsis uninucleata, in cell-free enzyme extracts required CoASH, ATP, NAD⁺ and Mg²⁺; 3R-HETE was present as the CoA derivative in enzyme extracts and its biosynthesis was associated with mitochondria. Its synthesis was high from arachidonoyl-CoA (15% conversion of the substrate; 22 nmol mg protein⁻¹·h), but significantly higher from trans-2-arachidonoyl-CoA (53 nmol mg protein⁻¹·min). Aspirin, an inhibitor of prostaglandin endoperoxide synthase synthase (cyclooxygenase), did not significantly inhibit 3R-HETE biosynthesis in enzyme extracts, as opposed to antimycin A (46% inhibition). The chirality of 3-HETE was 95% R and 5% S. 3R-HETE has the same chirality as the products of peroxisomal enoyl-CoA hydratases of Neurospora crassa and Saccharomyces cerevisiae; the difference appears to be that in D. uninucleata the R-enantiomers are synthesized in mitochondria. Exogenously supplied eicosapentaenoic acid was converted to 3-hydroxy 5Z,11Z,14Z,17Z-eicosapentaenoic acid by cell-free enzyme extracts though there was no requirement for a 5Z,8Z-diene structure for the biosynthesis of 3-hydroxylated fatty acids as 3-hydroxy-8Z,11Z,14Z, and 3-hydroxy-11Z,14Z,17Z-eicosatrienoic acids were synthesized from the corresponding fatty acids. We found no evidence for the synthesis of the prostaglandins F_2α and F₂.     

Comparative study of the conditions required to image live human epithelial and fibroblast cells using atomic force microscopy

Successful imaging of living human cells using atomic force microscopy (AFM) is influenced by many variables including cell culture conditions, cell morphology, surface topography, scan parameters, and cantilever choice. In this study, these variables were investigated while imaging two morphologically distinct human cell lines, namely LL24 (fibroblasts) and NCI H727 (epithelial) cells. The cell types used in this study were found to require different parameter settings to produce images showing the greatest detail. In contact mode, optimal loading forces ranged between 2-2.8 x 10(-9) and 0.1-0.7 x 10(-9) (N) for LL24 and NCI H727 cells respectively. In tapping (AC) mode, images of LL24 cells were obtained using cantilevers with a spring constant of at least 0.32 N/m, while NCI H727 cells required a greater spring constant of at least 0.58 N/m. To obtain tapping mode images, cantilevers needed to be tuned to resonate at higher frequencies than their resonance frequencies to obtain images. For NCI H727 cells, contact mode imaging produced the clearest images. For LL24 cells, contact and tapping mode AFM produced images of comparable quality. Overall, this study shows that cells with different morphologies and surface topography require different scanning approaches and optimal conditions must be determined empirically to achieve images of high quality.     

Effect of smelter emission reductions on children's blood lead levels

Trail, British Columbia has been the site of an active lead-zinc smelter for approximately 95 years. Since 1989, the community has been monitoring blood lead levels in children, studying exposure pathways and conducting comprehensive education and case management programs. From 1989 through 1996, mean blood lead levels of pre-school children declined at an average rate of 0.6 microg/dl per year. From 1996 to 1999, mean blood lead levels fell at an average rate of 1.8 microg/dl per year, from 11.5 in 1996 to 5.9 in 1999. The recent rapid decline appears to be mainly attributable to the start-up of a new lead smelter using modern flash-smelting technology in May of 1997. In 1998, the annual arithmetic mean air lead level in Trail was 0.28 microg/m(3), compared with 1.1 microg/m(3) in 1996. Reductions of approximately 50% were observed in lead loadings and concentrations in outdoor dustfall, street dust and indoor dustfall after smelter emissions were reduced. Slight reductions (statistically insignificant) have been observed in carpet dust and soil lead concentrations. During the summer of 2001, the smelting and refining operations at Trail were shut down completely for 3 months. During this period, average air lead levels in Trail dropped to 0.03 microg/m(3). The average blood lead level in Trail pre-school children at the end of the shutdown was 4.7 microg/dl. These results challenge prevailing theories about the relative importance of various environmental lead sources. For example, the US EPA Integrated Biokinetic Uptake Model for Lead (IEUBK), with its emphasis on soil concentrations, would not have predicted the dramatic decline in children's blood lead levels seen in Trail following the reductions in air lead levels. The Trail experience suggests that increased attention should be paid to the importance of active sources of highly bioavailable and mobile lead bearing dusts.     

Characteristics of sludge developed under different loading conditions during UASB reactor start-up and granulation

Sludge characteristics available inside the reactor are of vital importance to maximize advantages of UASB reactor. The organic loading rate and sludge loading rate applied during start-up are among the important parameters to govern the sludge characteristics. Effects of these loading rates on the characteristics of the sludge developed are evaluated in six laboratory scale UASB reactors. The sludge characteristics considered are VSS/SS ratio of the sludge, sludge volume index, specific gravity, settling velocity and metal contents of the sludge developed under different loading rates. The experimental results indicate that, for developing good characteristics sludge, during primary start-up from flocculent inoculum sludge, organic loading rate and sludge loading rate should be in the range of 2.0-4.5 kg COD/m3 d and 0.1-0.25 kg COD/kg VSS d, respectively (chemical oxygen demand, COD). Proper sludge granulation and higher COD removal efficiency will be achieved by these loading rates.     

Degradation of phenol using Co- and Co,F-doped PbO(2) anodes in electrochemical filter-press cells

A comparative study on the electrooxidation of phenol in H(2)SO(4) medium using pure PbO(2) or F-, Co- and Co,F-doped PbO(2) electrodes in filter-press cells was carried out. The oxide films were obtained by galvanostatic electrodeposition using an electrolytic bath containing sodium lauryl sulfate as additive and Pb(2+), F(-), Co(2+) or Co(2+)+F(-), under magnetic stirring (to obtain 4-cm(2) electrodes) or ultrasound waves (to obtain 63-cm(2) electrodes). The best results were attained with PbO(2) electrodes doped with a low-Co content (1mM Co(2+) in the electrolytic bath) along with F(-): the chemical oxygen demand (COD) and the total organic carbon content (TOC) of the simulated wastewaters were removed by about 75% and 50%, respectively. When pure PbO(2) electrodes were used, the COD and TOC removals were about 60% and 45%, respectively. For the smaller electrodes, an average current efficiency (ACE) and an energy consumption (EC) of about 16% and 70 kWh kg(COD)(-1), respectively, were obtained. For the larger electrodes, the ACE and EC values were about 18% and 105 kWh kg(COD)(-1), respectively. Stability tests of the electrodes showed that they are suitable for use in the electrochemical treatment of phenol wastewaters.