Mesh Aperture Research Articles

Planktonic communities as indicators of water quality in mangrove lagoons; a Jamaican case study

1 - In mangrove lagoons, where natural conditions of high turbidity, detritus and microbiological activity combined with low light render traditional water quality indices unreliable, the planktonic community is proposed as a more appropriate and accurate index of eutrophication status. 2 - Over a 12 month period, monthly sampling was conducted at 9 stations representing different degrees of eutrophication. 3 - Phytoplankton size fractionated biomass, species composition and abundance as well as zooplankton total abundance, species composition and abundances of selected groups were examined along with depth, temperature, salinity, dissolved oxygen, pH, particulate organic matter, and reduction / oxidation potential (redox). 4 - Phytoplankton were collected using a horizontal niskin whole water sampler, zooplankton hauls (vertical/oblique) were taken using a modified Wildco net (158 &µ956;m mesh aperture 0.2 m hoop diameter) and a Hydrolab Surveyor IV Water Quality Data System was used to collect physic-chemical data in situ. 5 - While dissolved oxygen, salinity and pH demonstrated potential for use as water quality indicators, particulate organic matter, redox and temperature demonstrated inconclusive variations or insignificant differences between lagoons of known water quality. 6 - Phytoplankton biomass (Chlorophyll a) was among the most reliable planktonic indices distinguishing four groups of stations with different water qualities: oligotrophic (0.21-0.55 mg m -3 ) mesotrophic (0.57 – 2.55 mg m -3 ) eutrophic (3.00 to 6.55 mg m -3 ) and extremely eutrophic (>31.17 mg m -3 ). 7 - This was attributed to diatom and dinoflagellate cells of differing sizes being able to characterise eutrophication even after the source of eutrophication had dissipated and while physico-chemical parameters remained unchanged. 8 - Mean zooplankton abundances were also reliable, distinguishing pristine stations (789 - 3,111 animals m -3 ) and highly eutrophic stations (114,970 – 563,339 animals m -3 ). 9 - The group ‘Larvae’ and the copepod Dioithona occulata were major contributors to mean abundances, since as small herbivores they are able to take advantage of high phytoplankton concentrations. 10 - Other taxa like Acartia tonsa and harpacticoid copepods were ubiquitous and although never numerically dominant showed high numbers at the more eutrophic sites. 11 - This makes relative abundances of cosmopolitan species as reliable an index as presence absence of key species in mangrove lagoons.

Mapping temperature distributions in flows using radiating high-porosity meshes

A technique to visualise and measure temperature distributions in gas flows is described which places fine, highly-emissive planar meshes in the heated flow and images them with an IR camera. Fine meshes with high porosity are used to minimise the disturbance to the flow field and ensure that the local mesh temperature is close to the local gas temperature. The radiation received by the camera is a function of both the temperature and the emissivity of the body visualised. In the case of a porous mesh, the camera will visualise both the mesh surface and the background through the mesh apertures. An effective emissivity, which combines the relative area fraction and emissivity of the mesh can be obtained via calibration. This effective emissivity is used to reduce the intensity data to temperature distributions. Attention must be paid to the ratio of the size of the projected camera pixel to the mesh opening size to ensure accuracy. The technique is demonstrated on a number of buoyant jet flows and the potential application of the technique to higher temperature flows is discussed.

Fluidized Bed Device for Plastic Granules Triboelectrification

The study of the triboelectrification process is the key factor to the successful industrial application of electrostatic separation in the field of plastics recycling. Therefore, the aim of the present work is to evaluate an original device for the laboratory study of this process. The original design of the fluidized bed type triboelectrification device has the following distinctive features: (i) transparent walls to observe the fluidization process and the particles moving in the triboelectrification module; (ii) air distributors with different mesh apertures correlated with granule size; (iii) quick replacement of the triboelectrification Plexiglas chamber with other metallic (aluminium, copper) or nonmetallic chambers (polyvinyl chloride—PVC, polyethylene—PE, and polyethylene terephthalate—PET); (iv) possibility of independent operation, for granule charge measurement or integrated operation, for the electrostatic separation experiments using a free-fall electrostatic separator. The results of charge measurement experiments pointed out the different triboelectric behaviour of two types of granules (polystyrene and low-density polyethylene) in contact with the walls of the device. The electrostatic separation experiments carried out on a binary mixture of mm-size polystyrene/polyethylene granules confirmed the effectiveness of the triboelectrification device.

Description and distribution of the larvae of two species of Fistulariidae (Teleostei, Syngnathiformes) in the southeastern Brazil

Fistulariidae contains the single genus, Fistularia, with four species. Two of these species are recorded from Brazil: Fistularia petimba and F. tabacaria. This study describes larvae of these two species of Fistularia, recording their distribution along the southeastern Brazilian coast, which is limited in the north by Real River (12° S) and in the south by São Tomé Cape (22° S). Samples were collected using a bongo net with mesh apertures of 330 and 500 µm during three oceanographic cruises conducted on spring/98 (Central III), winter/99 (Bahia 1) and autumn/00 (Central IV). The net was towed obliquely and the maximum depth was 200 m. Larvae of F. petimba were the most abundant and most widely distributed within the study area, including the seamounts of the Vitória-Trindade Ridge. Larvae of F. tabacaria were recorded only between 14° S and 21° S.

Accurate measurement of sputtered depth for ion sputtering rates and yields: the mesh replica method

AbstractFor the accurate measurements of crater depths, ion sputtering rates and ion sputtering yields in studies of sputter‐depth profiling using Auger electron spectroscopy (AES) or X‐ray photoelectron spectroscopy (XPS), a proposed mesh replica method has been evaluated. In this method, during ion sputtering, grids of between 50 and 400 mesh (per inch) are placed on the sample to retain unsputtered regions of the original surface to be used as reference. This enables a more accurate measurement of the depth to be made using a stylus profilometer close to the analytical region. The closer‐pitch meshes were thought to offer the prospect of measurements of higher accuracy. Calculations show that sputter deposits from the mesh sides may limit the mesh numbers used to 100 or those of a wider pitch for both stationary and rotated samples. A correlation with published data for stationary samples and new data for rotated samples confirms the calculations. In practice, it is difficult, without a special holder, to have intimate contact between the grid and sample. Such a holder is described. Further calculations concerning the shadowed profiles at the grid bar regions show that the grids may lift off the sample surface by 4–16 µm. This leads to non‐vertical crater walls in each mesh aperture. This effect, however, does not change the above conclusion on the mesh sizes to be used. In this range, the spurious appearance of Auger electrons emitted from the grid material is calculated to be less than 1%. This conclusion applies to the meshes evaluated here, which range in thickness from 13 to 29 µm. Thinner meshes may lead to the applicability of proportionately closer meshed grids in sputter‐profiling applications. Copyright © 2006 John Wiley & Sons, Ltd. The contribution of Martin P. Seah of the National Physical Laboratory is published with the permission of the Controller of HMSO and the Queen's Printer for Scotland.

Physical stability and aerosol properties of liposomes delivered using an air-jet nebulizer and a novel micropump device with large mesh apertures

The aerosol properties of liposomes and their physical stability to aerosolization were evaluated using an air-jet nebulizer (Pari LC Plus) and a customized large aperture vibrating-mesh nebulizer (Aeroneb Pro-8 μm). Soya phosphatidylcholine: cholesterol (1:1 mole ratio) multilamellar liposomes (MLVs) entrapping salbutamol sulfate were nebulized directly, or after being reduced in size by extrusion through 1 or 0.4 μm polycarbonate membrane filters. MLVs were very unstable to jet nebulization and stability was not markedly enhanced when vesicles were extruded before nebulization, such that drug losses from delivered liposomes using the Pari nebulizer were up to 88% (i.e. only 12% retained in liposomes). The Aeroneb Pro-8 μm nebulizer was less disruptive to liposomes, completed nebulization in a much shorter time, and produced greater mass output rate than the Pari nebulizer. However, aerosol droplets were larger, total drug and mass outputs were lower and aerosolization performance was dependent on formulation. Vibrating-mesh nebulization was less disruptive to liposomes extruded through the 1 μm membranes compared with the non-extruded MLVs, so that the retained entrapment of the drug in the nebulized vesicles was 56% and 37%, respectively. However, extrusion of liposomes to 0.4 μm resulted in reduced stability of liposomes to vibrating-mesh nebulization (retained entrapment = 41%) which was attributed to the reduced liposome lamellarity and subsequent reduced resistance to nebulization-induced shearing. This study has shown that vibrating-mesh nebulization using the customized large aperture mesh nebulizer (Aeroneb Pro-8 μm) had a less disruptive effect on liposomes and produced a higher output rate compared with the Pari LC Plus air-jet nebulizer. On the other hand, the air-jet nebulizer produced higher total mass and drug outputs and smaller aerosol droplets.

Suppression of two-spotted spider mite ( Tetranychus urticae), mealy bug ( Pseudococcus sp) and aphid ( Myzus persicae) populations and damage by vermicomposts

A vermicompost, produced commercially from food wastes, was tested for its capacity to suppress populations and damage to plants, by two-spotted spider mites ( Tetranychus urticae), mealy bugs ( Pseudococcus sp.) and aphids ( Myzus persicae), in the greenhouse. A range of mixtures of food waste vermicompost and a soil-less bedding plant growth medium Metro-Mix 360 (MM360) was tested in cages (40 cm × 40 cm × 40 cm) (0.2 mm mesh aperture) into which known numbers of greenhouse-bred pests were released. The crops tested were cucumbers and tomatoes for mealy bugs, bush beans and eggplants for spider mites, and cabbages for aphids. In all experiments, four 10 cm diameter pots, each containing one seedling, grown in the same MM360/vermicompost mixture were exposed to either 50 mealy bugs, 100 spider mites, or 100 aphids in cages, with each cage treatment replicated 4 times per treatment. The five growth mixtures tested were: (i) 100% MM360; (ii) 90% MM360 with 10% vermicompost; (iii) 80% MM360 with 20% vermicompost; (iv) 60% MM360 with 40% vermicompost; and (v) 20% MM360 with 80% vermicompost. Almost all of the mixtures containing vermicomposts suppressed the arthropod pest populations, and decreased pest damage significantly, compared with the MM360 controls. Not only did the vermicomposts make the plants less attractive to the pests, but they also had considerable effects on pest reproduction over time. The effects of the vermicompost substitutions tended to be least on spider mites, intermediate on mealy bugs, and greatest on aphids; however this may relate to the motility of the pests, as well as to the suppression potential of vermicomposts. Possible mechanisms for the suppression discussed include: the form of nitrogen available in the leaf tissues, the effects of vermicomposts on micronutrient availability, and the possible production of phenols, by the plants after applications of vermicomposts, making the tissues unpalatable.

APPLICATION OF PIXE FOR A MULTI-ELEMENT ANALYSIS OF MARINE PHYTOPLANKTON TOWARDS THE DEVELOPMENT OF A NEW BIOLOGICAL ASSESSMENT METHOD FOR HEAVY METAL POLLUTION

Particle-induced X-ray emission (PIXE) was applied for the determination of heavy metals accumulated in natural phytoplankton. We selected four Japanese marine sites to collect phytoplankton: Toni Bay and Kamaishi Bay (Kamaishi, Iwate) as non-polluted areas; and Shimotsu port (Shimotsu, Wakayama) and Toyama new port (Shinminato, Toyama) as polluted areas. After removing the zooplankton and visible dust by passing the seawater through an NXX13 plankton net (95-μm mesh aperture), the phytoplankton were collected on a polycarbonate filter (25 mm diameter, 1.0 μm pore size) by suction filtration. The filter was dried and subjected to scanning electron microscopy (SEM) and a PIXE analysis. The phytoplankton consisted of diatoms, dinoflagellates and coccolithophores were observed by SEM analysis on the filter prepared from 100 ml of Toni Bay seawater. Heavy metals ( Pb , Ni , Cu , Cr , Zn , Mn , Hg and As ) could be detected by the PIXE analysis in almost all the cases tested, in which 50-200 ml each of respective seawater sample was filtered. There was a linear relationship between the amount of heavy metals on the polycarbonate filter (ng cm-2) and the volume of seawater (25-200 ml) filtered (i.e. the amount of phytoplankton collected on the filter). Likewise, the PIXE analysis revealed that significant differences in heavy metal contamination between the polluted and non-polluted areas, and also among sampling sites in a polluted area depending on the location and seawater movement. These results indicate that a multi-element analysis of marine phytoplankton by PIXE would be a promising technique for biologically assessing and monitoring heavy metal pollution in the first link of the aquatic food chain.

Heat transfer enhancement in pool boiling of a refrigerant fluid with wire nets structures

Among many methods to enhance boiling heat transfer by means of porous coatings, the use of the wire nets covering the heated surface demonstrates some advantages due to its simplicity and low cost. Easiness of a wire net mounting at the heated wall allows testing many different nets and their combinations. This paper presents the experimental results on heat transfer and crisis using the dielectric refrigerant R141b pool boiling under atmospheric pressure. The analysis carried out in the present paper demonstrates that success in boiling heat transfer enhancement is provided not only by the nucleation sites density increase, but also by designing the channels in the porous structure to escape the generated vapor. Unsatisfactory results in relation to CHF value have been obtained with rather thick porous coating. In this case the problem is to provide vapor evacuation from the wall. Rather essential heat transfer coefficient and CHF increase has been observed while the porous structure has been formed with 3–7 layers of nets using wire of 0.25–0.40 mm diameter and mesh aperture of approximately 2 mm. The nets of stainless steel gave the greater effect with respect to copper, aluminium and brass. It is demonstrated that the presence of porous coatings brings about a considerable enhancement of the thermal stability of the system. An approximate model of crisis in boiling at the surface coated with metallic nets has been developed.

Leptocephali collected off the eastern coast of Brazil (12°–23°S)

Although leptocephali are very conspicuous in plankton samples little is known about their occurrence and distribution along the Brazilian coast. Therefore, the present study aimed to identify the leptocephali and their distribution pattern along the eastern Brazilian coast, which is limited in the north by Real River (12°S) and in the south by São Tomé Cape (23°S). Samples were collected during three oceanographic cruises conducted on October–December 1998, May–July 1999 and March–May 2000. Samplings were done using a bongo net with mesh apertures of 330 and 500 µm. The net was towed obliquely and the maximum depth was 200 m. A total of 13 families, 12 genera and 29 species of leptocephali were identified in the study area. Most taxa identified had already been recorded as adult, but the larval phase of some of them had not been identified for this region yet. Among them, Derichthyidae, Avocettina paucipora and Tiluropsis had not been recorded for this region either as adult or as larvae. Most taxa occurred mainly along the Bahia coast but some species were collected strictly in the southern region of the study area.

Improvement of Lighting Uniformity in Field Emission Display with Carbon Nano-Tube Cathodes

Lighting tubes using CNT printed cathodes for large-scale flat displays were fabricated and their fundamental characteristics such as brightness, drive voltage vs emission current under various types of CNT surface treatment, emission life and adjacent leakage of light are described. The brightness of 3000 cd/m2 was obtained with a 10 kV anode voltage and a 0.5 mA anode current. Though there are many CNTs, which are not aligned vertically to the gate electrode, in the cathodes, uniformity of pixel light is not sufficient and filamentary concentration of light is observed. We provided a shield electrode with special mesh aperture between the gate electrodes and an anode in order to improve the uniformity of light. As a result, we can obtain nearly uniform pixel light with a much lower shield electrode voltage than the gate electrodes.

Changes to regulations and the gear used in the South African commercial fishery for Jasus lalandii

Alterations to the operational fishing gear used in the South African west coast rock lobster Jasus lalandii fishery and their resultant impacts are investigated. The most important developments have been: (i) a change during the 1960s from hand-hauled hoopnets to winch-hauled traps, with a concomitant modification of vessels; (ii) the introduction of deck-grid sorters in 1975; (iii) an increase during 1984 of minimum mesh aperture from 62 to 100 mm (stretched), with a concomitant decrease in the length of the trap codend; (iv) a decrease in the minimum legal size during the early 1990s; and (v) the introduction of bottom-grid traps in 1994. Most of these alterations have been driven by a trade off between the need for greater operational efficiency and concerns surrounding the issue of how best to deal with the problem of catching and releasing specimens smaller than the minimum legal size.

Transfer of organic matter in the deep Arabian Sea zooplankton community: insights from δ15N analysis

Zooplankton samples were obtained in the central Arabian Sea using a 1 m 2 -MOCNESS with 333 μm mesh aperture to investigate the nitrogen stable isotopic composition of different mesozooplankton size classes (<0.5, 0.5–1, 1–2, 2–5 mm) from the surface down to 3900 m depth in intervals of ⩽500 m during April 1997 and February 1998. Samples from the upper 500 m indicated temporal differences between two years, with the lowest value (4.5 ‰) for the 1–2 mm size class between 250 and 500 m depth in April 1997 and the highest value (13.5 ‰) for the 2–5 mm size class in the same depths range in February 1998. The upper bathypelagic zone (1000–2500 m) showed an increase in δ 15N with increasing depth for all size classes. In April 1997, the size-dependent distribution showed higher values in the larger size classes, indicating higher trophic levels as compared to smaller size classes. Such a size-dependent increase was not evident in February 1998. Below 2500 m, the δ 15N values were more or less stable with increasing depth, or even decreased as exemplified by the smallest size class (<0.5 mm) . The size-dependent distribution for both investigated periods showed increasing δ 15N values with increasing size. These results give an insight in the trophic structure of the zooplankton community in the deep Arabian Sea. Differences between size classes were less than one trophic level in the upper bathypelagic zone (1000–2500 m) and one to two trophic levels in the lower bathypelagic zone (>2500 m) . The amount of diet needed by the different mesozooplankton size classes to build up the measured biomass is estimated for the deep bathypelagic zone.

Species Composition, Distribution and Abundance of Hydromedusae in the Exclusive Economic Zone of the East Coast of India

Based on zooplankton collections made by Fisheries Ocean Research Vessel Sagar Sampada Central Marine Fisheries Research Institute, India, during the period 1986-1990, 356 samples from 18 cruises from Sri Lanka to Calcutta coast were analysed. The hydromedusae were encountered in 273 samples and more than 62 species were found. Liriope tetraphylla dominated in the percentage of occurrence and population density. Aglaura hemistoma, Solmundella bitentaculata, Rhopalonema velatum, Cytaeis tetrastyla, Bougainvillia fulva and Phialidium hemisphaericum were the commonly occurring species. The maximum species diversity was noticed away from the nearshore stations, while maximum population density was from nearshore stations. reported by Navas (1971), Vannucci and Navas (1973a, b, c) and Santhakumari (1977a) based on the samples in the International Indian Ocean Expedition (1962-1965). But in this expedition coastal areas were not thoroughly sampled. A comprehensive study from the coast of India, especially in its exclusive economic zone (EEZ), has not been undertaken. The available information on the distribution of hydromedusae is confined to areas off the southwest coast of India (Nair, 1954; Vannucci and Santhakumari, 1969; Santhakumari, 1977a, b, 1991). The only a report about the destribution of hydromedusae from the east coast of India is by Ganapati and Nagabhushanam (1958) who recorded the seasonal distribution of hydromedusae from Visakhapatnam. The present paper deals with the distribution of hydromedusae based on the material collected by FOR V Sagar Sampada from the EEZ of the east coast of India. Materials and Methods Samples were collected in 18 cruises on board FORV Sagar Sampada from the EEZ of the east coast of India, from Sri Lanka to Calcutta, during the period 1986-1990. By an oblique haul from 150m depth to surface using Bongo net (mouth diameter 60 em; mesh aperture 0.33 mm) equipped with a calibrated flow meter, 356 zooplankton samples were taken and preserved in 5% formalin sea water solution, and the hydromedusae were separated and analysed. The sampling details were presented in the cruise reports (Central Marine Fisheries Research Institute, 1986). Hydromedusae counts were transformed to numbers per unit volume using flow meter data.

Following the decomposition of ryegrass labelled with 13C and 15N in soil by solid‐state nuclear magnetic resonance spectroscopy

SummaryInvestigating the biogeochemistry of plant material decomposition in soil has been restricted by difficulties extracting and identifying organic compounds. In this study the decomposition of 13C‐ and 15N‐labelled Lolium perenne leaves mixed with mineral soil has been investigated over 224 days of incubation under laboratory conditions. Decomposition was followed using short‐term rates of CO2 evolution, the amounts of 13C and 15N remaining were determined by mass spectrometry, and 13C and 15N solid‐state nuclear magnetic resonance (NMR) spectroscopy was used to characterize chemically the plant material as it decomposed. After 224 days 48% of the added 13C had been lost with a rapid period of C02 evolution over the first 56 days. The fraction of cross‐polarization magic angle spinning (CP MAS) 13C NMR spectra represented by O‐alkyl‐C signal probably in carbohydrates (chemical shift, 60–90 p.p.m.) declined from 60 to 20% of the spectrum (chemical shift, 0–200 p.p.m.) over 224 days. The rate of decline of the total 13C exceeded that of the 60–90 p.p.m. signal during the first 56 days and was similar thereafter. The fraction of the CP MAS 13C NMR spectra represented by the alkyl‐ and methyl‐C (chemical shift, 10–45 p.p.m.) signal increased from 5 to 14% over the first 14 days and was 19% after 224 days. CP MAS 13C NMR of 13C‐ and 15N‐L. perenne contained in 100‐μm aperture mesh bags incubated in the soil for 56 days indicated that the remaining material was mainly carbohydrate but there was an increase in the alkyl‐ and methyl‐C associated with the bag's contents. After 224 days incubation of the labelled 13C‐ and 15N‐L. perenne mixed with the soil, 40% of the added N had been lost. Throughout the incubation there was only one signal centred around 100 p.p.m. detectable in the CP MAS 15N NMR spectra. This signal corresponded to amide 15N in peptides and may have been of plant or microbial origin or both. Although there had been substantial interaction between the added 15N and the soil microorganisms, the associated redistribution of 15N from plant to microbial tissues occurred within the amide region. The feasibility of following some of the component processes of plant material decomposition in soil using NMR has been demonstrated in this study and evidence that microbial synthesis contributes to the increase in alkyl‐ and methyl‐C content of soil during decomposition has been represented.

How sieve mesh size affects sample estimates of estuarine benthic macrofauna

The way mesh size influences the reliability of density and biomass estimates in macrofauna sampling was investigated for a benthic community in the shallow, upper reaches of a small, temperate estuary. Macrofauna was separated from the sediment with sieves of 0.25, 0.5 and 1.0 mm mesh aperture size and the performance of each gear type in terms of retention efficiency evaluated. The 0.25 mm sieve sampled all macrofauna adequately, but only 55% of all individuals were, on average, retained by the 0.5 mm mesh and a mere 8% by the 1.0 mm mesh. Mean retention efficiency for total biomass was 86% for the 0.5 mm and 49% for the 1.0 mm screen, respectively. Undersampling by bigger mesh sizes was most severe for juveniles and small species, resulting in biased interpretation of apparent community structure. Because population densities obtained by the two bigger screens were not only markedly less accurate (i.e., biased lower counts), but also less precise (i.e., higher standard errors), the use of 0.5 mm and 1.0 mm mesh sizes significantly increased replication levels. Consequently, for this specific habitat and community, sampling schemes which employ a 1.0 mm mesh were considerably more expensive than designs using finer screens. No single sampling design will perform optimally in each permutation of habitat and community, but our data emphasise the need for the stringent assessment of sampling errors and caution against the uncritical use of mesh sizes greater than 0.25 mm in estimating population densities of estuarine macrobenthos.

Mesh size selection and diel variability in catch of fish traps on the central Great Barrier Reef, Australia: a preliminary investigation

The effect of mesh size and diel variability in fish trap catch was investigated on the central Great Barrier Reef in order to select an optimal mesh size for ecological studies of lutjanids (snappers) and lethrinids (emperors). Four mesh sizes, 12.5 mm square, 30 mm hexagonal, 40 mm hexagonal and 50 mm hexagonal were examined over two sampling periods (day versus night) yielding a total of 1571 fish representing 70 species from 451 trap hauls. Mesh size had no significant effect on the total catch rate of fish traps. The 40 mm hexagonal mesh size was, however, the preferred mesh size because the size range of target species ( Lutjanus and Lethrinus) caught in this mesh was greater than that in the 50 mm hexagonal mesh and the mean catch rate tended to be greater than the 30 mm hexagonal mesh. The mean catch rate in the 12.5 mm square mesh was low relative to the mean catch rates of the other mesh sizes tested and the size range of target species caught in the mesh size were not significantly different from that caught in the 30 mm hexagonal mesh. Diel sampling period had a significant effect on the catch of fish traps. More fish were captured at night, with the lutjanids (78% of total catch) and lethrinids dominating night and day catches, respectively. Mesh selectivity in fish traps was probably not a simple function of the ability of a given mesh aperture to retain individuals of a certain body depth. The behaviour and activity patterns of reef fish in response to the visual outline of the traps was considered of prime importance in the mesh selectivity.

A planar two-dimensional circular aperture metal grating coupler for quantum well infrared photodetectors

A numerical analysis of the grating coupling for a two-dimensional circular aperture mesh metal grating coupled GaAs quantum well infrared photodetector (QWIP) has been carried out. The inner products of Floquet modes and waveguide modes were derived in a simple analytic form. Using the normalized wavelength and normalized aperture radius, two sets of universal plots were generated to display the normalized total power and absorption angle of the higher-order diffracted waves versus normalized wavelength for the grating coupler. From these universal plots, the optimum grating parameters for the GaAs QWIPs can be obtained. The results show a 2.7 times enhancement of the responsivity at 10.2 μm wavelength for the circular aperture metal grating coupler over that of the 45° edge-illuminated GaAs QWIP.

The signal transmission characteristics of embedded microstrip transmission lines over a meshed ground plane in copper/polyimide multichip module

The high-speed digital signal transmission characteristics of a microstrip transmission line in a meshed ground plane environment were studied. It is found that ground plane geometry significantly affects the degree of crosstalk noise between two adjacent signal lines and the characteristic impedance of a transmission line. A signal conductor over a meshed ground plane exhibits less degradation in rise time and voltage amplitude, compared to a line over a solid ground plane, due to the lower line capacitance and lower conductor loss. However, the longer current path in the case of a meshed ground plane increases the overall line inductance which results in a slower propagation velocity. A ground plane with optimum geometric configuration, in mesh pitch and aperture, is chosen that meets system level performance requirements while still being compatible with processing constraints. The impact of transmission lines with meshed ground plane on multichip module design for digital applications is also discussed. >

An in vitro assay utilising parasitic larval Haemonchus contortus to detect resistance to closantel and other anthelmintics

Rothwell J. T. and Sangster N. C. 1993. An in vitro assay utilising parasitic larval Haemonchus contortus to detect resistance to closantel and other anthelmintics. International Journal for Parasitology 23: 573–578. A new assay for detecting resistance to anthelmintics in vitro is described. The assay uses a simple culture system in which the ability of anthelmintics to kill or inhibit the migration of parasitic third and fourth stage Haemonchus contortus larvae through a 50 μm aperture mesh is assessed. The assay detects 2–10-fold resistance to closantel. Resistance to benzimidazoles, levamisole and ivermectin can also be detected.