bluuebunny/crossref_metadata_2025 huggingface dataset:
How does the European eel (Anguilla anguilla) retain its population structure during its larval migration across the North Atlantic Ocean?
Authors: Kettle A James , Haines Keith
Published: January 2006

A Lagrangian model is presented of the current-carried migration of the leptocephali (larvae) of the European eel (Anguilla anguilla) across the North Atlantic Ocean from the spawning area in the Sargasso Sea to the adult range in Europe and North Africa. The success of larvae in crossing the Atlantic Ocean and reaching particular latitude bins on the eastern side depended strongly on starting location in the Sargasso Sea and migration depth. In the model domain, silver eel spawners can develop strategies for spawning location and migration depth to preferentially target particular regions in the adult range. This observation may help to explain the presence of gradients in molecular markers in eel samples collected across Europe. Spawning in the period of late winter  spring maximizes the average food availability along the 2-year larval trajectory. The fastest transatlantic larval migration in the model is about 2 years, and the route to Europe takes most of the larvae past the east coast of North America in the first year. These model results are consistent with the hypothesis that the European and American eel (Anguilla rostrata) could separate themselves on different sides of the Atlantic Ocean on the basis of the different durations of their larval stages.
Effects of rifflestep restoration on hyporheic zone chemistry in N-rich lowland streams
Authors: Kasahara Tamao , Hill Alan R
Published: January 2006

Stream restoration projects that aim to rehabilitate ecosystem health have not considered surfacesubsurface linkages, although stream water and groundwater interaction has an important role in sustaining stream ecosystem functions. The present study examined the effect of constructed riffles and a step on hyporheic exchange flow and chemistry in restored reaches of several N-rich agricultural and urban streams in southern Ontario. Hydrometric data collected from a network of piezometers and conservative tracer releases indicated that the constructed riffles and steps were effective in inducing hyporheic exchange. However, despite the use of cobbles and boulders in the riffle construction, high stream dissolved oxygen (DO) concentrations were depleted rapidly with depth into the hyporheic zones. Differences between observed and predicted nitrate concentrations based on conservative ion concentration patterns indicated that these hyporheic zones were also nitrate sinks. Zones of low hydraulic conductivity and the occurrence of interstitial fines in the restored cobble-boulder layers suggest that siltation and clogging of the streambed may reduce the downwelling of oxygen- and nitrate-rich stream water. Increases in streambed DO levels and enhancement of habitat for hyporheic fauna that result from rifflestep construction projects may only be temporary in streams that receive increased sediment and nutrient inputs from urban areas and croplands.
Does the river continuum concept apply on a tropical island? Longitudinal variation in a Puerto Rican stream
Authors: Greathouse Effie A , Pringle Catherine M
Published: January 2006

We examined whether a tropical stream in Puerto Rico matched predictions of the river continuum concept (RCC) for macroinvertebrate functional feeding groups (FFGs). Sampling sites for macroinvertebrates, basal resources, and fishes ranged from headwaters to within 2.5 km of the fourth-order estuary. In a comparison with a model temperate system in which RCC predictions generally held, we used catchment area as a measure of stream size to examine truncated RCC predictions (i.e., cut off to correspond to the largest stream size sampled in Puerto Rico). Despite dominance of generalist freshwater shrimps, which use more than one feeding mode, RCC predictions held for scrapers, shredders, and predators. Collectorfilterers showed a trend opposite to that predicted by the RCC, but patterns in basal resources suggest that this is consistent with the central RCC theme: longitudinal distributions of FFGs follow longitudinal patterns in basal resources. Alternatively, the filterer pattern may be explained by fish predation affecting distributions of filter-feeding shrimp. Our results indicate that the RCC generally applies to running waters on tropical islands. However, additional theoretical and field studies across a broad array of stream types should examine whether the RCC needs to be refined to reflect the potential influence of top-down trophic controls on FFG distributions.
The effect of selenium on mercury assimilation by freshwater organisms
Authors: Belzile Nelson , Chen Yu-Wei , Gunn John M , Tong Jian , Alarie Yves , Delonchamp Tania , Lang Chun-Yan
Published: January 2006

In this study, we showed that selenium (Se) deposition from metal smelters in Sudbury, Ontario, greatly re duces the bioassimilation of mercury (Hg) by aquatic biota throughout the food web. Concentrations of total and methyl mercury in tissues of zooplankton, mayflies (Stenonema femoratum), amphipods (Hyalella azteca), and young-of-the-year perch (Perca flavescens) were positively correlated with increasing distance from Sudbury smelters and inversely correlated with Se concentrations in lake water. Although concentrations of total Hg and total Se in tissues showed weak or no correlation in most of the studied aquatic species, methyl mercury and total Se showed much clearer inverse trends. Similar to the results of our previous study of muscle tissue from adult perch and walleye (Sander vitreus), these findings suggest that Se plays an important role in limiting the whole-body assimilation of Hg at lower levels of the aquatic food chain. High Se concentrations may force a preferential assimilation of the element over Hg through a competitive adsorption on binding sites. They may also restrict the solubility and availability of Hg to aquatic organisms or reduce the methylation of this metal in lakes.
Distribution, abundance, and diversity of stream fishes under variable environmental conditions
Authors: Taylor Christopher M , Holder Thomas L , Fiorillo Riccardo A , Williams Lance R , Thomas R Brent , Warren, Jr. Melvin L
Published: January 2006

The effects of stream size and flow regime on spatial and temporal variability of stream fish distribution, abundance, and diversity patterns were investigated. Assemblage variability and species richness were each significantly associated with a complex environmental gradient contrasting smaller, hydrologically variable stream localities with larger localities characterized by more stable flow regimes. Assemblages showing the least variability were the most species-rich and occurred in relatively large, stable environments. Theory suggests that species richness can be an important determinant of assemblage variability. Although this appears to be true in our system, we suggest that spatial and temporal heterogeneity in the environment largely determines both assemblage richness and variability, providing a more parsimonious explanation for the diversityvariability correlation. Changes in species richness of local assemblages across time were coordinated across the landscape, and assemblages formed spatially and temporally nested subset patterns. These results suggest an important link between local community dynamics and community-wide occurrence. At the species level, mean local persistence was significantly associated with regional occurrence. Thus, the more widespread a species was, the greater its local persistence. Our results illustrate how the integrity of local stream fish assemblages is dependent on local environmental conditions, regional patterns of species distribution, and landscape continuity.
Effectiveness of marine reserves for large-scale fisheries management
Authors: Smith Martin D , Zhang Junjie , Coleman Felicia C
Published: January 2006

As more no-take marine reserves are established, the importance of evaluating effectiveness retrospectively is growing. This paper adapts methods from program evaluation to quantify the effects of establishing a marine reserve on fisheries using fishery-dependent data. The approach analyzes the effects of a policy at the individual vessel level and accommodates the coarse spatial resolution of fishing logbooks. It illuminates implicit assumptions in previous retrospective analyses of marine reserves that are unlikely to hold for large-scale fisheries. We illustrate the empirical model with an application to the Gulf of Mexico reef-fish fishery. Isolating the effects of reserves requires a full accounting of multiple gear production technologies, heterogeneity in vessel captain skill, spatial heterogeneity of fish stocks, seasonal patterns in abundance, the effects of coexisting management policies, and the possibility that the harvest sector anticipates reserve establishment. We find that the effect of two recently established marine reserves on catch is negative and trending downward, though the reserves have only been in place for 4.5 years.
Have brook trout (Salvelinus fontinalis) displaced bull trout (Salvelinus confluentus) along longitudinal gradients in central Idaho streams?
Authors: Rieman Bruce E , Peterson James T , Myers Deborah L
Published: January 2006

Invasions of non-native brook trout (Salvelinus fontinalis) have the potential for upstream displacement or elimination of bull trout (Salvelinus confluentus) and other native species already threatened by habitat loss. We summarized the distribution and number of bull trout in samples from 12 streams with and without brook trout in central Idaho and used hierarchical regression analysis to consider whether brook trout have displaced bull trout along gradients of temperature and elevation. Brook trout generally were observed in higher numbers downstream of bull trout. Brook trout presence, number, and both temperature and elevation were important variables explaining the observed distributions and number of bull trout among streams. Our analyses support the hypothesis that brook trout have displaced bull trout, but results were highly variable and stream dependent. Although brook trout appeared to have displaced bull trout to higher elevations or colder temperatures, there was no clear influence on overall number of bull trout. Brook trout probably do influence bull trout populations and facilitate if not cause local extinctions, but threats probably vary strongly with environmental conditions. Bull trout in smaller streams could be more vulnerable than those in larger streams.
State-dependent energy allocation in cod (Gadus morhua)
Authors: Jørgensen Christian , Fiksen Øyvind
Published: January 2006

Growth and maturation are processes that are tuned to the external environment that an individual is likely to experience, where food availability, the mortality regime, and events necessary to complete the life cycle are of special importance. Understanding what influences life history strategies and how changes in life history in turn influence population dynamics and ecological interactions are crucial to our understanding of marine ecology and contemporary anthropogenic induced change. We present a state-dependent model that optimises life-long energy allocation in iteroparous fish. Energy can be allocated to growth or reproduction and depends in the individual's age, body length, and stored energy and the state of the environment. Allocation and the physiological processes of growth, energy storage, and reproduction are modelled mechanistically. The model is parameterised for Atlantic cod (Gadus morhua), more specifically the Northeast Arctic cod stock. Growth and maturation predicted by the model fit well with field observations, and based on a further investigation of cod reproduction in the model, we conclude that the model has the ability to recapture complex life history phenomena, e.g., indeterminate growth and skipped spawning, and therefore provides an important tool that can improve our understanding of life history strategies in fish.
A Bayesian statespace markrecapture model to estimate exploitation rates in mixed-stock fisheries
Authors: Michielsens Catherine G.J , McAllister Murdoch K , Kuikka Sakari , Pakarinen Tapani , Karlsson Lars , Romakkaniemi Atso , Perä Ingemar , Mäntyniemi Samu
Published: January 2006

A Bayesian statespace markrecapture model is developed to estimate the exploitation rates of fish stocks caught in mixed-stock fisheries. Expert knowledge and published results on biological parameters, reporting rates of tags and other key parameters, are incorporated into the markrecapture analysis through elaborations in model structure and the use of informative prior probability distributions for model parameters. Information on related stocks is incorporated through the use of hierarchical structures and parameters that represent differences between the stock in question and related stocks. Fishing mortality rates are modelled using fishing effort data as covariates. A statespace formulation is adopted to account for uncertainties in system dynamics and the observation process. The methodology is applied to wild Atlantic salmon (Salmo salar) stocks from rivers located in the northeastern Baltic Sea that are exploited by a sequence of mixed- and single-stock fisheries. Estimated fishing mortality rates for wild salmon are influenced by prior knowledge about tag reporting rates and salmon biology and, to a limited extent, by prior assumptions about exploitation rates.
Predator communities associated with brook stickleback (Culaea inconstans) prey: patterns in body size
Authors: Zimmerman Mara S
Published: January 2006

Prey body size is often inversely correlated with largest size of coexisting predators, yet few studies have examined this relationship in the context of entire predator communities. Using field surveys and laboratory trials, this study tested whether a size relationship exists between brook stickleback (Culaea inconstans) prey and the largest coexisting predator in the context of nested predator communities at 26 sites across Michigan's upper peninsula. Small predators, limited to consuming small sticklebacks, were widely distributed and equally common in pond, breached pond, and stream habitats. Large predators consumed all stickleback sizes, occurred at fewer sites, and were found more frequently in stream than in pond and breached pond habitats in one of the two survey years. Predator communities were categorized as small-predator and mixed-predator communities. Small-predator communities included small, gape-limited predators only. Sticklebacks apparently reached a size refugia from predation (>42 mm standard length) in this community type. Mixed-predator communities included both small and large predators and had no size refugia for sticklebacks. Although predator distributions were nested in this system, prey size was correlated with the largest predator size at each site. Stickleback length was negatively correlated with maximum predator length and was smaller in mixed-predator than in small-predator communities.
Using bioenergetics and stable isotopes to assess the trophic role of rusty crayfish (Orconectes rusticus) in lake littoral zones
Authors: Roth Brian M , Hein Catherine L , Vander Zanden M Jake
Published: January 2006

Crayfish often dominate freshwater ecosystems and can have strong effects on littoral habitat and biota through foraging. However, there is substantial debate regarding the trophic role of crayfish and implications of their foraging behavior on littoral ecosystems. We created a bioenergetics model for rusty crayfish (Orconectes rusticus) to determine how growth and prey choice constrain crayfish consumption, which affects littoral ecosystems. We simulated over 6400 potential rusty crayfish diets by varying the abundance of important prey. We judged how crayfish prey choice affects the amount and identity of prey that crayfish must consume to match observed growth. We compared our model predictions with stable isotope evidence from 10 northern Wisconsin lakes to determine energy sources and trophic position of rusty crayfish relative to other invertebrates. Our diet simulations and stable isotope analysis concurred that crayfish of all ages are primarily predators. Individuals that do not feed on zoobenthos must therefore consume large quantities of less desirable food such as macrophytes, which are an important component of littoral habitat.
Variable uptake and elimination of stable nitrogen isotopes between tissues in fish
Authors: MacNeil M Aaron , Drouillard Ken G , Fisk Aaron T
Published: January 2006

We conducted a diet-switching experiment using freshwater ocellate river stingrays (Potamotrygon motoro) fed a novel earthworm (Eisenia foetida) diet to establish the relative contributions of growth and metabolism to δ15N values in an elasmobranch species. We specifically controlled for the potential effects of protein composition of experimental diets on δ15N turnover to determine whether δ15N turnover after a low to high δ15N diet switch (uptake) and a high to low δ15N diet switch (elimination) will occur at the same rate within each consumer tissue. Our results showed that the turnover of δ15N from metabolism and growth differed between uptake and elimination phases in the liver, blood, cartilage, and muscle of freshwater stingrays. During uptake, liver was found to track dietary δ15N more closely than the other tissues, with the highest metabolic turnover rate of δ15N (0.015 day1), whereas cartilage had the slowest rate of metabolic δ15N turnover (0.0022 day1) relative to a constant rate of growth among tissues (0.003 day1). We propose that estimates of trophic position from muscle sampling alone have considerable uncertainty, particularly for scavenging or omnivorous species. We suggest that multitissue sampling can identify this problem and lead to a more robust evaluation of trophic dynamics for individual species.
Development and use of the Wetland Fish Index to assess the quality of coastal wetlands in the Laurentian Great Lakes
Authors: Seilheimer T S , Chow-Fraser P
Published: January 2006

We use fish and environmental data from 40 wetlands of the Laurentian Great Lakes to develop the Wetland Fish Index (WFI), a tool that can be used to assess the quality of coastal marshes. A partial canonical correspondence analysis was used to ordinate fish species along multidimensional environmental axes that accounted for anthropogenic disturbance based on temperature, conductivity, and the presence of pollutants (e.g., suspended solids and primary nutrients). Compared with other measures of fish habitat quality (e.g., ShannonWiener diversity index and species richness), the WFI was the only index that was significantly related to the degree of water quality degradation and wetlands condition, as indicated by an independent index of wetland quality, the Water Quality Index (WQI). WQI ranks sites according to deterioration in water quality and is statistically related to the degree of land-use alteration in wetland watersheds. We demonstrate the usefulness of the WFI for detecting intrawetland variation between two sites in a degraded urban wetland, Frenchman's Bay, Lake Ontario, and to distinguish the heavily impacted wetlands in lower Green Bay from the less-impacted marshes in middle and upper Green Bay, Lake Michigan. This was accomplished by using only published fish data without corresponding environmental variables.
Chutes and ladders and other games we play with rivers. I. Simulated effects of upstream passage on white sturgeon
Authors: Jager Henriette I
Published: January 2006

River fragmentation by dams has often preceded declines in sturgeon populations, which suggests that reconnecting populations would contribute to their recovery. This study used a population viability model to quantify the effects of upstream passage at dams on white sturgeon (Acipenser transmontanus) metapopulations inhabiting a series of long (source) and short (sink) river segments. Simulated river systems with high interspersion of long and short segments and a long segment far upstream supported the healthiest metapopulations, suggesting biological criteria for siting dams. Contrary to expectation, the model predicted that upstream passage, without screening or downstream passage, was harmful to the metapopulation as a whole. However, upstream passage was beneficial when downstream migration was either restricted (by screening larger fish) or made safe (by providing downstream passage). The combination of upstream and downstream passage was most beneficial at dams above a long river segment. Screening, alone or combined with upstream passage, was most beneficial at dams below a long segment. These theoretical results highlight the need for field research to evaluate management options and provide practical guidance for restoring sturgeon metapopulations in large rivers.
An evaluation of the Clearwater River supplementation program in western Washington
Authors: Sharma Rishi , Morishima Gary , Wang Shizhen , Talbot André , Gilbertson Larry
Published: January 2006

This paper presents preliminary results of a study to evaluate the potential utility of supplementation of natural origin coho salmon (Oncorhynchus kisutch) on the Clearwater River, a tributary of the Queets River in western Washington. The study, initiated in 1984, involves the collection of natural origin brood stock, rearing in a combination of hatchery and natural environments, and volitional releases, combined with marking and sampling of natural origin fish. Primary findings relative to five essential research questions of this study concluded that (i) smolts from supplementation returned at a lower rate than natural smolts; (ii) the reproductive efficiency (spawner to spawner) of fish taken for supplementation was higher than that for fish allowed to spawn naturally; (iii) supplemental fish successfully reproduced and the combined supplementalnatural spawning population had a high productivity; (iv) supplementation did not appear to have affected the overall reproductive performance of the population for the duration of the project; and (v) supplementation increased the overall spawner return on the Clearwater River and is required to maximize adult production, unless conditions in both freshwater and ocean environments are optimal.
The role of semiochemicals in host location and non-host avoidance by salmon louse (Lepeophtheirus salmonis) copepodids
Authors: Bailey Roberta JE , Birkett Michael A , Ingvarsdóttir Anna , Mordue (Luntz) A Jennifer , Mordue William , O'Shea Bríd , Pickett John A , Wadhams Lester J
Published: January 2006

The role and identity of host and non-host chemical cues (semiochemicals) in host location and non-host avoidance for copepodid larvae of sea lice, Lepeophtheirus salmonis, was investigated using Y-tube behavioural bioassays, solid-phase extraction (SPE), and coupled gas chromatography  mass spectrometry (GCMS). Using artificial seawater conditioned with the preferred salmonid host, Salmo salar, L. salmonis displayed high activation and directional responses in Y-tube assays to salmon-conditioned water (SCW), to an extract of SCW prepared by SPE, and to a vacuum distillate of the SPE extract. Similar responses were observed to two chemicals identified from SCW by coupled GCMS: isophorone and 6-methyl-5-hepten-2-one. Dose-response studies with isophorone showed that copepodid responses across the range tested were maximised at 0.01 and 0.1 mg·mL1. A mixture of isophorone and 6-methyl-5-hepten-2-one also induced high activation and directional responses. Semiochemicals were also isolated from the non-host fish, turbot (Scophthalmus maximus (Rafinesque)), by SPE and analysed by GCMS. Two non-host-specific chemicals were identified as 2-aminoacetophenone and 4-methylquinazoline. When SCW was mixed with either of the non-host chemicals, activation and directional responses to SCW were eliminated in the Y tube.
Fireproof killer whales (Orcinus orca): flame-retardant chemicals and the conservation imperative in the charismatic icon of British Columbia, Canada
Authors: Ross Peter S
Published: January 2006

Long-lived and high trophic level marine mammals are vulnerable to accumulating often very high concentrations of persistent chemicals, including pesticides, industrial by-products, and flame retardants. In the case of killer whales (Orcinus orca), some of the older individuals currently frequenting the coastal waters of British Columbia (BC) were born during the First World War, well before the advent of widespread chemical manufacture and use. BC's killer whales are now among the most polychlorinated biphenyl (PCB) contaminated marine mammals in the world. While the "legacy" PCBs have largely been banned, polybrominated diphenyl ethers (PBDEs) have recently emerged as a major concern. The endocrine-disrupting nature of these two persistent fire retardants in biota spells trouble at the top of the food chain, with increasing evidence of effects on reproductive health, the immune system, and development in exposed mammals. The heavy contamination of BC's killer whales, coupled with their long life span and high trophic level, highlights the need for a "weight of evidence" approach in research, conservation planning, and regulatory decisions. Given the global nature of contaminant dispersion, such approaches can only be effective when carried out on both national and international scales.
Fishing under low productivity conditions is further delaying recovery of Northwest Atlantic cod (Gadus morhua)
Authors: Shelton Peter A , Sinclair Alan F , Chouinard Ghislain A , Mohn Robert , Duplisea Daniel E
Published: January 2006

Excessive and unsustainable fishing mortality was the predominant factor in the depletion of Northwest Atlantic cod (Gadus morhua) stocks. However, despite imposition of severe catch restrictions for over a decade, stocks have mostly failed to recover at predicted rates. A number of explanations have been considered. Our analysis of demographic characteristics of 12 of these stocks indicates that recent productivity over the northern portion of the range is much lower than 20 years previous when several stocks recovered from less severe declines. Main contributing factors are, in rank order, increased natural mortality, decreased body growth, and in a few cases, reduced recruitment rates. Continued fishing in directed and bycatch fisheries is also an important factor. Under current conditions, we estimate negative or very low (<2% per year) average growth rates in eight stocks. If fishing ceases, growth rates of >5% would be expected in six stocks, with >10% in four of these. Although productivity is low, we conclude that fishing mortality is further delaying recovery.
Ultra-high-energy cosmic rays from collisional annihilation revisited
Authors: Dick R , Hopp K M , Wunderle K E
Published: January 2006

We re-examine collisional annihilation of super-heavy dark-matter particles in dark-matter density spikes in the galactic halo as a possible source of ultra-high-energy cosmic rays. We estimate the possible flux in a way that does not depend on detailed assumptions about the density profiles of dark-matter clumps. The result confirms that collisional annihilation is compatible with annihilation cross sections below the unitarity bounds for super-heavy dark matter if the particles can form dense cores in the dark-matter substructure, and it provides estimates for core sizes and densities. The ensuing clumpy source distribution in the galactic halo will be tested within a few years of operation of the Pierre Auger observatory.PACS Nos.: 98.70.Sa, 98.70.f, 95.35.+d, 14.80.j
Laws of superposition of successive collinear Lorentz boosts
Authors: Antippa Adel F
Published: January 2006

We derive the laws of superposition of multiple successive collinear Lorentz boosts by four different methods. The first method exploits the relation between the Pochhammers of 2 x 2 nonautonomous matrices and the symmetric functions. The second method proceeds by diagonalizing the Lorentz boost. The third method is based on the characteristics of the Pauli matrices. The fourth method makes use of the relativistic law of addition of multiple collinear velocities, as well as the polygonometric identities. We give expressions, for the laws of superposition, parametrized using velocity and rapidity, as well as expressions in compact, symmetric, and unified forms. We also give the expressions of the laws of superposition in the special case of identical boosts, both for finite boosts, and for infinitesimal boosts. These latter results provide insight into the relation between Galilean (classical) and Lorentzian (relativistic) velocities.PACS Nos.: 03.30.+p, 02.10.Yn, 02.10.Ox
The effect of pore-water pressure on NATM tunnel linings in decomposed granite soil
Authors: Shin J H , Potts D M , Zdravkovic L
Published: January 2006

Tunnelling in a water bearing soil often produces a long-term interaction between the tunnel lining and the surrounding soil. With respect to lining design, infiltration and external pore-water pressures are often one of the most important factors to be considered. Development of pore-water pressure may accelerate leakage and cause deterioration of the lining. This can be particularly troublesome to structural and functional components of the tunnel and can often lead to structural failure. However, as a result of the complicated hydraulic boundary conditions and the long times often required for pore pressure equilibration, research on this subject is scarce. Consequently, most design approaches deal with the effects of pore-water pressure on the tunnel lining in a qualitative manner. In this paper, the development of pore-water pressure and its potential effects on the tunnel lining are investigated using the finite element method. In particular, the deterioration of a drainage system caused by clogging is considered. It is shown that the development of pore-water pressure on the lining is dependent on the lining permeability and the deterioration of the drainage system, particularly for a tunnel with both a primary and a secondary lining. The magnitude of pore-water pressure on a new Austrian tunnelling method (NATM) tunnel constructed in decomposed granite soil and the effect of tunnel shape are investigated. Design curves for estimating pore-water pressure loads on a secondary lining are proposed.Key words: numerical analysis, tunnel lining, decomposed granite.
Cyclic behaviour of a sand  steel plate interface
Authors: Oumarou Tahirou Assane , Evgin Erman
Published: January 2006

This paper presents the results of an experimental study on the mechanical behaviour of an interface between sand and a steel plate. A simple shear type interface apparatus is used. Tests are conducted under a two-way, displacement-controlled cyclic loading condition. The effects of the initial soil density, number of displacement cycles, magnitude of normal stress, and amplitude of tangential displacement on the cyclic response of the interface are investigated. The interface behaviour is presented in terms of the shear stress mobilized on the interface, the changes taking place in sample height, and the components of tangential displacements resulting from soil deformation and from slip between the soil and the steel plate during displacement cycles.Key words: cyclic behaviour, soilstructure interface, simple shear, slip, laboratory testing.
Formulation of a three dimensional analytical solution to evaluate stresses in backfilled vertical narrow openings
Authors: Li Li , Aubertin Michel , Belem Tikou
Published: January 2006

The mechanical response of backfill in narrow openings is significantly influenced by its interaction with the surrounding walls. Previous work conducted on backfilled trenches and mining stopes indicates that the theory of arching can be used to estimate earth pressures in narrow, vertical backfilled openings. In this paper, a 3D analytical solution is proposed to evaluate the state of stress along the boundaries of the openings. The proposed solution, based on a generalized version of the Marston approach, is compared with numerical modeling and laboratory experimental results taken from the literature. A discussion follows on some particular features and limitations of the analytical solutions.Key words: backfill, earth pressure, 3D openings, analytical solutions, trenches, mining stopes.
Modélisation numérique de l'apport du renforcement par boulonnage du front de taille des tunnels
Authors: Dias Daniel , Kastner Richard
Published: January 2006

We have first developed empirically the technique of reinforcement of the cutting face of tunnels, which allows for the excavation of full sections in layers of hardened soils or soft rock. Although numerous studies of numerical simulations have been proposed so far, the three-dimensional (3D) simulation of reinforcement of the cutting face of tunnels remains a heavy and costly procedure in terms of preparation and calculation, due in particular to the geometrical complexity and the different scale levels involved. Hence, it appears necessary to have at our disposal, especially at the pilot study stage, some simplified models that allow for a quick evaluation of the efficiency of the reinforcement. The bibliographical survey of the actual practices has led us to consider two methods: the first one consists of considering the effect of inclusions as equivalent to a pressure applied to the front, and the second one consists of a reinforcement of the cohesion ahead of the front along the length of the reinforcement. These two approaches have been compared to 3D calculations to evaluate their relevance.Key words: soil-structure interaction, tunnels, deformation, reinforced soils, numerical modelling, analysis.
Performance of engineered test covers on acid-generating waste rock at Whistle mine, Ontario
Authors: Adu-Wusu Celestina , Yanful Ernest K
Published: January 2006

This paper presents the design and 3 year field performance results of three engineered test soil covers for the mitigation of acid rock drainage (ARD) at Whistle mine near Capreol, Ontario. Each test cover was a two-layer system consisting of a 0.90 m noncompacted pit-run gravelly sand overlying a barrier layer. The three barrier layers studied were a 0.46 m thick mixture of sand (92%) and bentonite (8%) (SB), a 0.60 m thick layer of sandy silt with about 5% clay (SS), and a 0.008 m thick geosynthetic clay liner (GCL). Each cover was installed on 6.10 m thick acid-generating waste rock and was instrumented and monitored along with a control test plot that consisted of 6.10 m of waste rock. The ultimate objective of the study was to select a suitable cover for full-scale decommissioning of acid-generating waste rock backfilled into the Whistle pit. Results from 3 years of monitoring showed that the GCL was the most effective barrier in reducing percolation into the underlying waste rock. Percolation through the GCL barrier was 7% over the 3 year period compared with 20% and 59.6% through the sandbentonite and sandy silt barriers, respectively, and 56.4% through the control plot. The overall quality of percolate water from the covered waste rock was much better than that of percolate water from the uncovered waste rock. Aqueous geochemical modeling suggested that percolate water draining the oxidized waste rock was controlled by hydroxides, oxide, and sulphate phases of Al, Ca, Mg, and Fe3+.Key words: waste rock, acid rock drainage (ARD), capillary barrier, geosynthetic clay liner, amended soil systems, percolation, MINTEQ.
Distributions of ground movements parallel to deep excavations in clay
Authors: Roboski Jill , Finno Richard J
Published: January 2006

An empirical procedure for fitting a complementary error function (erfc) to settlement and lateral ground movement data in a direction parallel to an excavation support wall is proposed based on extensive optical survey data obtained around a 12.8 m deep excavation in Chicago. The maximum ground movement and the height and length of an excavation wall define the erfc fitting function. The erfc fit is shown to apply to three other excavation projects where substantial ground movement data were reported.Key words: excavations, clays, ground movements, performance data.
Kinetics of glycoluril template-directed Claisen condensations  Effect of thionation of the glycoluril
Authors: Kam Karen , Rahimizadeh Mohammad , McDonald Robert S , Harrison Paul HM , Chen Hao , Jenkins Stephen I , Pedrech Adrienne
Published: January 2006

Apparent rate constants for the tert-butoxide promoted Claisen-like condensation of a series of N1-acetyl-N6-aroyl-2,5-dithio-3,4,7,8-tetramethylglycolurils (9a9f) to give N1-(3′-aroyl-3′-oxopropionyl)-2,5-dithio-3,4,7,8-tetramethylglycolurils (10a10f) were determined by UV spectroscopy. Overall rate accelerations of 3.5- to 18-fold were found relative to the corresponding reactions of the 2,5-dioxo compounds (7a7f). Analysis of the Hammett plot for 9 and comparison with that for 7 shows that the key CC bond-forming step, where the enolate of the acetyl group of the substrate attacks the aroyl carbonyl group, is accelerated by the thio substitution. For electron-withdrawing substituents in the aroyl group, the acceleration is sufficient to make this step nonrate limiting: the Hammett ρ value drops from approx. 1.5 for electron-donating groups to 0.27 for electron-withdrawing groups. Deuterium substitution in the acetyl group reduces the rate slightly, a result consistent with a slow but partially reversible first step in which substrate is deprotonated. A similar acceleration and isotope effect are found when diacetyl glycoluril (2) and diacetyl dithio glycoluril (5) are compared. The implications of these results are discussed.Key words: glycoluril, Claisen condensation, kinetics, mechanism.
Photochemical generation and 1H NMR detection of alkyl allene oxides in solution
Authors: Breen Leah E , Schepp Norman P , Tan C-H Edmund
Published: January 2006

Irradiation of substituted 5-alkyl-4,5-epoxyvalerophenones leads to the formation of alkyl allene oxides that, in some cases, are sufficiently long-lived to be detected at room temperature by 1H NMR spectroscopy. Absolute lifetime measurements show that the size of the alkyl group has a significant influence on the reactivity of the allene oxide, with tert-butyl allene oxide having a lifetime of 24 h in CD3CN at room temperature that is considerably longer than the 1.5 h lifetime of the ethyl allene oxide. The allene oxides react rapidly with water to give α-hydroxyketones. The mechanism involves nucleophilic attack to the epoxide carbon to give an enol, which can also be detected as an intermediate by 1H NMR spectroscopy.Key words: allene oxides, mechanisms, absolute reactivity, kinetics, photochemistry.
Kinetic isotope effect evidence for the concerted transfer of hydride and proton from hydroxycyclopentadienyl ruthenium hydride in solvents of different polarities and hydrogen bonding ability
Authors: Casey Charles P , Johnson Jeffrey B
Published: January 2006

The tolyl analogue of Shvo's hydroxycyclopentadienyl ruthenium hydride (4) efficiently transfers a hydride and proton to benzaldehyde or acetophenone to produce an alcohol. This reduction can be performed in toluene, methylene chloride, and THF. Reduction of benzaldehyde in toluene and methylene chloride occurs approximately 300 times faster than in THF at 0 °C. Reduction of acetophenone occurs between 75 and 150 times slower than benzaldehyde at 0 °C in each respective solvent. Despite the differences in rate, mechanistic studies have provided evidence for a similar concerted transfer of acidic and hydridic hydrogens in each solvent. Addition of water to THF led to further rate decrease coupled with an increase in the OH/D kinetic isotope effect and a decrease in the RuH/D kinetic isotope effect. Addition of excess alcohol to toluene or methylene chloride results in the significant retardation of the rate of reduction. The slower rate in THF and in the presence of alcohol is attributed to the stabilization of the ground state of ruthenium hydride 4 by hydrogen bonding and the additional energy required to break these bonds prior to carbonyl reduction.Key words: ruthenium hydrogenation catalysis, hydrogenation mechanism, kinetic isotope effects, ligandmetal bifunctional catalysis.
Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph2Ge:) precursors
Authors: Harrington Cameron R , Leigh William J , Chan Bryan K , Gaspar Peter P , Zhou Dong
Published: January 2006

The photochemistry of diphenylbis(trimethylsilyl)germane (2a) and 1,4-dihydro-5-methyl-1,2,3,4,9,9-hexaphenyl-1,4-germanonaphthalene (11) has been studied in solution by steady-state and laser flash photolysis methods with a view to detecting the transient germylene derivative diphenylgermylene (Ph2Ge), which has previously been shown to be the major product of photolysis of 2a and a closely related derivative of 11. Steady-state trapping experiments confirm the formation of Ph2Ge as the major germanium containing primary product in both cases; with 2a, the results indicate that other transient species are also formed in minor yields, including phenyl(trimethylsilyl)germylene (Ph(TMS)Ge, ca. 6%) and diphenyl(trimethylsilyl)germyl radicals (Ph2(TMS)Ge, ≥15%). Laser flash photolysis of 2a in deoxy genated hexane solution yields a complex mixture of overlapping transient absorptions, which is shown to be comprised of Ph2Ge, tetraphenyldigermene (15) and its oligomerization products, and another species with spectral characteristics similar to the Ph2(TMS)Ge radical. The latter has been independently generated by hydrogen abstraction from diphenyl(trimethylsilyl)germane by tert-butoxyl radicals. Compound 11 extrudes Ph2Ge more cleanly and efficiently upon photolysis in solution, yet laser flash photolysis affords excited triplet and triplet-derived species as the only detectable transient products; interpretation of the results for this compound is made difficult by its slow thermal decomposition to 5-methyl-1,2,3,4-tetraphenylnaphthalene. It is concluded that in spite of the fact that both 2a and 11 afford Ph2Ge in high yield upon photolysis, they are poor precursors for study of the species in solution by time-resolved UVvis methods, owing to the formation of other, more strongly absorbing transient products than Ph2Ge, whose lowest energy absorption is characteristically weak.Key words: germylene, germyl radical, flash photolysis, disilylgermane, photochemistry.
The role of molecular geometry in the Wolff rearrangement of α-diazocarbonyl compounds  Conformational control or structural constraints?
Authors: Popik Vladimir V
Published: January 2006

Relaxed scans of potential energy surfaces for the loss of nitrogen from four different diazocarbonyl compounds: 3-diazo-2-butanone (1), 2-diazocyclohexanone (2), methyl diazomalonate (3), and diazo Meldrum's acid (4), were conducted at the B3LYP/6-31+G(d,p) level. The geometries of species and transition states involved in the process were optimized at the B3LYP/6-311+G(3df,2p) level, while electronic energies were computed using the MP2(full)/aug-cc-pVTZ method. These calculations suggest that the rigidity of cyclic molecules, rather than the conformational structure of the starting diazocarbonyl compounds, defines the pathway of the dediazotization reaction. In acyclic diazocarbonyl compounds, loss of nitrogen results in the formation of a carbene, which is stabilized by the overlap of the system of carbonyl group and the unshared electron pair of a singlet carbene. On the contrary, in small- to medium-sized cyclic systems, carbonyl carbenes are unable to attain a stabilizing orthogonal conformation. Consequently, cyclic carbonyl carbenes are less stable, and the concerted Wolff rearrangement becomes the predominant process. Transition states for the concerted Wolff rearrangement and for the formation of carbonyl carbenes have a very similar geometry.Key words: diazocarbonyl compounds, Wolff rearrangement, conformation, carbene, ketene.
Scientific genealogies of physical and mechanistic organic chemists
Authors: Andraos John
Published: January 2006

Scientific genealogy trees of scientists who contributed to the study of organic reaction mechanisms over the last century are presented. The trees show doctoral and post-doctoral connections among scientists as well as connections between scientific ideas. Contributions made by scientists working in laboratories at Canadian universities and at the National Research Council of Canada are noted throughout. These trees, covering more than two centuries, are of interest to senior scientists and young students of science alike in understanding the evolution of scientific ideas and in career development for aspiring scientists. Key patterns revealed by these trees pertaining to ideas and discoveries made, how they were made, connections between them, and who made them are also discussed.Key words: reaction mechanisms, physical organic chemistry, scientific genealogies.
Elimination reactions  Calculation of rate constants from equilibrium constants and distortion energies by means of no barrier theory
Authors: Guthrie J Peter , Leandro Leonardo , Pitchko Vladimir
Published: January 2006

No barrier theory has been applied to the E2 reactions of five alkyl bromides with ethanolic ethoxide. The model used for these reactions is that the reaction proceeds from the encounter complex of base and alkyl halide to the product encounter complex of halide ion and alkene (and alcohol), and requires five simple processes, which combine to give the concerted elimination: transfer of a proton from carbon to base; a change in geometry at the carbon which loses a proton from sp3 to sp2; breaking the C-leaving group bond; a change in geometry at the carbon which loses the leaving group from sp3 to sp2; and a change in the length of the carboncarbon bond. The free energy of activation can be calculated with an rms error of 2.58 kcal mol1 (1 cal = 4.184 J).Key words: Elimination, no barrier theory, rate constant, equilibrium constant.
Valence bond calculations on the transition state for the E2 reaction of fluoride ion with ethyl fluoride  Implications for the More O'Ferrall  Jencks diagram
Authors: Wu Wei , Shaik Sason , Saunders, Jr. William H
Published: January 2006

A valence bond self-consistent field (VBSCF) calculation has been carried out on the bimolecular elimination (E2) reaction of fluoride ion with ethyl fluoride. The transition state was first optimized at HF/6-31+G and the resulting orbitals were used in the VBSCF calculation. A transition-state hybrid consisting of four structures (FH-CH2-CH2-F, F-HCH2=CH2F, F-HCH2-CH2-F, and FH-CH2-CH2+F) failed to give a reasonable energy. Incorporation of four charge-separated structures (FH+CH2-CH2-F, FH+CH2-CH2+F, FH+CH2=CH2F, and F-HCH2-CH2+F) for a total of eight resulted in an energy slightly below HartreeFock. A full-space VBSCF calculation utilizing 50 structures showed that the eight structures give a sufficiently accurate wave function. The transition state is dominated by charge-separated structures, leading to a greater degree of charge separation than in either the reactant or product complex. Therefore, the transition state does not evolve synchronously from the reactants, and explicit allowance should be made for this fact when applying descriptions of the reaction path, such as that in the More O'Ferrall  Jencks diagram. Key words: elimination reaction, E2, transition state, VBSCF calculation, XMVB programs.