Modelling the activated sludge flocculation process combining laser light diffraction particle sizing and population balance modelling (PBM)

A technique based on laser light diffraction is shown to be successful in collecting on-line experimental data. Time series of floc size distributions (FSD) under different shear rates (G) and calcium additions were collected. The steady state mass mean diameter decreased with increasing shear rate G and increased when calcium additions exceeded 8 mg/l. A so-called population balance model (PBM) was used to describe the experimental data, This kind of model describes both aggregation and breakage through birth and death terms. A discretised PBM was used since analytical solutions of the integro-partial differential equations are non-existing. Despite the complexity of the model, only 2 parameters need to be estimated: the aggregation rate and the breakage rate. The model seems, however, to lack flexibility. Also, the description of the floc size distribution (FSD) in time is not accurate.

Spatial distribution of vectors of Ross River virus and Barmah Forest virus on Russell Island, Moreton Bay, Queensland

We used a network of 20 carbon dioxide- and octenol-supplemented light traps to sample adult mosquitoes throughout Russell Island in southern Moreton Bay, south-east Queensland. Between February and April 2001, an estimated 1365 564 adult female mosquitoes were collected. In contrast to an average catch of 9754 female mosquitoes per trap night on Russell Island, reference traps set on Macleay Island and on the mainland returned average catches of 3172 and 222, respectively. On Russell Island, Ochlerotatus vigilax (Skuse), Coquillettidia linealis (Skuse), Culex annulirostris Skuse and Verrallina funerea (Theobald), known or suspected vectors of Ross River (RR) and/or Barmah Forest (BF) viruses, comprised 89.6% of the 25 taxa collected. When the spatial distributions of the above species were mapped and analysed using local spatial statistics, all were found to be present in highest numbers towards the southern end of the island during most of the 7 weeks. This indicated the presence of more suitable adult harbourage sites and/or suboptimal larval control efficacy. As immature stages and the breeding habitat of Cq. linealis are as yet undescribed, this species in particular presents a considerable impediment to proposed development scenarios. The method presented here of mapping the numbers of mosquitoes throughout a local government area allows specific areas that have high vector numbers to be defined.

Light and electron microscopic analysis of aquaporin 1-like-immunoreactive amacrine cells in the rat retina

Aquaporin 1 (AQP1; also known as CHIP, a channel-forming integral membrane protein of 28 kDa) is the first protein to be shown to function as a water channel and has been recently shown to be present in the rat retina. We previously showed (Kim et al. [1998] Neurosci Lett 244:52-54) that AQP1-like immunoreactivity is present in a certain population of amacrine cells in the rat retina. This study was conducted to characterize these cells in more detail, With immunocytochemistry using specific antisera against AQP1, whole-mount preparations and 50-mum-thick vibratome sections were examined by light and electron microscopy. These cells were a class of amacrine cells, which had symmetric bistratified dendritic trees ramified in stratum 2 and in the border of strata 3 and 4 of the inner plexiform layer (IPL). Their dendritic field diameters ranged from 90 to 230 mum. Double labeling with antisera against AQP1 and gamma-aminobutyric acid or glycine demonstrated that these AQP1-like-immunoreactive amacrine cells were immunoreactive for glycine. Their most frequent synaptic input was from other amacrine cell processes in both sublaminae a and b of the IPL, followed by a few cone bipolar cells. Their primary targets were other amacrine cells and ganglion cells in both sublaminae a and b of the IPL. In addition, synaptic output Onto bipolar cells was rarely observed in sublamina b of the IPL. Thus, the AQP1 antibody labels a class of glycinergic amacrine cells with small to medium-sized dendritic fields in the rat retina. (C) 2002 Wiley-Liss, Inc.

Photosynthetic light and temperature responses of Eucalyptus cloeziana and Eucalyptus argophloia

Acclimation of gas exchange to temperature and light was determined in 18-month-old plants of humid coastal (Gympie) and dry inland ( Hungry Hills) provenances of Eucalyptus cloeziana F. Muell., and in those of a dry inland provenance of Eucalyptus argophloia Blakely. Plants were acclimated at day/night temperatures of 18/13, 23/18, 28/23 and 33/ 28 degreesC in controlled-temperature glasshouses for 4 months. Light and temperature response curves were measured at the beginning and end of the acclimation period. There were no significant differences in the shape and quantum-yield parameters among provenances at 23, 28 and 33 degreesC day temperatures. Quantum yield [mumol CO2 mumol(- 1) photosynthetic photon flux density (PPFD)] ranged from 0.04 to 0.06 and the light response shape parameter ranged from 0.53 to 0.78. Similarly, no consistent trends in the rate of dark respiration for plants of each provenance were identified at the four growth temperatures. Average values of dark respiration for the plants of the three provenances ranged from 0.61 to 1.86 mumol m(-2) s(-1). The optimum temperatures for net photosynthesis increased from 23 to 32 degreesC for the humid- and from 25 to 33 degreesC for the dry-provenance E. cloeziana and from 21 to 33 degreesC for E. argophloia as daytime temperature of the growth environment increased from 18 to 33 degreesC. These results have implications in predicting survival and productivity of E. cloeziana and E. argophloia in areas outside their natural distribution.

Movements of the ricefield rat, Rattus argentiventer, near a trap-barrier system in rice crops in West Java, Indonesia

The movements of the ricefield rats (Rattus argentiventer) near a trap-barrier system (TBS) were assessed in lowland flood-irrigated rice crops in West Java, Indonesia, to test the hypothesis that a TBS with a 'trap-crop' modifies the movements of rats within 200 m from the trap-crop. The home range use and locations of rat burrows were assessed using radiotelemetry at two sites, one with a TBS with trap-crop (Treatment site, the crop inside the fence was planted 3 weeks earlier than the surrounding crop) and the other with a TBS without trap-crop (Control site, the crop inside the fence was planted at the same time as the surrounding crop). Each TBS was a 50 x 50 m plastic fence with eight multiple-capture rat traps set at the base. More than 700 rats were caught in the TBS with trap-crop, whereas only 10 rats were caught in the TBS without trap-crop. The home range size of females was significantly smaller at the Treatment site (0.96 ha) than the Control site (2.99 ha), but there was no difference for males. Seventy-eight per cent of rats caught in the TBS and fitted with radiocollars had their daytime burrow locations within 200 m of the TBS. We could not determine if the rats caught in the TBS were residents or transients according to demographic parameters. Our results support the hypothesis that a TBS with a trap-crop protects the surrounding rice crop out to a distance of at least 200 m.

Occlusable corneas in toadfishes: light transmission, movement and ultrastruture of pigment during light- and dark-adaptation

The toadfishes Tetractenos hamiltoni and Torquigener pleurogramma (Tetraodontidae) possess occlusable yellow corneas. We examine the light transmission and location of the yellow/orange pigment throughout the cornea, the temporal properties of pigment migration and the ultrastructure of the pigmented processes during light- and dark-adaptation. Each species was dark-adapted during the day and light-adapted during the night and then exposed to either sun illumination or darkness for different lengths of time (0-70 min). Movement of corneal pigment could be induced in both species regardless of time of day or night. The pigment was able to migrate in a dorsal or ventral direction and changed from minimal to maximal pigmentation within 60 min. Three types of transmission curves were found with varying degrees of transmission in the 400-500 nm waveband, indicating that the pigment distribution is not uniform across the cornea; some areas of the cornea transmit near UV light, while others absorb blue light. The gradual change of the transmission characteristics in different areas of the cornea indicates the presence of different concentrations of a single type of pigment. Ultrastructural examination of the corneas showed that the layer containing the pigment is situated within the scleral cornea either surrounding (T. pleurogramma) or abutting (T. hamiltoni) an iridescent layer. Long sheet-like processes or chromatophores extending centrally from dorsal and ventral reservoirs are filled with pigment during the light-adapted state but empty in the dark-adapted state.

Field evaluation of a sentinel mosquito (Diptera : culicidae) trap system to detect Japanese encephalitis in remote Australia

Incursions of Japanese encephalitis (JE) virus into northern Queensland are currently monitored using sentinel pigs. However, the maintenance of these pigs is expensive, and because pigs are the major amplifying hosts of the virus, they may contribute to JE transmission. Therefore, we evaluated a mosquito-based detection system to potentially replace the sentinel pigs. Single, inactivated JE-infected Culex annulirostris Skuse and C. sitiens Wiedemann were placed into pools of uninfected mosquitoes that were housed in a Mosquito Magnet Pro (MM) trap set under wet season field conditions in Cairns, Queensland for 0, 7, or 14 d. JE viral RNA was detected (cycling threshold [CT] = 40) in 11/ 12, 10/14, and 2/5 pools containing 200, 1,000, and 5,000 mosquitoes, respectively, using a TaqMan real-time reverse transcription-polymerase chain reaction (RT-PCR). The ability to detect virus was not affected by the length of time pools were maintained under field conditions, although the CT score tended to increase with field exposure time. Furthermore, JE viral RNA was detected in three pools of 1,000 mosquitoes collected from Badu Island using a MM trap. These results indicated that a mosquito trap system employing self-powered traps, such as the MosquitoMagnet, and a real-time PCR system, could be used to monitor for JE in remote areas.

Retinal specializations in the blue marlin: eyes designed for sensitivity to low light levels

The large eyes and well-developed visual system of billfishes suggest that vision is an important sense for the detection and interception of prey and lures. Investigations of visual abilities in these large pelagic fishes are difficult, however anatomical studies of billfish eyes and retinas allow prediction of a number of visual capabilities. From the density of ganglion cells in the blue marlin (Makaira nigricans) retina, visual acuities of less than 10 cycles per degree were derived, a surprisingly low visual resolution given the absolute size of the marlin eye. Cone photoreceptors, on the other hand, were present in high densities, resulting in a presumed summation of cones to ganglion cells at a ratio of 40:1, even in the area of best vision. The optical sensitivity of the marlin eye was high owing to the large dimensions of the cone photoreceptors. These results indicate that the marlin eye is specifically adapted to cope with the low light levels encountered during diving. Since the marlin is likely to use its vision at depth, it is suggested that this line of research could help estimate the limits of vertical distribution based on light level.

Visual Biology of Hawaiian Coral Reef Fishes. III. Environmental Light and an Integrated Approach to the Ecology of Reef Fish Vision

In the previous two papers in this three-part series, we have examined visual pigments, ocular media transmission, and colors of the coral reef fish of Hawaii. This paper first details aspects of the light field and background colors at the microhabitat level on Hawaiian reefs and does so from the perspective and scale of fish living on the reef. Second, information from all three papers is combined in an attempt to examine trends in the visual ecology of reef inhabitants. Our goal is to begin to see fish the way they appear to other fish. Observations resulting from the combination of results in all three papers include the following. Yellow and blue colors on their own are strikingly well matched to backgrounds on the reef such as coral and bodies of horizontally viewed water. These colors, therefore, depending on context, may be important in camouflage as well as conspicuousness. The spectral characteristics of fish colors are correlated to the known spectral sensitivities in reef fish single cones and are tuned for maximum signal reliability when viewed against known backgrounds. The optimal positions of spectral sensitivity in a modeled dichromatic visual system are generally close to the sensitivities known for reef fish. Models also predict that both UV-sensitive and red-sensitive cone types are advantageous for a variety of tasks. UV-sensitive cones are known in some reef fish, red-sensitive cones have yet to be found. Labroid colors, which appear green or blue to us, may he matched to the far-red component of chlorophyll reflectance for camouflage. Red cave/hole dwelling reef fish are relatively poorly matched to the background they are often viewed against but this may be visually irrelevant. The model predicts that the task of distinguishing green algae from coral is optimized with a relatively long wavelength visual pigment pair. Herbivorous grazers whose visual pigments are known possess the longest sensitivities so far found. Labroid complex colors are highly contrasting complementary colors close up but combine, because of the spatial addition, which results from low visual resolution, at distance, to match background water colors remarkably well. Therefore, they are effective for simultaneous communication and camouflage.

Alternatively spliced products of the human kinesin light chain 1 (KNS2) gene

Conventional kinesin is a microtubule-based molecular motor involved in the transport of membranous and non-membranous cargoes. The kinesin holoenzyme exists as a heterotetramer, consisting of two heavy chain and two light chain subunits. It is thought that one function of the light chains is to interact with the cargo. Alternative splicing of kinesin light chain pre-mRNA has been observed in lower organisms, although evidence for alternative splicing of the human gene has not been reported. We have identified 19 variants of the human KNS2 gene (KLC1) that are generated by alternative splicing of downstream exons, but calculate that KNS2 has the potential to produce 285919 spliceforms. Corresponding spliceforms of the mouse KLC1 gene were also identified. The alternative exons are all located 3' of exon 12 and the novel spliceforms produce both alternative carboxy termini and alternative 3' untranslated regions. The observation of multiple light chain isoforms is consistent with their proposed role in specific cargo attachment.

Effects of mercury on the arterial blood pressure of anesthetized rats

The available data suggests that hypotension caused by Hg2+ administration may be produced by a reduction of cardiac contractility or by cholinergic mechanisms. The hemodynamic effects of an intravenous injection of HgCl2 (5 mg/kg) were studied in anesthetized rats (N = 12) by monitoring left and right ventricular (LV and RV) systolic and diastolic pressures for 120 min. After HgCl2 administration the LV systolic pressure decreased only after 40 min (99 ± 3.3 to 85 ± 8.8 mmHg at 80 min). However, RV systolic pressure increased, initially slowly but faster after 30 min (25 ± 1.8 to 42 ± 1.6 mmHg at 80 min). Both right and left diastolic pressures increased after HgCl2 treatment, suggesting the development of diastolic ventricular dysfunction. Since HgCl2 could be increasing pulmonary vascular resistance, isolated lungs (N = 10) were perfused for 80 min with Krebs solution (continuous flow of 10 ml/min) containing or not 5 µM HgCl2. A continuous increase in pulmonary vascular resistance was observed, suggesting the direct effect of Hg2+ on the pulmonary vessels (12 ± 0.4 to 29 ± 3.2 mmHg at 30 min). To examine the interactions of Hg2+ and changes in cholinergic activity we analyzed the effects of acetylcholine (Ach) on mean arterial blood pressure (ABP) in anesthetized rats (N = 9) before and after Hg2+ treatment (5 mg/kg). Using the same amount and route used to study the hemodynamic effects we also examined the effects of Hg2+ administration on heart and plasma cholinesterase activity (N = 10). The in vivo hypotensive response to Ach (0.035 to 10.5 µg) was reduced after Hg2+ treatment. Cholinesterase activity (µM h-1 mg protein-1) increased in heart and plasma (32 and 65%, respectively) after Hg2+ treatment. In conclusion, the reduction in ABP produced by Hg2+ is not dependent on a putative increase in cholinergic activity. HgCl2 mainly affects cardiac function. The increased pulmonary vascular resistance and cardiac failure due to diastolic dysfunction of both ventricles are factors that might contribute to the reduction of cardiac output and the fall in arterial pressure.

The influence of light spectra, UV-A, and growth regulators on the in vitro seed germination of Senecio cineraria DC.

This study was carried out to investigate the effects of light spectra, additional UV-A, and different growth regulators on the in vitro germination of Senecio cineraria DC. Seeds were surface-sterilized and inoculated in MS medium to evaluate the following light spectra: white, white plus UV-A, blue, green, red or darkness. The maximum germinability was obtained using MS0 medium under white light (30%) and MS + 0.3 mg L-1 GA3 in the absence of light (30.5%). S. cineraria seeds were indifferent to light. Blue and green lights inhibited germination. Different concentrations of gibberellic acid (GA3) (0.1; 0.4; 0.6; 0.8; 1.0 and 2.0 mg L-1) and indole-3-acetic acid IAA (0.1; 0.3 and 1.0 mg L-1) were evaluated under white light and darkness. No concentration of GA3 enhanced seed germination percentage under white light. However, when the seeds were maintained in darkness, GA3 improved germination responses in all tested concentrations, except at 1.0 mg L-1. Under white light, these concentrations also increased the germination time and reduced germination rate. Germination rate, under light or darkness, was lower using IAA compared with GA3.