bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion of fish from a single release point
Authors: Sparrevohn Claus R , Nielsen Anders , Støttrup Josianne G
Published: October 2002

In a field experiment, 3529 turbot (Psetta maxima) were released in order to estimate and describe the movements of hatchery-reared fish by applying diffusion theory. After liberation, the development of the population density was estimated during the following 9 days, and from that, the rate of diffusion and the advection were determined. Two approaches were followed to describe the data: a normal distribution approximation (NDA) model and a partial differential equation (PDE) model. In the latter, it was possible to include the effect of sampling. The two models gave similar results, indicating that the sampling of fish during the experiment did not have any detectable effect on the population density. The activity of the released turbot resulted in an individual daily displacement of 151 m·day1, except for the first 2 days at liberty, where the displacement was estimated to be considerably lower. Advection was significant and was related to the displacement of the water body. Further, it was possible to estimate the postrelease mortality as 14%·day1and the catchability of the turbot when caught with a young fish trawl as 28%.
Evolutionary individual-based model for the recruitment of anchovy (Engraulis capensis) in the southern Benguela
Authors: Mullon Christian , Cury Philippe , Penven Pierrick
Published: October 2002

Evolutionary simulations are developed to explore environmental constraints that select observed spatial and temporal spawning patterns for anchovy (Engraulis capensis) in the southern Benguela. They couple a realistic three-dimensional hydrodynamic model with an individual-based model in which an evolutionary-based reproductive strategy for adult fish and a passive transport for early life stages are implemented. The evolutionary success of spawning is quantified when patterns at the population level emerge after many generations from constraints at the individual level through a selective process. As a result, several self-sustaining populations are identified considering different sets of selective constraints. Simulated spawning patterns better match the observed mean spawning pattern when two selective environmental constraints are associated: a threshold temperature of 14°C, above which the development of early life stages is ensured, and the avoidance of offshore currents that constitute a loss of spawning products. Simulated recruitment patterns are more realistic when considering the constraint of reaching the nursery area. This modeling experience can help to identify, temporally and spatially, environmental factors important for fish recruitment and to establish a hierarchy of these factors. The probable coexistence in nature of several self-sustaining populations of pelagic fishes is shown to be important for recruitment studies.
Resistance to three pathogens in the endangered winter-run chinook salmon (Oncorhynchus tshawytscha): effects of inbreeding and major histocompatibility complex genotypes
Authors: Arkush Kristen D , Giese Alan R , Mendonca Holly L , McBride Anne M , Marty Gary D , Hedrick Philip W
Published: October 2002

We have carried out the first major infectivity trial to examine differential genetic resistance in fish for pathogens. We used captive-bred, endangered winter-run chinook salmon (Oncorhynchus tshawytscha) to determine resistance to three pathogens: the bacterium, Listonella (Vibrio) anguillarum, infectious hematopoietic necrosis virus (IHNV), and Myxobolus cerebralis, the parasite that causes whirling disease. We compared resistance to these three pathogens between inbred and outbred salmon and between siblings that were heterozygous or homozygous for a class II gene in the major histocompatibility complex (MHC). In two of five different comparisons, we found significant genetic effects on disease resistance. First, MHC heterozygotes had a higher survival than MHC homozygotes when exposed to IHNV and the selection disadvantage of homozygotes was estimated to be 8.5%. Second, outbred fish had a higher resistance (or lower infection severity) than inbred fish when exposed to M. cerebralis. Using a quantitative genetics approach, it appears that there are slightly more than three gene equivalents segregating that would result in no resistance to M. cerebralis when homozygous. Overall, our investigation suggests that pathogen susceptibility in the winter-run chinook salmon will increase if further genetic variation is lost in this endangered species.
Long-term response of periphyton and macrophytes to reduced municipal nutrient loading to the Bow River (Alberta, Canada)
Authors: Sosiak Al
Published: October 2002

The biomass of periphyton and aquatic macrophytes (Potamogeton vaginatus and Potamogeton pectinatus) in the Bow River was sampled over 16 years to assess the response of these plants to improved phosphorus (19821983) and nitrogen removal (19871990) at Calgary's two municipal wastewater treatment plants. These improvements in treatment reduced total phosphorus loading to the Bow River by 80%, total ammonia loading by 53%, and nitrite + nitrate loading by 50%. No change in periphytic biomass was detected after enhanced phosphorus removal where total dissolved phosphorus (TDP) in river water remained relatively high (1033 μg·L1). However, periphytic biomass declined at sites further downstream with TDP < 10 μg·L1. Regression analysis predicted that nuisance periphyton biomass (>150 mg·m2) occurred at TDP > 6.4 μg·L1 (95% confidence interval: 1.97.6 μg·L1). Macrophyte biomass was inversely correlated with discharge and was lower during high-discharge years. Biomass also declined following enhanced nutrient removal, with the greatest decrease following reduced nitrogen discharge. These results provide the first evidence for a response of periphyton and aquatic macrophytes to enhanced nutrient removal from municipal wastewater.
Species identification in deep water using multiple acoustic frequencies
Authors: Kloser R J , Ryan T , Sakov P , Williams A , Koslow J A
Published: October 2002

Multifrequency 12, 38, and 120 kHz acoustics were used to identify the dominant fish groups around a deepwater (>600 m) seamount (a known spawning site for orange roughy, Hoplostethus atlanticus) by amplitude mixing of the frequencies. This method showed three distinct acoustic groupings that corresponded to three groups of fishes based on size and swimbladder type: myctophids of total length less than 10 cm, morids and macrourids with lengths >30 cm, and orange roughy with a mean standard length of 36 cm. These three groups were the dominant groups caught in the demersal and pelagic trawls in the study area. A simple model of swimbladder resonance at depth of large and small gas-filled bladder fish groups is in agreement with our experimental observations. Traditionally, demersal and pelagic trawling is used to identify fish species in acoustic records. However, orange roughy are rarely caught in mid-water owing to net avoidance. Using three frequencies, these groups could be distinguished directly over their entire vertical extent from the acoustic records. This reduces a major source of positive bias uncertainty (factor range of 2.06.4) in the orange roughy biomass estimates.
Effects of food and cover on the growth, survival, and movement of cutthroat trout (Oncorhynchus clarki) in coastal streams
Authors: Boss Shelly M , Richardson John S
Published: October 2002

To examine the extent to which stream-resident coastal cutthroat trout (Oncorhynchus clarki) are limited by food and cover, we manipulated these two factors in a 2 × 2 design using enclosures containing 1-year-old trout in two streams. During summer, fish receiving food additions experienced an average growth rate of 1.73% body mass·day1 compared with a rate of 0.022 for unfed fish (ambient food supply only), indicating marked food limitation. The addition of cover decreased mortality by approximately 50% in one stream, but survival was high both with and without cover in the other. There was no interaction of food and cover on growth or survival. Emigration rates were low and were not strongly affected by either factor. We also used markrecapture modeling to examine whether the 48% greater mass of fed fish at the end of the experiment improved survival over winter. Fed fish were still 46% larger than unfed fish by the next spring, but overwinter survival was not explained by body size. Our results show that, during summer, food availability can limit trout growth, and cover, by mediating predation, can limit survival.
Year-class detection reveals climatic modulation of settlement strength in the European lobster, Homarus gammarus
Authors: Sheehy M R.J , Bannister R C.A
Published: October 2002

Understanding the nature of recruitment relationships in the European lobster, Homarus gammarus, has been an intractable problem because of difficulties associated with quantification of its scarce planktonic larvae and early benthic phase. We attempt to address this problem by analyzing the age composition of a population off the northeast coast of England. Age-dependent in situ deposits of neurolipofuscin in the eyestalk are used as an age index. An approach is presented that accounts and (or) corrects for the two most important potential sources of error in age determinations by this technique, namely environmental temperature variation and unexplained individual variation. This yields, for the first time in very long-lived clawed lobsters, reproducible catch age structures with year-class resolution. The method should be generally applicable to crustaceans. Cross-correlation analysis shows that larval settlement strength in the European lobster is associated with local sea temperatures and onshore winds in a manner similar to that reported for other lobsters. These findings have important implications for stock assessment, particularly the use of traditional models dependent on size and steady state, yield forecasting, the effects of global climate change, arguments about spawner protection or restocking, and the spawnerrecruit relationship.
Modeling ships' ballast water as invasion threats to the Great Lakes
Authors: MacIsaac Hugh J , Robbins Thomas C , Lewis Mark A
Published: October 2002

The spread of nonindigenous species (NIS) in aquatic ecosystems provides an opportunity to develop new perspectives on the invasion process. In this paper we review existing invasion models, most of which were developed to describe invasions of terrestrial habitats, and propose an alternative that explores long-distance invasions mediated by discharge of contaminated ballast water by ships inbound to the Great Lakes. Based on current knowledge of shipping traffic to the Great Lakes, our model predicts that mid-ocean exchange of ballast water lowers propagule delivery by approximately three to four orders of magnitude relative to unexchanged ballast water. Propagule pressure of individual ships that enter the Great Lakes loaded with cargo and that declare "no ballast on board" (NOBOB) is typically one to two orders of magnitude higher than that of vessels that exchange ballast. Because NOBOB vessels dominate (~90%) inbound traffic into the Great Lakes, these vessels collectively appear to pose the greatest risk of new introductions, even though their individual risks are low.
Geographical patterns in range extension of Ponto-Caspian macroinvertebrate species in Europe
Authors: Bij de Vaate A , Jazdzewski K , Ketelaars H A.M , Gollasch S , Van der Velde G
Published: October 2002

Range extensions of aquatic Ponto-Caspian macroinvertebrate species in Europe have mainly been facilitated by the interconnection of river basins through man-made canals and intentional introductions. Three inland migration corridors can be distinguished: (i) a northern corridor: Volga [Formula: see text] Lake Beloye [Formula: see text] Lake Onega [Formula: see text] Lake Ladoga [Formula: see text] Neva [Formula: see text] Baltic Sea, (ii) a central corridor connecting the rivers Dnieper [Formula: see text] Vistula [Formula: see text] Oder [Formula: see text] Elbe [Formula: see text] Rhine, and (iii) a southern corridor connecting the Danube and Rhine rivers. Important trade harbours in Europe were connected via these corridors allowing further range extensions of macroinvertebrate species attached to a vessel's hull or in ballast water. The central corridor was the main migration route before 1992, after which the southern corridor became the most important migration route for the range expansions to the west because of the reopening of the Main-Danube Canal, connecting the Rhine and Danube basins. Especially the water level maintenance in the upper part of the canal, with water supply from the Danube basin, facilitated migration of mobile animals (e.g., crustaceans) from the Danube basin towards the Rhine basin; however, contribution of other transport mechanisms (e.g., shipping) is expected in the near future.
Modified rational method for sizing infiltration structures
Authors: Akan A Osman
Published: October 2002

A simple method is presented to size infiltration structures like infiltration basins and trenches to control storm water runoff. The runoff hydrograph is assumed to be trapezoidal in shape with a peak runoff rate calculated using the rational formula. Given the watershed time of concentration and the allowable runoff rate, the method determines the required size of the infiltration structure. A practical application section is included to demonstrate the use of the method.Key words: rational method, infiltration basin, infiltration trench, capture volume, storage time.
Evaluation of flexural fracture toughness for quasi-brittle structural materials using a simple test method
Authors: Taha M.M Reda , Xiao X , Yi J , Shrive N G
Published: October 2002

As new structural concepts such as partial prestressing and steel-free bridge decks are more widely accepted and used, there is an increasing need for a reliable and reproducible fracture performance criterion that can describe resistance to crack growth. The required criterion should also be easy to determine experimentally so that it can be incorporated in structural specifications. The nonlinear behaviour of concrete and masonry materials suggested that quasi-brittle fracture mechanics approaches may be the most suitable for determining their fracture performance. The effective elastic crack model originally developed by Karihaloo and Nallathambi (1989) was modified to evaluate the critical crack depth under pure flexural stresses. A computer program was developed to calculate this depth iteratively from the experimental results. An experimental programme examining the fracture performance of four different structural materials (high performance concrete, mortar, fibre reinforced concrete, and masonry units) was carried out to examine the applicability of the model. As no post-peak data are required for the analysis, the model allows the use of a simple test setup to evaluate the fracture performance of quasi-brittle materials experimentally.Key words: fracture toughness, linear elastic fracture mechanics (LEFM), elastoplastic fracture mechanics (EPFM), quasi-brittle fracture mechanics, effective elastic crack, high performance concrete, masonry, fibre reinforced concrete.
Rehabilitation of reinforced concrete slabcolumn connections
Authors: El-Salakawy Ehab F , Polak Maria Anna , Soudki Khaled A
Published: October 2002

The paper presents work on punching shear rehabilitation and strengthening of existing slabcolumn connections. Four full-scale specimens representing slabcolumn edge connections were built and tested to failure. Three slabs were then repaired and strengthened and tested again. In the originally tested slabs, which were chosen for repair, one slab had an opening in front of the column and contained shear reinforcement, one slab had an opening and no shear reinforcement, and one had no opening and no reinforcement. The dimensions of the slabs were 1540 × 1020 × 120 mm with square columns (250 × 250 mm). The openings in the specimens were square (150 × 150 mm) with the sides parallel to the sides of the column. The slabs were made using normal weight concrete (28-day average compressive strength of 32 MPa) and reinforced with a reinforcement ratio of 0.75%. The slabs were repaired by replacing old-damaged concrete with new concrete of the same properties. Strengthening was carried out using shear studs for the two slabs, which originally did not have shear reinforcement. The rehabilitation increased the punching shear strength (by 2641%) and the ductility of the connections. All repaired specimens failed in flexure.Key words: concrete slabs, punching shear, rehabilitation, edge connections, openings, studs, repair.
Nonresonant effects in one- and two-photon transitions
Authors: Jentschura U D , Mohr P J
Published: October 2002

We investigate nonresonant contributions to resonant Rayleigh-scattering cross sections of atoms. The problematic nonresonant contributions set a limit to the accuracy to which atomic spectra determine energy levels. We discuss the off-resonance effects in one-photon transitions. We also show that off-resonance contributions for the 1S2S two-photon transition in atomic hydrogen are negligible at current and projected levels of experimental accuracy. The possibility of a differential measurement for the detection of off-resonance effects in one-photon transitions in atomic hydrogen is discussed.

PACS Nos.: 31.15-p, 12.20Ds
Diffraction by a set of three parallel impedance half-planes with the one amidst located in the opposite direction
Authors: Çinar G , Büyükaksoy A
Published: October 2002

The problem of diffraction of plane waves by a set of three parallel half-planes with different surface impedances on upper and lower faces where the one in the middle is placed in the opposite direction, is solved by the mode-matching method where available, and by Fourier-transform technique elsewhere. The solution includes two independent WienerHopf equations each involving an infinite number of expansion coefficients that satisfy an infinite system of linear algebraic equations.

PACS No.: 41.20J
Localization of a bound particle outside the potential well
Authors: Holub R F , Smrz P K
Published: October 2002

We describe a simple effect predicted by standard quantum mechanics concerning a particle bound in a potential well brought to the zero-energy state by deformation of the well. When the effect takes place within a crack with impermeable walls the probability of localization of the particle reaches its maximum near the end of the crack. The wave function describing the bound particle may thus decohere far from the potential well. There are numerous instances of experimental data, gathered mostly by geochemists and other scientists over the last several decades, that are anomalous and defy all attempts to explain them by means of classical chemistry and physics. The common attribute of these data is a strange transport of particles over large distances that may be caused by the quantum effect described in the first part of the paper. The motivation for writing this paper is our hope to stimulate interest and critical testing of such an hypothesis.

PACS Nos.: 03.65, 82.90, 91.90
The treatment of high strength wastewater containing high concentrations of ammonium in a staged anaerobic and aerobic membrane bioreactor
Authors: Zhang Daijun , Verstraete Willy
Published: October 2002

In this paper, a staged anaerobic and aerobic membrane bioreactor was constructed and used to study the treatment of high strength wastewater containing high concentrations of ammonium. The membrane module was submerged in the aerobic zone (upper part) of the bioreactor and was operated under an alternating suction mode and air backwash mode. Air backwash and aeration around the membrane module served as the cleaning mechanism for the membrane; this resulted in the steady operation of the reactor at the flux of 514 L m2 h1 for 120200 h without any additional cleaning. The efficiencies of the chemical oxygen demand (COD) removal were >99% for up to 10.08 g COD L1 d1 of the volumetric loading rate. Between 60 and 80% of COD was anaerobically biodegraded in the anaerobic zone (lower part) of the reactor and converted to methane that could serve as a carbon source for the denitrification in the upper part of the reactor. The intermittent aeration resulted in simultaneous nitrification and denitrification in the aerobic zone of the reactor. The capacity of the ammonium removal reached 0.5 g NH4+-N L1 d1. Between 84 and 94% of the total oxidized nitrogen converted from the oxidization of ammonium was denitrified. Key words: air backwash membrane bioreactor (MBR), high strength wastewater, anaerobic and aerobic treatment, ammonium removal, methanotrophic denitrification.
On the high stress compression of bentonites
Authors: Marcial Duilio , Delage Pierre , Cui Yu Jun
Published: October 2002

High stress consolidation tests (up to 30 MPa) were carried out on slurries made up of three bentonites considered as possible constituents for engineered clay barriers used for nuclear waste disposal at great depth (Na Kunigel, Na-Ca MX80 Wyoming clay, and Ca Fourges clay). Water retention curves (WRCs) were determined for a wide range of suctions (up to 305 MPa). A bilinear shape for the compression curves and the WRCs was observed in the three clays, with significant changes occurring in the 0.41 MPa suctionstress range. The permeability and the coefficient of consolidation were also determined during the compression tests. In the WRCs and compression curves, the two clays containing Na+ exhibited a similar behaviour, which was different from that of the Ca2+ clay. The coefficient of consolidation for the three clays was decreasing in the 0.41 MPa stress range and increasing at higher stresses. Data were interpreted in the light of existing experimental observations on the microstructural changes of similar swelling clays carried out by various authors, which obtained compatible and coherent results. The diffuse double theory, often used in the interpretation of the volume change behaviour of swelling clays, was also considered. Under higher stresses (> 2 MPa), the compressive behaviour appeared to be linked to the expulsion water molecules that form the hydration shells around exchangeable cations inside the domains formed of staked clay plates. The permeability properties of the Ca2+ and Na+ clays were linked to the microstructure features and to the WRCs, whereas the changes in the coefficients of consolidation during compression were linked to the changes in soil stiffness.Key words: consolidation, swelling clay, permeability, exchangeable cations, diffuse double layer, adsorbed water.
A possible elasticplastic framework for unsaturated soils with high-plasticity
Authors: Tang Gary X , Graham James
Published: October 2002

The paper proposes a new elasticplastic framework for unsaturated, high-plasticity, clayey soils and sandclay mixtures. The framework considers possible coupling of stress- and suction-induced hardening, leading to a yield surface that is closed or "capped" as suctions increase. This produces a stress state boundary surface in three-dimensional pqs stress space (where p is the net mean stress, q is the deviator stress, and s is the matric suction) which differs from that of other conceptual models of its kind. Yielding, a hardening law, and failure criteria for saturated soils are incorporated into the stress state boundary surface. Two parameters, equivalent pressure pe and stress ratio ηs, are introduced to form the basis of the proposed elasticplastic framework for highly plastic soils with high suctions. This provides an alternative for the stress variables net mean stress and matric suction that are commonly used in modeling unsaturated soils with lower plasticity and lower suctions. This framework has allowed results of experiments on an unsaturated sandbentonite mixture to be successfully described using elastoplasticity. Yield and failure envelopes associated with the proposed state boundary surface in pqs space can be normalized using pe and ηs in such a way that they agree with a comparable envelope for saturated specimens. Key words: unsaturated, elasticplastic, triaxial, matric suction, state boundary surface, sand-bentonite.
Post-failure mobility of saturated sands in undrained load-controlled ring shear tests
Authors: Wang Gonghui , Sassa Kyoji
Published: October 2002

The undrained shear behavior of soils with progress of shear displacement is essential to the understanding of liquefied slope failures with long travel distance. In this paper, using a newly developed ring shear apparatus, a series of ring-shear tests were conducted on a silty sand to examine the undrained behavior of sand subjected to long shear displacement. Based on the test results, the undrained shear behavior of sands with a wide range of densities is discussed. A very low effective stress corresponding to liquefaction was observed at the steady state in all of the tests on loose, medium, as well as dense sand. The effects of stress state and shear history on the undrained shear behavior were examined by performing tests on a sample with different initial stress states and shearing the same specimen repeatedly (three times) at each initial stress state. The tests at different initial stress states proved that the initial stress state has an influence on static liquefaction resistance but has no effect on the steady-state shear strength. Repeated shear tests on the same specimen showed that with increasing shear times, both the peak shear strength and the steady-state shear strength for each specimen became greater. Detailed examination of the shear deformation revealed that the liquefaction phenomena in ring shear tests are localized in the shear zone, irrespective of the initial state of the sand. Grain crushing within the shear zone was examined. Finally, it was found that there was an optimal density at which the undrained brittleness index had a minimum value; meanwhile, the undrained brittleness index became greater with increasing initial normal and shear stresses, but decreased with shear times. These findings offer some basic understanding in assessing the postfailure mobility in landslides.Key words: excess pore pressure, localized liquefaction, shear resistance, ring-shear tests, grain crushing, silty sands.
The Eureka River landslide and dam, Peace River Lowlands, Alberta
Authors: Miller B G.N , Cruden D M
Published: October 2002

The Eureka River landslide of June 1990, at 50 Mm3, is one of the largest historical landslides on the Interior Plains of Canada. It is one of seven large translational landslides to have occurred in the Peace River Lowlands within the last 65 years. Each landslide occurred in Quaternary sediments deposited within a preglacial valley. Each landslide formed a dam. The rupture surface of the Eureka River landslide in preglacial lacustrine sediment, 125 m below the Peace River Lowlands plains, extended beneath the river channel causing the channel to be elevated. The resulting landslide dam was over 20 m high, forming a lake exceeding 8 km in length. The river cut a new channel around the toe of the landslide, abandoning the prelandslide channel. As the new channel is free of armour, incision has been rapid. After 10 years, the dam now stands approximately 5 m high.Key words: landslide, landslide dam, Peace River, Alberta, preglacial valley, geomorphology.
Plasmid-borne AmpC β-lactamases
Authors: Walther-Rasmussen Jan , Høiby Niels
Published: October 2002

Historically, it was thought that ampC genes encoding class C β-lactamases were located solely on the chromosome but, within the last 12 years, an increasing number of ampC genes have been found on plasmids. These have mostly been acquired by ampC-deficient pathogenic bacteria, which consequently are supplied with new and additional resistance phenotypes. This review discusses the phylogenetic origin of the plasmid-encoded AmpC β-lactamases, their occurrence, and mode of spread, as well as their hydrolytic properties.Key words: AmpC β-lactamases, plasmid-encoded, phylogeny, dissemination.
Biofilm formation in drinking water affected by low concentrations of phosphorus
Authors: Lehtola Markku J , Miettinen Ilkka T , Martikainen Pertti J
Published: October 2002

There are geographical regions where microbial growth in drinking waters is limited by phosphorus instead of organic carbon. In these drinking waters even a low amount of phosphorus can strongly enhance microbial growth. The formation of biofilm can be limited by low availability of phosphorus in drinking waters with low content of phosphorus. The formation of biofilms on polyvinyl chloride plates was studied in laboratory experiments with water containing 48 μg/L assimilable organic carbon and 0.19 μg/L microbially available phosphorus. We found that low additions of phosphate (15 μg/L PO43-P) to water increased microbial growth in the water and in the biofilm. The effect of phosphorus on microbial growth could be detected by determining either the microbial cell production or the content of ATP in biofilms. Also, in steady-state biofilms, microbial concentrations were higher with phosphorus addition as enumerated by heterotrophic plate counts on R2A-agar and acridine orange direct counting. This work confirms the earlier findings of the importance of phosphorus for microbial growth in humic-rich drinking waters.Key words: biofilm, drinking water, microbes, phosphorus.
The effects of fungicides on the phylloplane yeast populations of creeping bentgrass
Authors: Buck James W , Burpee Leon L
Published: October 2002

The effects of fungicides on population size and the development of fungicide resistance in the phylloplane yeast flora of bentgrass was investigated. In the spring of 2001, azoxystrobin, chlorothalonil, flutolanil, and propiconazole were applied separately over a 6-week period to creeping bentgrass (Agrostis palustris Huds.). Total and fungicide-resistant yeast populations were assessed by dilution plating onto either potato dextrose agar or potato dextrose agar amended with the test fungicides. Total yeast populations in the fungicide- treated plots were significantly lower than the check plots on three out of four sample dates. In the fall, azoxystrobin or propiconazole were applied twice to the bentgrass over 3 weeks. Significantly larger total yeast populations were observed compared with resistant or highly resistant populations for each treatment on every sample date. Total yeast populations were significantly higher in the check plots compared with either the propiconazole- or azoxystrobin-treated plots on the first three of five sample dates. A collection of yeasts (N = 114) with no prior exposure to fungicides were more sensitive to chlorothalonil, propiconazole, flutolanil, and iprodione than a second group (N = 115) isolated from fungicide-treated turfgrass. These results suggest that fungicide resistance among phylloplane yeasts is widespread and could be an important factor in the development of biological control agents for turfgrass diseases.Key words: yeast, biological control, fungicide, resistance, phylloplane.
Actinobacillus actinomycetemcomitansgenetic heterogeneity: amplification of JP2-likeltxpromoter pattern correlated with specific arbitrarily primed polymerase chain reaction (AP-PCR) genotypes from human but not marmoset Brazilian isolates
Authors: Saddi-Ortega L , Carvalho M A.R , Cisalpino P S , Moreira E S.A
Published: October 2002

Specific clonal types of Actinobacillus actinomycetemcomitans, a major human periodontal pathogen, may be responsible for clinical manifestations and the production of leukotoxin virulence factors. Leukotoxicity is associated with genetic polymorphism at the promoter region of the leukotoxin (ltx) gene. Here, we describe the use of arbitrarily primed polymerase chain reaction (AP-PCR) and ltx promoter PCR to molecularly characterise 35 A. actinomycetemcomitans Brazilian isolates: 21 of human origin and 14 from captive marmosets (Callitrix spp., primates commonly used as animal models for periodontal research). The discriminative capacity of each of 12 arbitrary primers was found to be variable, yielding between 3 and 24 PCR amplitypes. Combination of the results for all primers led to characterisation of 14 genotypes that grouped into four major clusters based on genetic similarity. Clusters 2, 3, and 4 were discriminative to host origin. A correlation with periodontal disease was suggested for strains belonging to clusters 3 and 4. The JP2-like PCR amplification pattern, associated with highly leukotoxic strains, was exclusive to human isolates and present in 29% of human isolates where it occurred in close relationship with AP genotypes L and J (cluster 3).Key words: Actinobacillus actinomycetemcomitans, marmosets, AP-PCR, leukotoxin.
Rates of litter decomposition over 6 years in Canadian forests: influence of litter quality and climate
Authors: Trofymow J A , Moore T R , Titus B , Prescott C , Morrison I , Siltanen M , Smith S , Fyles J , Wein R , Camiré C , Duschene L , Kozak L , Kranabetter M , Visser S
Published: October 2002

The effects of litter quality and climate on decomposition rates of plant tissues were examined using percent mass remaining (MR) data of 10 foliar litter types and 1 wood type during 6 years exposure at 18 upland forest sites across Canada. Litter-quality variables used included initial nutrient contents (N, P, S, K, Ca, Mg) and carbon fractions (determined by proximate analysis and 13C nuclear magnetic resonance spectroscopy). Climate variables used included mean annual temperature; total, summer, and winter precipitation; and potential evaptranspiration. A single-exponential decay model with intercept was fit using the natural logarithm of 0- to 6-year percent MR data (LNMR) for all 198 type by site combinations. Model fit was good for most sites and types (r2 = 0.640.98), although poorest for cold sites with low-quality materials. Multiple regression of model slope (Kf) and intercept (A) terms demonstrated the importance of temperature, summer precipitation, and the acid-unhydrolyzable residue to N ratio (AUR/N) (r2 = 0.65) for Kf, and winter precipitation and several litter-quality variables including AUR/N for A (r2 = 0.60). Comparison of observed versus predicted LNMR for the best overall combined models were good (r2 = 0.750.80), although showed some bias, likely because of other site- and type-specific factors as predictions using 198 equations accounted for more variance (r2 = 0.95) and showed no bias.
Résistance comparée de l'épinette blanche et du sapin baumier au renversement
Authors: Meunier S , Ruel J -C , Laflamme G , Achim A
Published: October 2002

Information on eastern Canadian tree species vulnerability to windthrow is scarce. Some statements on relative species vulnerability have been made but they rely on empirical observations, which are often difficult to generalize. In this context, a study was conducted to compare the overturning resistance of balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss) on a mesic site. To establish which tree characteristics would best explain the critical turning moment, simple linear regressions were calculated using tree dendrometric data. The best regressions were obtained with stem weight. With this variable, resistance to overturning did not differ between the two species. Only regressions involving total height showed a significantly greater resistance for white spruce. This difference can be explained by a difference between the species in heightdiameter relationships. For a similar height, spruce has a greater diameter, involving a higher stem weight and thus a greater resistance. Decay did not play a major role in our experiment as trees with external defects were excluded. Our results suggest that to minimize losses from windthrow, silvi cultural treatments on mesic sites should try to increase the proportion of trees of either species with the lowest height/diameter ratio.
Aboveground biomass and nutrient accumulation 20 years after clear-cutting a southern Appalachian watershed
Authors: Elliott Katherine J , Boring Lindsay R , Swank Wayne T
Published: October 2002

In 1975, we initiated a long-term interdisciplinary study of forest watershed ecosystem response to clear-cutting and cable logging in watershed 7 at the Coweeta Hydrologic Laboratory in the southern Appalachian Mountains of North Carolina. This paper describes [Formula: see text]20 years of change in species composition, aboveground biomass, leaf area index (LAI), and nutrient pools in the 59-ha mixed hardwood forest of watershed 7 following commercial clear-cutting in winter 1977. We measured woody species in 24 permanently marked plots before cutting in 1974 and during subsequent years (19771997). By 1997 ([Formula: see text]20 years after cutting), aboveground biomass was 81.7, 96.9, and 85.4 Mg·ha1in the cove hardwood; mesic, mixed-oak; and dry, mixed-oak communities, respectively. Leaf biomass and LAI accumulated relatively faster than total aboveground biomass in all three communities. By 1984, only 78 years after cutting, leaf biomass and LAI were nearly equal to the amount estimated for the precut forest. In 1997, nitrogen accumulation was 36, 44, and 61% and phosphorus accumulation was 48, 66, and 59% in the cove-hardwoods; mesic, mixed-oak; and dry, mixed-oak communities of the corresponding precut communities, respectively. Potassium, calcium, and magnesium accumulations were less than either nitrogen or phosphorus accumulation.
NOTEGypsy moth defoliation and N fertilization affect hybrid poplar regeneration following coppicing
Authors: Agrawal Anurag A , Kosola Kevin R , Parry Dylan
Published: October 2002

The interaction between insect outbreaks and forest health or tree plantation management has been considered rarely from an experimental approach. From 1996 to 1998, we experimentally created a gypsy moth outbreak that defoliated large plots of mature hybrid poplars, Populus ×euramericana, with half of the plots fertilized in a factorial design. The trees were harvested at rotation age in 1999, and we examined the mortality and regeneration of the coppiced (cut at the base) trees in the following growing season. Pre-treatment estimates of tree size strongly predicted the mortality and number of regenerating stems following harvest but not the height of those stems. Defoliation and fertilization each modestly increased tree mortality (10 and 6%, respectively), but the effects were not additive. Only defoliation had strong residual effects on the surviving trees: 25% fewer resprouting stems were produced by previously defoliated trees compared to undefoliated control trees.
Pine needle rust effect on Pinus banskiana in response to interspecific plant competition and telial host density
Authors: Mihail J D , Bruhn J N , Meyer T R , Bell F W
Published: October 2002

Three compartments differing in soil texture were established in 1994 to examine interspecific competition using Pinus banskiana Lamb. and 11 competitive species including Aster macrophyllus L. Each competitive species was established in six planting densities in combination with P. banksiana. Since P. banksiana and A. macrophyllus are hosts of the pine needle rust (PNR) fungus, Coleosporium asterum (Diet.) Syd., conditions were inadvertently created for examining the effect of PNR on tree growth under interspecific competition. Tree size was measured in 1995 and 1996. PNR was assessed in 1996 (incidence) and 1997 (severity). Pinus banksiana root collar diameter, stem length, and crown diameter were significantly lower in the loam soil texture compartment compared with the clay or sand compartments. Using the same metrics, P. banksiana size was reduced as competitor density increased in 1995 and 1996, particularly for A. macrophyllus. Further, P. banksiana size was significantly reduced by PNR infection in 1996. Excluding the plots with A. macrophyllus, P. banksiana infected in 1996 were significantly larger than disease-free trees in the clay and sand compartments, suggesting that larger trees may represent larger targets for spore deposition. In 1996, PNR incidence was significantly correlated with proximity to A. macrophyllus plots.
Recruitment of wood to streams in old-growth and second-growth redwood forests, northern California, U.S.A.
Authors: Benda Lee E , Bigelow Paul , Worsley Thomas M
Published: October 2002

From an ecological perspective, one aim of forest management is to supply wood to streams to protect and enhance aquatic habitats. An analysis was made of the mass balance of in-stream wood along 9 km of channels in old-growth and 50-year-old second-growth redwood (Sequoia sempervirens (D. Don) Endl.) forests in northern California, U.S.A. High volumes of wood storage in streams in old-growth forests were due primarily to streamside landsliding and bank erosion. Logging-related debris and high forest mortality rates in conifer and deciduous forests contributed to high wood storage in second-growth forests. Volumes of in-stream wood in second-growth forests were similar to volumes in one old-growth system and less than another. Diameters of wood were significantly greater in older forests. Wood recruitment from forest mortality in old-growth forests was low compared with second-growth sites, driven by differences in conifer mortality rates of approximately 0.04 and 0.9%·year1, respectively. Contrasting old-growth redwood mortality with values reported for unmanaged Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in Washington State (0.5%·year1) and unmanaged Sitka spruce (Picea stichensis (Bong.) Carrière) forests in southeastern Alaska (1.2%·year1) point to a strong latitudinal gradient of forest mortality reflected in tree size. The mass balance analysis of in-stream wood also allowed an estimation of bank erosion along large channels and soil creep along small, steep streams.
A DYNAMICS RECOMMENDATION SYSTEM BASED ON LOG MINING
Authors: GAO WEN , WANG SHI , LIU BIN
Published: October 2002

This paper presents a new real-time, dynamic web page recommendation system based on web-log mining. The visit sequences of previous visitors are used to train a classifier for web page recommendation. The recommendation engine identifies a current active user, and submits its visit sequence as an input to the classifier. The output of the recommendation engine is a set of recommended web pages, whose links are attached to bottom of the requested page. Our experiments show that the proposed approach is effective: the predictive accuracy is quite high (over 90%), and the time for the recommendation is quite small.
APPROXIMATION ALGORITHMS FOR SCHEDULING MALLEABLE TASKS UNDER PRECEDENCE CONSTRAINTS
Authors: LEPÈRE RENAUD , TRYSTRAM DENIS , WOEGINGER GERHARD J.
Published: October 2002

This work presents approximation algorithms for scheduling the tasks of a parallel application that are subject to precedence constraints. The considered tasks are malleable which means that they may be executed on a varying number of processors in parallel. The considered objective criterion is the makespan, i.e., the largest task completion time. We demonstrate a close relationship between this scheduling problem and one of its subproblems, the allotment problem. By exploiting this relationship, we design a polynomial time approximation algorithm with performance guarantee arbitrarily close to [Formula: see text] for the special case of series parallel precedence constraints and for the special case of precedence constraints of bounded width. These special cases cover the important situation of tree structured precedence constraints. For arbitrary precedence constraints, we give a polynomial time approximation algorithm with performance guarantee [Formula: see text].
ON RICCI RANK OF CARTAN–HADAMARD MANIFOLDS
Authors: GULER DINCER , ZHENG FANGYANG
Published: October 2002

In this article, we prove that the maximum rank r of the Ricci tensor of a Cartan–Hadamard manifold Mn satisfies the inequality 2r - 1 ≥ n - s, where n is the dimension and s is the core number, which measures the flatness of Mn. Examples show that this lower bound is sharp.
GLASS TRANSITION IN THIN POLYMER FILMS: A MOLECULAR DYNAMICS STUDY
Authors: VARNIK FATHOLLAH , BINDER KURT , BASCHNAGEL JÖRG
Published: October 2002

A melt of nonentangled polymer chains confined between two smooth and purely repulsive walls is studied for various film thicknesses D and temperatures. The dynamics of the supercooled films is qualitatively identical to that of the bulk, but the walls lead to faster relaxation. To quantify this observation we analyze the data by the mode-coupling theory (MCT) of the glass transition. We find that the critical temperature of MCT, Tc(D), decreases with D and that T - Tc(D) is a relevant temperature scale. The static structure factor and dynamic correlation functions at intermediate times coincide with bulk behavior when compared to the same T - Tc(D).
TESTING THE CACTUS CODE ON EXACT SOLUTIONS OF THE EINSTEIN FIELD EQUATIONS
Authors: VULCANOV DUMITRU N. , ALCUBIERRE MIGUEL
Published: October 2002

The article presents a series of numerical simulations of exact solutions of the Einstein equations performed using the Cactus code, a complete three-dimensional machinery for numerical relativity. We describe an application ("thorn") for the Cactus code that can be used for evolving a variety of exact solutions, with and without matter, including solutions used in modern cosmology for modeling the early stages of the universe. Our main purpose has been to test the Cactus code on these well-known examples, focusing mainly on the stability and convergence of the code.
VELOCITY DISTRIBUTION IN THE DUKE–RUBINSTEIN MODEL
Authors: PAŚCIAK P. , KRAWCZYK M. J. , KUŁAKOWSKI K.
Published: October 2002

The Duke–Rubinstein model of gel electrophoresis is applied to calculate the velocity of DNA molecules. We have found that the velocity distribution becomes flat at high electric fields. Simultaneously, the percentage of immobile molecules increases. Effectively, the mean velocity starts to decrease at high fields. The field value, where the mean velocity is maximal, decreases with the molecule length. The results are compared with those from similar calculations obtained by Heukelum and Beljaars within the cage model.
ROTATING BRANE WORLD BLACK HOLES
Authors: MODGIL MONINDER SINGH , PANDA SUKANTA , SENGUPTA GAUTAM
Published: October 2002

A five-dimensional rotating black string in a Randall–Sundrum brane world is considered. The black string intercepts the three-brane in a four-dimensional rotating black hole. The geodesic equations and the asymptotics in this background are discussed.
THE MULTI-VALUE OF EFFECTIVE NUCLEON MASS IN HOT/DENSE NUCLEAR MATTER AND THE PHASE TRANSITION
Authors: JIN MENG , LI JIARONG , CHEN JISHENG
Published: October 2002

From the Lagrangian of QHD-I model, we investigate the effective nucleon mass under the mean field approximation in a wide temperature region. The multi-solution of self-consistent equation for the effective mass in found. In the high temperature region, the relation between the multi-solutions and the phase transition is analyzed. Furthermore, the variation of energy density in this region is studied.
CP VIOLATION IN THE DECAY η → π+ π- γ
Authors: GENG C. Q. , NG J. N. , WU T. H.
Published: October 2002

We study the CP violating effects in the decay of η → π+π- γ. We show that to have CP violation in the decay, one has to consider both linear and circular photon polarizations. In the standard model, the polarizations are vanishingly small. However, model independently, i.e. using only experimental constraint imposed by the limit on Br (η → π+ π-), it can be up to O(10%). We also explore various possible operators and we find that the tensor type operator, possibly arising from a nonzero CP violating electric dipole moment of the strange quark, can induce a sizable linear photon polarization.