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Sampling Period (sampling + period)
Selected AbstractsUse of monoclonal antibodies to quantify the dynamics of ,-galactosidase and endo-1,4-,-glucanase production by Trichoderma hamatum during saprotrophic growth and sporulation in peatENVIRONMENTAL MICROBIOLOGY, Issue 5 2005Christopher R. Thornton Summary Trichoderma species are ubiquitous soil and peat-borne saprotrophs that have received enormous scientific interest as biocontrol agents of plant diseases caused by destructive root pathogens. Mechanisms of biocontrol such as antibiosis and hyperparasitism are well documented and the biochemistry and molecular genetics of these processes defined. An aspect of biocontrol that has received little attention is the ability of Trichoderma species to compete for nutrients in their natural environments. Trichoderma species are efficient producers of polysaccharide-degrading enzymes that enable them to colonize organic matter thereby preventing the saprotrophic spread of plant pathogens. This study details the use of monoclonal antibodies (mAbs) to quantify the production of two enzymes implicated in the saprotrophic growth of Trichoderma species in peat. Using mAbs specific to the hemicellulase enzyme ,-galactosidase (AGL) and the cellulase enzyme endo-1,4-,-glucanase (EG), the relationship between the saprotrophic growth dynamics of a biocontrol strain of Trichoderma hamatum and the concomitant production of these enzymes in peat-based microcosms was studied. Enzyme activity assays and enzyme protein concentrations derived by enzyme-linked immunosorbent assay (ELISA) established the precision and sensitivity of mAb-based assays in quantifying enzyme production during active growth of the fungus. Trends in enzyme activities and protein concentrations were similar for both enzymes, during a 21-day sampling period in which active growth and sporulation of the fungus in peat was quantified using an independent mAb-based assay. There was a sharp increase in active biomass of T. hamatum 3 days after inoculation of microcosms with phialoconidia. After 3 days there was a rapid decline in active biomass which coincided with sporulation of the fungus. A similar trend was witnessed with EG activities and concentrations. This showed that EG production related directly to active growth of the fungus. The trend was not found, however, with AGL. There was a rapid increase in enzyme activities and protein concentrations on day 3, after which they remained static. The reason for the maintenance of elevated AGL probably resulted from secretion of the enzyme from conidia and chlamydospores. ELISA, immunofluoresence and immunogold electron microscopy studies of these cells showed that the enzyme is localized within the cytoplasm and is secreted extracellularly into the surrounding environment. It is postulated that release of oligosaccharides from polymeric hemicellulose by the constitutive spore-bound enzyme leads to AGL induction and could act as an environmental cue for spore germination. [source] Seasonal evaluation of reproductive status and exposure to environmental estrogens in hornyhead turbot at the municipal wastewater outfall of Orange County, CAENVIRONMENTAL TOXICOLOGY, Issue 5 2007Xin Deng Abstract Seasonal changes in developmental stages, condition factor (CF), gonadosomatic index, and plasma vitellogenin (Vtg) concentrations in male and female hornyhead turbot were examined at the wastewater outfall (T1) of the Orange County Sanitation District, and two farfield sites T11 (7.7 km northwest of the outfall) and Dana Point (35 km south of the outfall) between February 2005 and May 2006. Fish collected from the three sites exhibited male-oriented sex ratios. With few exceptions, developmental stages, CF, and GSI of both genders and plasma Vtg concentrations of females were not significantly different in samples collected from different sites at the same sampling period. More advanced gonad developmental stages and higher plasma Vtg concentrations in females were observed in August, indicating the seasonality of the reproductive cycle for this species. Plasma Vtg concentrations in males were observed in all of the sampling sites with the highest prevalence at T11 relative to T1 and Dana Point. The Vtg expression in males from the three sampling sites indicated widespread exposure to estrogenic compounds in waters of coastal California. However, the histopathological and reproductive relevance of the responses appeared to be insignificant and may not affect the population in these locations. © 2007 Wiley Periodicals, Inc. Environ Toxicol 22: 464,471, 2007. [source] Genetic diversity of the toxic cyanobacterium Microcystis in Lake MikataENVIRONMENTAL TOXICOLOGY, Issue 3 2005Mitsuhiro Yoshida Abstract The aim of the present study was to clarify the bloom dynamics and community composition of hepatotoxin microcystin-producing and non-microcystin-producing Microcystis genotypes in the environment. In Lake Mikata (Fukui, Japan) from April 2003 to January 2004, seasonal variation in the number of cells with microcystin (mcy) genotypes and the genetic diversity of the total population were investigated using quantitative competitive PCR and a 16S rDNA clone library, respectively. Using competitive PCR, cells with mcyA genotypes were quantified in August and October, and the ratio of the number of these mcyA genotypes to colony-forming Microcystis cells was 0.37 and 2.37, respectively. The 16S rDNA clones obtained could be divided into 12 ribotypes: a,l. Sixty-one Microcystis strains isolated from Lake Mikata during the sampling period were subjected to toxicity tests using HPLC and ELISA, PCR-based detection of the mcyA gene, and sequence analysis of the 16S rDNA. All isolates could be differentiated into 11 ribotypes (a, b, d, f, h, i, and m,q). Ribotypes b, f, i, m, n, and p had at least one strain that was a microcystin producer. In natural communities ribotypes b and f accounted for 85% of the 16S rDNA clones in August, and ribotypes b and i accounted for 24% of the clones in October. Thus, in some bloom stages the presence of microcystin genotypes identified using the 16S rDNA clone library correlated with that of mcy genotypes determined using competitive PCR. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 229,234, 2005. [source] Fluoride concentrations in antler bone of roe deer (Capreolus capreolus) indicate decreasing fluoride pollution in an industrialized area of western GermanyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2001Uwe Kierdorf Abstract In order to reconstruct temporal changes in ambient fluoride levels in the industrialized Ruhr area (western Germany), we analyzed the bone fluoride content of 167 antlers of roe deer (Capreolus capreolus) killed between 1951 and 1999 in the northern part of this region. Individual values ranged between 110 and 8,178 mg F,/kg ash, and there was an overall marked decrease over the sampling period. Average bone fluoride concentrations in antlers from the periods 1980 through 1989 (geometric mean [95% confidence interval]: 1,490 [1,193,1,861] mg/kg ash) and 1990 through 1999 (753 [644,882] mg/kg ash) differed significantly (p < 0.001) and were both significantly (p < 0.001) lower than those from the periods 1951 through 1969 (3,720 [3,227,4,288] mg/kg ash) and 1970 through 1979 (2,573 [2,203,3,006] mg/kg ash). The findings are seen as indicative of a progressively reduced atmospheric fluoride deposition into the study area, caused by effective emission-control measures in Germany and neighboring countries. Because antlers are replaced annually, grow during a fixed period of some months, and are regularly collected and kept as trophies, they are well suited as monitoring units for analyzing temporal trends in environmental pollution by fluoride and other bone-seeking pollutants. [source] Generalised algorithm of novel space vector modulation: for N -level three-phase voltage source inverterEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2008Hachemi Chekireb Abstract This paper concerns the development of a generalised algorithm of a novel space vector modulation (SVM) for N -level three-phase voltage source inverter. It is considering that the (N,1) DC input voltages of inverter are constant. The proposed method ensures initially the determination of the N3 inverter switching states, the extraction of the redundancies to obtain 3N(N -1),+,1 independent switching states and their organisation by sector in six distinct matrices Wk with k,=,(1,,,,,6). After that, these matrices Wk with k,=,(2,,,,,6) are ordered as the matrix W1 related to the first sector. So, the research of the three closest vectors to the reference vector is carried out only in first sector and for this purpose, the equivalent reference vector is introduced which is resulting from the rotation by ,(k,1),/3 of the reference vector. The on-line choice of the three vectors (three switching states of the inverter) is based on the distances between the equivalent reference vector and some vectors located in its vicinity in the (,,,) plane of the first sector. Moreover, a simple method for the calculation of the duty cycles for these three switching states is proposed which exploits directly the three shortest distances associated to these three selected vectors. The sequence of these three switching states over a sampling period is investigated in view to reduce the harmonic contents of the voltage output. The application is carried out on an N -level three-phase voltage source inverter, where N is an arbitrary odd integer. Finally, the phase voltage and its harmonic spectrum provided by a three-phase N- level inverter with N,=,(3,5,7,9,13,15) are presented to confirm the generalisation of this method. Copyright © 2007 John Wiley & Sons, Ltd. [source] Land-use influences macroinvertebrate community response following a pulse disturbanceFRESHWATER BIOLOGY, Issue 8 2003Kevin J. Collier Summary 1.,We tested the hypothesis that interactions between disturbance types can influence invertebrate community response and recovery in two streams draining pasture (press-pulse disturbance) and native forest (pulse disturbance) catchments before and after a one-in-28-year flood. We also sampled drift and adult insects to gain insights into the relative importance of these two postdisturbance recolonisation pathways. 2.,Taxa numbers and total density declined markedly at the forested site after the flood, but there was a delayed response at the pasture site, reflecting greater initial resistance to this pulse disturbance among taxa adapted to the underlying press disturbance. 3.,Community composition was less stable at the pasture site where per cent abundance of taxa was highly variable prior to the flood and over the 2-year postflood sampling period. After the flood, the pasture stream fauna was more heavily dominated by vagile taxa, including several chironomid species and hydroptilid caddisflies. 4.,Taxa numbers and densities recovered to preflood levels within 5,7 months at both sites, but a range of taxa-specific responses was observed that took up to 18 months to recover to preflood densities. Community stability at the pasture site had not returned to preflood composition by 2 years postflood. 5.,Changes in drift densities of several common stream invertebrates at the pasture site reflected postflood changes in benthic densities and seasonally low drift in winter. Terrestrial invertebrates dominated drift at the pasture site for 3 months postflood whereas Ephemeroptera were most common at the native forest site. 6.,Flight patterns of selected adult aquatic insects showed a strongly seasonal pattern. Abundance of adults at the pasture site in the second year following the flood increased in line with the recovery of the non-Dipteran benthic fauna. Significant upstream flight occurred for several caddisfly species at the native forest site, and weakly directional or downstream flight was evident for most common Plecoptera and Ephemeroptera. 7.,This study indicates that the magnitude and duration of responses to major pulse disturbances can depend on the presence or absence of an underlying press disturbance. This finding has implications for monitoring, and suggests that a knowledge of disturbance history beyond 2 years may be required to interpret mechanisms contributing to observed land-use impacts. [source] Response of the flora and macroinvertebrate fauna of a chalk stream site to changes in managementFRESHWATER BIOLOGY, Issue 5 2003J. F. Wright SUMMARY 1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50-m section of a chalk stream in Berkshire, England between June 1975,79 and June 1997,2001. 2. The site was part of a trout fishery in 1975,79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997,2001, the site was heavily shaded by trees and riparian vegetation. 3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat. 4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975,79 than in 1997,2001, total family richness for the site in each year did not differ significantly between sampling periods. 5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975,79 and 57 in 1997,2001. This small increase in site family richness may be due to the invading marginal plants. 6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation. 7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources. 8. Whereas macroinvertebrate family richness has been conserved under the recent ,no management' regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout. [source] Alkaloids may not be responsible for endophyte-associated reductions in tall fescue decomposition ratesFUNCTIONAL ECOLOGY, Issue 2 2010Jacob A. Siegrist Summary 1. ,Fungal endophyte , grass symbioses can have dramatic ecological effects, altering individual plant physiology, plant and animal community structure and function, and ecosystem processes such as litter decomposition and nutrient cycling. 2. ,Within the tall fescue (Schedonorus arundinaceus) , fungal endophyte (Neotyphodium coenophialum) symbiosis, fungal produced alkaloids are often invoked as the putative mechanism driving these ecological responses. Yet few measurements of alkaloids exist in the ecological literature. In this study, we quantified alkaloid levels in live, standing dead and decomposing endophyte-infected (E+) and ,free (E,) plant material and simultaneously evaluated the direct and indirect effects of endophyte presence on tall fescue decomposition. 3. ,Loline and ergot alkaloid levels were consistently high in live E+ (common toxic strain of N. coenophialum) tall fescue biomass throughout the sampling period (May,November 2007), whereas, E, live and standing dead material had non-detectable alkaloid concentrations. Standing dead E+ biomass had significantly reduced alkaloid levels (6,19x lower than the levels measured in the corresponding live E+ biomass) that were equivalent to E, live and dead for loline but were still somewhat higher than E, material for ergots. 4. ,In an effort to test the role of alkaloids in directly inhibiting decomposition, as has been suggested by previous studies, we conducted a litter bag experiment using green, alkaloid-laden E+ and alkaloid-free E, tall fescue plant material. We incubated E+ and E, litter bags in both E+ and E, tall fescue stands for 170 days, and measured mass loss, carbon and nitrogen content, and ergot and loline alkaloid concentrations over the incubation period. 5. ,Consistent with previous reports, both direct and indirect effects of endophyte presence on litter decomposition were observed: endophyte presence in the litter and surrounding microenvironment significantly reduced decomposition rates. Surprisingly, despite large differences in alkaloid content between E+ and E, litter from Day 0,Day 21 of the incubation, direct effects of the endophyte on litter decomposition, while significant, were relatively small (differences in mass loss between E+ and E, litter were never >3%). Alkaloids were gone from E+ material by day 56. 6. ,We propose that results from this study indicating alkaloids are largely absent in standing dead material (the typical input to the decomposition process), and that despite being present in our litter bag experiment, failed to produce large differences in mass loss between E+ and E, material questions the supposition that fungal produced alkaloids directly inhibit decomposition. Additional studies exploring the mechanisms behind the direct and indirect effects of endophytes on this ecosystem process are needed. [source] Assessing damaged road verges as a suspended sediment source in the Hampshire Avon catchment, southern United KingdomHYDROLOGICAL PROCESSES, Issue 9 2010A. L. Collins Abstract Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub-catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time-integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub-catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub-catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02,27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub-catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub-catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15,20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley & Sons, Ltd. [source] Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern JapanHYDROLOGICAL PROCESSES, Issue 23 2008Shigeru Mizugaki Abstract To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, 137Cs and 210Pbex were detected by means of gamma-ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The 137Cs and 210Pbex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The 137Cs and 210Pbex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment-mixing model using 137Cs and 210Pbex showed that the contribution of the forest floor varied periodically, ranging from 23,56% in the Hinoki 156 subwatershed and from 18,85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd. [source] Rapid biodiversity assessment of spiders (Araneae) using semi-quantitative sampling: a case study in a Mediterranean forestINSECT CONSERVATION AND DIVERSITY, Issue 2 2008PEDRO CARDOSO Abstract. 1A thorough inventory of a Mediterranean oak forest spider fauna carried out during 2 weeks is presented. It used a semi-quantitative sampling protocol to collect comparable data in a rigorous, rapid and efficient way. Four hundred and eighty samples of one person-hour of work each were collected, mostly inside a delimited 1-ha plot. 2Sampling yielded 10 808 adult spiders representing 204 species. The number of species present at the site was estimated using five different richness estimators (Chao1, Chao2, Jackknife1, Jackknife2 and Michaelis,Menten). The estimates ranged from 232 to 260. The most reliable estimates were provided by the Chao estimators and the least reliable was obtained with the Michaelis,Menten. However, the behavior of the Michaelis,Menten accumulation curves supports the use of this estimator as a stopping or reliability rule. 3Nineteen per cent of the species were represented by a single specimen (singletons) and 12% by just two specimens (doubletons). The presence of locally rare species in this exhaustive inventory is discussed. 4The effects of day, time of day, collector experience and sampling method on the number of adults, number of species and taxonomic composition of the samples are assessed. Sampling method is the single most important factor influencing the results and all methods generate unique species. Time of day is also important, in such way that each combination of method and time of day may be considered as a different method in itself. There are insignificant differences between the collectors in terms of species and number of adult spiders collected. Despite the high collecting effort, the species richness and abundance of spiders remained constant throughout the sampling period. [source] Fault detection of networked control systems with packet based periodic communicationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 8 2009Yongqiang Wang Abstract Fault detection of networked control systems (NCS) with communication constraints is discussed in this paper. A so-called packet-based periodic communication strategy is proposed and two kinds of optimal observer-based residual generators are designed. One residual generator is designed based on the lifted model of NCS, which generates residual signals every communication period. The other works at a faster rate, i.e. it generates residual signals every sampling period and is more suitable for prompt fault detection. Comparison with traditional periodic-communication-sequence-based scheduling strategy reveals superiority of this new communication strategy. Simulation results are also provided to illustrate effectiveness of the proposed method. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of dual-rate systems based on finite impulse response modelsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 7 2004Feng Ding Abstract Two identification algorithms, a least squares and a correlation analysis based, are developed for dual-rate stochastic systems in which the output sampling period is an integer multiple of the input updating period. The basic idea is to use auxiliary FIR models to predict unmeasurable noise-free (true) outputs, and then use these and system inputs to identify parameters of underlying fast single-rate models. The simulation results indicate that the proposed algorithms are effective. Copyright © 2004 John Wiley & Sons, Ltd. [source] Incidence of severe anorexia nervosa in Switzerland: 40 years of developmentINTERNATIONAL JOURNAL OF EATING DISORDERS, Issue 3 2004Gabriella Milos Abstract Objective The current study examined the development of the incidence of severe anorexia nervosa with five sampling periods covering the years 1956,1995 in a geographically defined region of Switzerland. Method Applying the same methodology as in the earlier sampling periods, the medical records of all hospitals of the canton of Zurich were screened manually for first-time hospitalizations of female anorexia nervosa patients during the years 1993,1995. Incidence rates were compared with the previous sampling period (1956,1985). Results The incidence rate of severe anorexia nervosa in the total population and the rate in the population at risk (females 12,25 years old) did not differ significantly from the incidence rates of 1983,1985. Discussion The incidence of severe anorexia nervosa in the canton of Zurich rose significantly during the 1960s and 1970s. Since then, the incidence appears to have reached a plateau. © 2004 by Wiley Periodicals, Inc. Int J Eat Disord 35: 250,258, 2004. An erratum to this article is published in International Journal of Eating Disorders (2004) 36(1) 118,119. [source] Memory effects description by neural networks with delayed feedback connectionsINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 4 2004Petia D. Koprinkova For the purpose of dynamic systems modeling, it was proposed to include feedback connections or delay elements in the classical feed-forward neural network structure so that the present output of the neural network depends on its previous values. These delay elements can be connected to the hidden and/or output neurons of the main neural network. Each delay element gets a value of a state variable at a past time instant and keeps this value during a single sampling period. The groups of delay elements record the values of the state variables for a given time period in the past. Changing the number of the delay elements, which belongs to one group, a shorter or a longer time period in the past can be accounted for. Thus, the connection weights determine the influence of the past process states on the present state in a similar way as it is in the time delay kernel or cause-effect relation membership function (CER-MF) models. Specific feed-forward neural networks with time delay connections are used to solve the problem of neural network chemostat modeling as well as specific kinetic rates modeling. The weights of the feedback connections obtained during model training are discussed as the points of a time delay kernel or as the strength levels in a CER model (the points in the CER-MF). The corresponding changes in these weights with the changing time period in the past are shown. © 2004 Wiley Periodicals, Inc. [source] Necessary and sufficient conditions for solving consensus problems of double-integrator dynamics via sampled controlINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2010Huiyang Liu Abstract In this paper, consensus problems of double-integrator dynamics via sampled control are investigated. The sampled control protocol is induced from continuous-time linear consensus protocol by using periodic sampling technology and zero-order hold circuit. With the obtained sampled control protocol, the continuous-time multi-agent system is equivalently transformed into a linear discrete-time system. Necessary and sufficient conditions are given to guarantee that all the agents asymptotically travel with zero relative positions and common velocities. Furthermore, consensus problem with continuous-time consensus protocol is re-analyzed. A necessary and sufficient condition is also obtained which is consistent with the special case when the sampling period tends to zero. The effectiveness of these algorithms is demonstrated through simulations. Copyright © 2009 John Wiley & Sons, Ltd. [source] Multi-vehicle coordination for double-integrator dynamics under fixed undirected/directed interaction in a sampled-data settingINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2010Yongcan Cao Abstract This paper studies the convergence of two coordination algorithms for double-integrator dynamics under fixed undirected/ directed interaction in a sampled-data setting. The first algorithm guarantees that a team of vehicles achieves coordination on their positions with a zero final velocity while the second algorithm guarantees that a team of vehicles achieves coordination on their positions with a constant final velocity. We show necessary and sufficient conditions on the sampling period, the control gain, and the communication graph such that coordination is achieved using these two algorithms under, respectively, an undirected interaction topology and a directed interaction topology. Tools like matrix theory, bilinear transformation, and Cauchy theorem are used for convergence analysis. Coordination equilibria for both algorithms are also given. Simulation results are presented as a proof of concept. Copyright © 2009 John Wiley & Sons, Ltd. [source] The seasonal abundance of blowflies infesting drying fish in south-west IndiaJOURNAL OF APPLIED ECOLOGY, Issue 2 2001R. Wall Summary 1Blowfly infestation of sun-drying fish is a major economic problem in many developing countries of Asia, Africa and the Pacific. To consider the ecology of infestation, adult and larval blowfly populations were monitored between 27 October 1997 and 27 April 1999 at a fish landing and drying site, approximately 5 km north of Calicut, in Kerala state on the coast of south-west India. 2During the 548-day sampling period, a total of 96 953 adult Diptera was collected from 16 sticky targets, placed inside and outside eight fish-storage sheds. Of these, 91 912 (95%) were Chrysomya megacephala, 3719 (4%) were other Calliphoridae and 1322 (1%) were other species, largely Sarcophagidae. 3The population of C. megacephala showed pronounced seasonal fluctuations in response to climate, particularly relative humidity. Significantly shorter-frequency fluctuations within fish-processing sheds were also evident, the periodicity of which corresponded approximately to C. megacephala generation cycles. Spatial variation in C. megacephala abundance was evident within the site, higher populations occurring closest to the beach and numbers declining with distance inland. 4The pattern of drying fish infestation by C. megacephala broadly followed changes in the density of adult flies and the seasonal change in weather, with peaks during the monsoon and troughs in the dry hot periods. High relative humidity played a significant but secondary role in increasing infestation. 5Quantification of the relationship between larval infestation and percentage fish loss suggests that, given the infestation levels observed, between 10% and 60% post-harvest wet weight losses would be expected in the monsoon period, depending on the species of fish landed. 6The study emphasizes the importance of developing a clear understanding of the basic ecology and spatial and temporal dynamics of an insect pest, prior to the design or implementation of any pest management programme. [source] Influence of non-crop plants on stink bug (Hemiptera: Pentatomidae) and natural enemy abundance in tomatoesJOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2010C. G. Pease Abstract We investigated the effects of weed hosts on stink bug density and damage (Euschistus conspersus Uhler and Thyanta pallidovirens Stal), and a nectar bearing plant on natural enemies of stink bugs in the Sacramento Valley of California. Stink bug density and fruit damage were evaluated in processing tomatoes adjacent to weedy and cultivated borders. The density of E. conspersus was significantly greater in tomatoes adjacent to weedy borders in July but not during August/September. Thyanta pallidovirens was less abundant overall (19%), but was found in significantly greater densities adjacent to cultivated borders in July but not in August/September. Mean percent fruit damage by stink bugs was greater adjacent to the weedy border than the cultivated border, but this difference was not significant. Stink bug egg parasitism and generalist predator density were evaluated in fresh market tomatoes adjacent to a sweet alyssum (Lobularia maritima L.) border and an unplanted control border at three sites. Egg parasitism was significantly greater in the alyssum treatment for the 9,12 September sampling period. Jalysus wickhami VanDuzee (Hemiptera: Berytidae) density was significantly greater in the alyssum treatment in mid-June. No other significant differences in predator populations were detected. Results of these two studies show that habitat manipulations have the potential to reduce densities of E. conspersus in tomato, the first step in developing a farmscape management plan for stink bug control. [source] Parasitism of cotton leafworm Alabama argillacea eggs by Trichogramma pretiosum in commercial cotton fieldsJOURNAL OF APPLIED ENTOMOLOGY, Issue 7 2010C. S. Bastos Abstract Release of natural enemies in commercial fields is challenging and has been inconsistent in the results achieved. This work discusses the augmentative releases of Trichogramma pretiosum to control the cotton leafworm (CLW) Alabama argillacea and also examines the parasitoid,host interaction under grower field conditions. The treatments consisted of fields with and without releases of T. pretiosum set up in Primavera do Leste and Campo Verde Counties, MT, Brazil, during three different seasons (2003 and 2004 dry and 2004 regular summer seasons). Trichogramma wasps were weekly released in the treated fields throughout the entire sampling period (14,15 week period) at a rate of 100 000 wasps per hectare. One-way repeated measures analysis of variance was performed for the number of parasitized eggs, followed by a meta-analysis procedure to determine the contribution of T. pretiosum release on overall parasitism. In addition, regression analysis was conducted with each season's data sets to study the relationship of the host density and parasitism response by T. pretiosum. The overall results of Trichogramma augmentative releases did not result in significant increase of CLW egg parasitism beyond the natural parasitism in the areas studied. However, based on Cohen's d effect sizes from the meta-analysis, the parasitism rate was greater in fields under T. pretiosum releases during four out of 15 weeks surveyed. The parasitism of CLW eggs by T. pretiosum exhibited host density-dependence only in one out of three seasons surveyed. These findings are encouraging as they are evidence that T. pretiosum is able to maintain a considerable level of parasitism under commercial field conditions, highlighting their potential value in large-scale commercial areas of cotton as previously found at the small and diverse farming scale. Future studies should address the potential of early-season, low density releases of the parasitoid. [source] Do larval fishes exhibit diel drift patterns in a large, turbid river?JOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2010K. S. Reeves Summary Previous research suggested larval fishes do not exhibit a diel drift cycle in turbid rivers (transparency <30 cm). We evaluated this hypothesis in the turbid, lower Missouri River, Missouri. We also reviewed diel patterns of larval drift over a range of transparencies in rivers worldwide. Larval fishes were collected from the Missouri River primary channel every 4 h per 24-h period during spring-summer 2002. Water transparency was measured during this period and summarized for previous years. Diel drift patterns were analyzed at the assemblage level and lower taxonomic levels for abundant groups. Day and night larval fish catch-per-unit-effort (CPUE) was compared for the entire May through August sampling period and spring (May , June) and summer (July , August) seasons separately. There were no significant differences between day and night CPUE at the assemblage level for the entire sampling period or for the spring and summer seasons. However, Hiodon alosoides, Carpiodes/Ictiobus spp. and Macrhybopsis spp. exhibited a diel cycle of abundance within the drift. This pattern was evident although mean Secchi depth (transparency) ranged from 4 to 25 cm during the study and was <30 cm from May through August over the previous nine years. Larval diel drift studies from 48 rivers excluding the Missouri River indicated the primary drift period for larval fishes was at night in 38 rivers and during the day for five, with the remaining rivers showing no pattern. Water transparency was reported for 10 rivers with six being <30 cm or ,low'. Two of these six turbid rivers exhibited significant diel drift patterns. The effect of water transparency on diel drift of larval fishes appears taxa-specific and patterns of abundant taxa could mask patterns of rare taxa when analyzed only at the assemblage level. [source] Predicting and managing the effects of hypersalinity on the fish community in solar salt fields in north-western AustraliaJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2 2006B. W. Molony Summary Five concentrator ponds (CPs) of a solar salt field in Port Hedland, Western Australia were sampled by seine and gill nets over a 12-month period in order to describe the fish community and examine relationships between diversity, abundance and catch per unit effort (CPUE) with salinity. Salinity varied between 40.2 and 113.7, during the sampling period. Forty-one species of fishes were recorded from the CPs, with fewer species recorded from CPs of higher salinity. A significant inverse relationship was identified between salinity and the number of species (diversity) captured in gill nets, indicating that one species is lost with every 16, increase in salinity. A significant relationship between salinity and CPUE was also identified with gill-net samples, indicating a reduction of 1 kg h,1 with every increase in salinity of 5.5,. As CPs are connected by one-way flaps, fish movements are only possible into CPs of higher salinity. Thus, reductions in diversity, abundance and CPUE suggested fish mortalities, likely as a result of maximum or rapidly changing salinities exceeding the tolerance ability of individual species. As fish kills are not infrequent events in solar salt fields and result in economic losses due to loss of production and clean-up costs, the results may allow managers to identify high risk species and times of year of fish kills by using salinity measurements. Commercial, indigenous and/or recreational fishing opportunities are viable options for reducing fish biomasses within the CPs and are discussed. Although absolute salinity values were higher than those recorded from tropical Australian estuaries, salinity deviations within each CP are similar to other estuaries and the effect on the ichthyo-community is likely to be similar. [source] Genotyping of Campylobacter spp. from retail meats by pulsed-field gel electrophoresis and ribotypingJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2006B. Ge Abstract Aims:, To determine the genetic relatedness of Campylobacter spp. from retail meat products, and compare the discriminatory power of pulsed-field gel electrophoresis (PFGE) and automatic ribotyping. Methods and Results:, A total of 378 Campylobacter isolates recovered from 159 raw meats (130 chicken, 25 turkey, three pork and one beef) sampled from 50 retail grocery stores of four supermarket chains in the Maryland suburban area from August 1999 to July 2000 were analysed by PFGE with SmaI, 120 isolates of which were also characterized by ribotyping with PstI using RiboPrinter® system. A total of 148 unique PFGE patterns were identified, 91 of which were present in multiple Campylobacter isolates and 24 in multiple meat samples. Nineteen Campylobacter clones with identical PFGE patterns recurred frequently (up to nine times) throughout the sampling period. Comparing ribotyping with PFGE, we identified 44 PFGE patterns and 22 RiboGroups among the 120 isolates tested. Multiple PFGE patterns within one RiboGroup were commonly observed, as well as multiple RiboGroups within one PFGE pattern. Conclusions:, Although Campylobacter present in retail meats were genetically diverse, certain clones persisted in poultry meats. PFGE had a greater discriminatory power than ribotyping, and the two methods were complementary in genotyping Campylobacter. Significance and Impact of the Study:, Genomic DNA fingerprinting of Campylobacter confirmed diverse and recurrent Campylobacter clones in the retail meats, which provides additional data for a better understanding of the epidemiological aspect of Campylobacter infection. [source] Heard but not seen: an acoustic survey of the African forest elephant population at Kakum Conservation Area, GhanaAFRICAN JOURNAL OF ECOLOGY, Issue 1 2010Mya E. Thompson Abstract This study, designed to survey forest elephants (Loxodonta africana cyclotis) at Kakum Conservation Area, Ghana, is the first to apply acoustic methods to elephant abundance estimation and to compare results with independent survey estimates. Nine acoustic sensors gathered sound continuously for 38 days. Low-frequency calling rates have been established as useful elephant abundance indices at a Namibian watering hole and a central African forest clearing. In this study, we estimated elephant population size by applying an abundance index model and detection function developed in central Africa to data from simultaneous sampling periods on Kakum sensors. The sensor array recorded an average of 1.81 calls per 20-min sampling period from an effective detection area averaging 10.27 km2. The resulting estimate of 294 elephants (95% CI: 259,329) falls within confidence bounds of recent dung-based surveys. An extended acoustic model, estimating the frequency with which elephants are silent when present, yields an estimate of 350 elephants (95% CI: 315,384). Acoustic survey confidence intervals are at least half as wide as those from dung-based surveys. This study demonstrates that acoustic surveying is a valuable tool for estimating elephant abundance, as well as for detecting other vocal species and anthropogenic noises that may be associated with poaching. Résumé Cette étude, conçue pour étudier les éléphants de forêt (Loxodonta africana cyclotis) de l'Aire de conservation de Kakum, au Ghana, est la première qui applique des méthodes acoustiques pour l'estimation de l'abondance des éléphants et qui compare les résultats avec des estimations indépendantes. Pendant 38 jours, neuf senseurs acoustiques ont récolté les sons en continu. Le rythme des appels à basse fréquence est un indice utile de l'abondance des éléphants que l'on a pu établir à un point d'eau en Namibie et dans une clairière d'une forêt d'Afrique centrale. Ici, nous estimons la taille d'une population d'éléphants en appliquant un modèle d'indice d'abondance et une fonction de détection mis au point en Afrique centrale à des données provenant des senseurs de Kakum pour des périodes d'échantillonnage simultanées. La batterie de senseurs a enregistré une moyenne de 1.81 appel par 20 min, pour une superficie de détection réelle de 10.27 km² en moyenne. L'estimation qui en résulte, qui est de 294 éléphants (95% IC 259,329), tombe dans les limites de confiance de récentes études basées sur les crottes. Un modèle acoustique étendu, qui estime aussi la fréquence à laquelle les éléphants sont silencieux pendant leur présence, donne une estimation de 350 éléphants (95% IC 315,384). Les intervalles de confiance d'une étude acoustique sont au moins la moitié de ceux des études par les crottes. Cette étude montre que l'étude acoustique est un outil intéressant pour estimer l'abondance des éléphants et aussi pour détecter d'autres espèces bruyantes et les bruits d'origine anthropique qui pourraient être associés au braconnage. [source] Temporal variability in marine feeding of sympatric Arctic charr and sea troutJOURNAL OF FISH BIOLOGY, Issue 3 2007A. H. Rikardsen The marine feeding pattern of anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus was studied during June to August in 1992,1993 and 2000,2004 in a fjord in northern Norway. In general sea trout fed proportionally more on fishes than on crustaceans and insects (81, 1 and 18% by mass, respectively) by comparison with Arctic charr (52, 25 and 22% by mass, respectively). Herring Clupea harengus dominated the total fish diet of both species, but the Arctic charr also fed significantly on gadoids and sandlance Ammodytes spp. While sea trout became virtually all piscivorous at fork lengths (LF) ,250 mm, the Arctic charr was ,400 mm LF before shifting totally to a fish diet. Despite annual variation in diet and forage ratios, there was a clear shift in diet from 1992,1993 to 2000,2004. Sandlance and different crustaceans constituted most of the diet during the initial period with a shift towards gadoids and especially herring during the latter period. This shift seemed to be associated with a high abundance of herring larvae during the latter sampling period, indicating a preferential selection on herring when present, particularly by sea trout. Furthermore, an index indicated dietary overlap in years with intensive feeding on herring of both species, and usually differences in the trophic ecology during years feeding mostly on other prey species. In combination, it was hypothesized that the two species reflect the type of marine prey present within a fjord system over time, and therefore provide an index of variation in the production and biological diversity of their potential prey within fjords. [source] Temporal changes in Sander vitreus egg thiamine levelsJOURNAL OF FISH BIOLOGY, Issue 4 2005M. E. Barnes Thiamine pyrophosphate was the predominant form of thiamine present initially in walleye Sander vitreus eggs from two spawning locations in Lake Oahe, South Dakota, U.S.A. Total thiamine content in the eggs at fertilization was 5·18 and 7·97 nmol g,1 for eggs from the Moreau and Grand River spawning sites respectively, and egg thiamine content in all its forms dropped dramatically at the next sampling period of 48 temperature units (TU). Thiamine values did not significantly drop after the 48 TU period, but mean total thiamine composition was < 0·9 nmol g,1 at the last sampling date (156 TU) just prior to hatching. [source] Surveillance of health status on eight marine rainbow trout, Oncorhynchus mykiss (Walbaum), farms in Denmark in 2006JOURNAL OF FISH DISEASES, Issue 9 2008K Pedersen Abstract The health status of eight marine rainbow trout farms was followed from mid-June to mid-September 2006 by sampling both dead and healthy fish approximately every 2 weeks for bacteriological and virological investigation. No fish pathogenic viruses were detected, but all farms experienced disease and mortality as a result of various bacterial infections. Yersinia ruckeri was found on four and Renibacterium salmoninarum on five of the farms, but only during the first part of the surveillance period. This indicates that the fish carried the infection from fresh water, and cleared the infection in salt water. Aeromonas salmonicida subsp. salmonicida caused mortality on five farms, but persisted throughout the sampling period. Although A. salmonicida was probably carried from fresh water, the fish were not able to clear the infection in the sea. Vibrio anguillarum caused mortality on six of the farms throughout the sampling period, O1 being the dominant serovar, and Photobacterium damselae subsp. damselae was found on seven farms as a cause of disease. During the period of highest water temperatures Vibrio parahaemolyticus and Vibrio vulnificus were detected in dead fish in five and two farms, respectively, although their significance as causative pathogens is questionable. Vibrio vulnificus has not previously been found in rainbow trout in Denmark. Both mortality and number of antimicrobial treatments during the period were considerably higher in unvaccinated compared with vaccinated fish. Resistance to commonly used antimicrobials was low or absent. [source] Sporadic neoplasms of farmed chinook salmon, Oncorhynchus tshawytscha (Walbaum), from New ZealandJOURNAL OF FISH DISEASES, Issue 7 2003J S Lumsden Abstract Eight separate neoplasms with five distinct morphologies are described in the present report. The spontaneous neoplasms were identified in farmed chinook salmon, Oncorhynchus tshawytscha (Walbaum), during processing. The masses were examined histologically and were classified as teratoma, rhabdosarcoma, biliary and renal cystadenomas, renal carcinoma and three leiomyomas. This represents one neoplasm detected for every 125 000 fish processed during the sampling period. [source] Effect of Seasonality on Distribution of Macroalgae in a Stream System (Xin'an Spring) in Shanxi Province, North ChinaJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 8 2006Bian-Fang Hu Abstract A survey of the seasonal distribution of macroalgae in a stream system in Shanxi Province, north China, was undertaken from July 2004 to April 2005. The relative abundance and percentage cover of macroalgae, and several environmental factors were monitored along a 20-m stretch at each of four sites, at intervals of approximately three months (one sampling per season). Several stream conditions were relatively constant over the sampling period (pH, maximum width and maximum depth), whereas others exhibited a distinct seasonal pattern (water temperature and specific conductance), and some fluctuated with no discernable seasonal pattern (current velocity and dissolved oxygen). Forty-two species of macroalgae were found, with a predominance of Chlorophyta (26 species, 61.9%). Rhodophyta and Charophyta represented the smallest proportion (1 species each, 2.38%). Six macroalgae species were the most widespread, occurring in all four sampling sites. Twelve species were found at only one site each. In terms of seasonality, eight species occurred throughout the year, whereas 16 species were found in only one season each. The macroalgal community at Xin'an Spring was species rich relative to other streams. Species richness per sampling site was negatively correlated with pH. Principal component analysis revealed that no single variable had much influence on the macroalgal seasonal dynamics. We calculated Sorensen similarity indices to compare our study with other continent-wide surveys of stream macroalgae, but the similarity indices were all very low. This study also shows that macroalgae in different locations have significant reproductive isolation. (Managing editor: Ya-Qin Han) [source] Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterialsJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 10 2005David S. Jones This study examined the effects of concentration and type of crosslinker (tetraethyleneglycol diacrylate, TEGDA; diethyleneglycol dimethacrylate, DEGDMA; and polyethyleneglycol dimethacrylate, PEGDMA) on the mechanical and drug diffusional properties of hydrogels that had been selected as candidate coatings for bioactive medical devices. Hydrogels (dimethylaminoethylmethacrylate-covinylpyrrolidone; 1:1) were prepared by free radical polymerization and characterized using tensile analysis, dynamic contact angle analysis and analysis of swelling at pH 6.0. The release of fusidic acid and chlorhexidine was evaluated using buffered medium at pH 6.0 and, in addition, using dissolution medium that had been buffered to pH 9 in the presence and absence of elevated concentrations of calcium, representative of urinary encrustation. Crosslinker concentration, but not type, affected the advancing and receding contact angles. Conversely, both crosslinker type and concentration affected the mechanical and swelling properties of the hydrogels. Maximum swelling and elongation at break were associated with the PEGDMA-crosslinked hydrogels whereas TEGDA-crosslinked hydrogels exhibited the maximum ultimate tensile strength and Young's modulus. Drug release from all systems occurred by diffusion. The mass of chlorhexidine and fusidic acid released was dependent on crosslinker type and concentration, with hydrogels crosslinked with PEGDMA offering the greatest mass of drug released at each sampling period. The mass of fusidic acid but not chlorhexidine released at pH 9.0 in a calcium augmented medium was lower than that released in the same medium devoid of elevated calcium, due to the formation of the poorly soluble calcium salt. In conclusion, this study has uniquely examined the effects of crosslinker type and concentration on physicochemical and drug release properties essential to the clinical and non-clinical performance of bioactive hydrogels for medical device application. [source] | |||||||||||||||||||||||||||||||||||||||||||