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Surrounding Water (surrounding + water)
Selected AbstractsSeismic response of intake towers including dam,tower interactionEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2009M. A. Millán Abstract The seismic response of the intake,outlet towers has been widely analyzed in recent years. The usual models consider the hydrodynamic effects produced by the surrounding water and the interior water, characterizing the dynamic response of the tower,water,foundation,soil system. As a result of these works, simplified added mass models have been developed. However, in all previous models, the surrounding water is assumed to be of uniform depth and to have infinite extension. Consequently, the considered added mass is associated with only the pressures created by the displacements of the tower itself. For a real system, the intake tower is usually located in proximity to the dam and the dam pressures may influence the equivalent added mass. The objective of this paper is to investigate how the response of the tower is affected by the presence of the dam. A coupled three-dimensional boundary element-finite element model in the frequency domain is employed to analyze the tower,dam,reservoir interaction problem. In all cases, the system response is assumed to be linear, and the effect of the internal fluid and the soil,structure interaction effects are not considered. The results suggest that unexpected resonance amplifications can occur due to changes in the added mass for the tower as a result of the tower,dam,reservoir interaction. Copyright © 2008 John Wiley & Sons, Ltd. [source] Undulatory fish swimming: from muscles to flowFISH AND FISHERIES, Issue 2 2006Ulrike K. Müller Abstract Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle-fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle-fibre types are better served by non-uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone-shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone-shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water , the wake of carangiform swimmers shows a net backward momentum without the fish accelerating , suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings. [source] Functionalization of PAMAM dendrimers with nitronyl nitroxide radicals as models for the outer-sphere relaxation in dentritic potential MRI contrast agentsMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2003Giancarlo Francese Abstract PAMAM dendrimers functionalized with nitronyl nitroxide radicals were characterized. Quantitative determination of substitution with radicals was performed using EPR and electrochemical methods. The study of the 1H NMR relaxation of the surrounding water showed how the outer-sphere contribution to the relaxivity may be limited by the presence of the dendrimer core. Copyright © 2003 John Wiley & Sons, Ltd. [source] Transitions in function at low Reynolds number: hair-bearing animal appendagesMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 17-18 2001M. A. R. Koehl Abstract Many types of animals use appendages bearing arrays of hair-like structures to capture molecules (e.g. olfactory antennae, gills) or particles (e.g. suspension-feeding appendages) from the surrounding water or air, and to locomote or move fluid past themselves. The performance of these functions depends on how much of the fluid encountered by the array of hairs flows through the gaps between the hairs rather than around the perimeter of the whole array. By modelling such arrays of hairs as rows of finite width of cylinders operating at low Reynolds numbers, the fluid velocity fields with respect to the hairs were calculated. Such models revealed a transition from non-leaky to leaky behaviour as Re was increased. The purpose of this paper is to provide a brief review of the features of this transition as revealed by models, and then to describe examples of how animals use the transition in fluid flow to perform particular functions: rejection of captured material by copepods, and sniffing by lobsters. Copyright © 2001 John Wiley & Sons, Ltd. [source] Measuring SPIO and Gd contrast agent magnetization using 3,T MRINMR IN BIOMEDICINE, Issue 8 2009Pádraig Cantillon-Murphy Abstract Traditional methods of measuring magnetization in magnetic fluid samples, such as vibrating sample magnetometry (VSM), are typically limited to maximum field strengths of about 1,T. This work demonstrates the ability of MRI to measure the magnetization associated with two commercial MRI contrast agents at 3,T by comparing analytical solutions to experimental imaging results for the field pattern associated with agents in cylindrical vials. The results of the VSM and fitted MRI data match closely. The method represents an improvement over VSM measurements since results are attainable at imaging field strengths. The agents investigated are Feridex, a superparamagnetic iron oxide suspension used primarily for liver imaging, and Magnevist, a paramagnetic, gadolinium-based compound used for tumors, inflammation and vascular lesions. MR imaging of the agents took place in sealed cylindrical vials in the presence of a surrounding volume of deionized water where the effects of the contrast agents had a measurable effect on the water's magnetization in the vicinity of the compartment of contrast agent. A pair of phase images were used to reconstruct a B0 fieldmap. The resultant B0 maps in the water region, corrected for shimming and container edge effects, were used to predict the agent's magnetization at 3,T. The results were compared with the results from VSM measurements up to 1.2,T and close correlation was observed. The technique should be of interest to those seeking quantification of the magnetization associated with magnetic suspensions beyond the traditional scope of VSM. The magnetization needs to be sufficiently strong (Ms , 50 Am2/kg Fe for Feridex and Xm , 5 × 10,5 m3/kg Gd for Magnevist) for a measurable dipole field in the surrounding water. For this reason, the technique is mostly suitable for undiluted agents. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison of ion transportation before and after egg hatching in Amphinemura sp. (Plecoptera)PHYSIOLOGICAL ENTOMOLOGY, Issue 4 2006MAYUMI YOSHIMURA Abstract An increase in egg size with embryonic development in stoneflies is believed to result from the uptake of water by osmosis. The present study aims to investigate whether a selective ion transport through egg membranes exists before hatching, and whether ions are released after hatching. Viable and nonviable egg masses are incubated in Petri dishes filled with water, and the concentrations of the ions F,, Cl,, SO42,, NO3,, Na+, K,, Mg2+ and Ca2+ in the water are determined. The ion transport of an egg mass before and after hatching and a nonviable egg mass is then calculated. Before hatching, Cl,, SO42,, NO3,, Na+, Mg2+ and Ca2+ are taken up from the surrounding water into the inner egg. These ions are selectively taken into the egg. After hatching, Cl,, SO42,, Na+, Mg2+ and Ca2+ are released into the surrounding water. The amount of these ions released after hatching is lower than the amount taken up before hatching. Ions that are not released after hatching are considered to be used in embryonic development. [source] Relation between metal concentration in water and metal content of marine mussels (Mytilus galloprovincialis): Impact of physiology,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2008Stellio Casas Abstract The present study constitutes an in situ investigation of metal kinetics within soft tissue of mussels (Mytilus gallo-provincialis), which solves the problem of the decoupling of the effect of animal physiology and metal bioavailability in water. Field experiments were conducted to measure uptake and elimination kinetics for four metals (Hg, Pb, Cd, and Cu) in three Mediterranean sites with different contamination and nutritive levels. At each site, metal concentrations were monitored in soft tissues of mussels and in the surrounding waters. The experimental conditions were completely characterized: Lazaret Bay (located between Nice and Marseille, France) is a hot spot for Hg (6.3 ng/L) and Pb (163 ng/L) concentrations and is an oligotrophic, stable site; Bages Lagoon (located to the west of Montpellier, France) is particularly contaminated by Cd (1.5 ng/L) and Cu (1.5,g/L) and is a mesotrophic site where variability of trophic and physicochemical parameters is significant; and Port-Cros Island (located in the Hyeres National Park, France) is considered to be a reference site. Those kinetics permit us to decouple physiological, chemical, and environmental interactions. After normalizing mussel metal content for similar physiological conditions, application of the local weighted regression (LOWESS) statistical treatment shows a parallelism between the time trends of metal concentrations in the bivalve and metal concentrations in water. The results enabled us to obtain in situ kinetic parameters and realistic bioaccumulation factors. Their logarithmic values were 4.6 for Hg, 4.3 for Pb, 4.9 for Cd, and 3.9 for Cu. The importance of physiological processes such as spawning is discussed as a factor influencing the bioaccumulation factor. This information may be useful in refining monitoring tools for risk assessment and, more generally, in environmental management strategies. [source] Advection of anchovy (Engraulis encrasicolus) larvae along the Catalan continental slope (NW Mediterranean)FISHERIES OCEANOGRAPHY, Issue 2 2007A. SABATÉS Abstract The Gulf of Lions is one of the main anchovy (Engraulis encrasicolus) spawning areas in the NW Mediterranean. During the spring, low-salinity surface water from the outflow of the Rhône is advected by the shelf-slope current along the continental slope off the Catalan coast. In June 2000, a Lagrangian experiment tracking these low-salinity surface waters was conducted to assess the importance of this transport mechanism for anchovy larvae and to determine the suitability of the tracked surface waters for survival of anchovy larvae. The experiment consisted of sampling the tracked water parcel for 10 days with three drifters launched at the core of the shelf-slope current where low-salinity surface waters were detected. The survey was completed by sampling the surrounding waters. Anchovy larvae from the spawning area in the Gulf of Lions were advected towards the south in the low-salinity waters. The size increase of anchovy larvae throughout the Lagrangian tracking closely followed the general growth rate calculated by otolith analysis (0.65 mm day,1). However, advection by the current was not the only mechanism of anchovy larval transport. A series of anticyclonic eddies, originated in the Gulf of Lions and advected southwards, seemed to play a complementary role in the transport of larvae from the spawning ground towards the nursery areas. These eddies not only contributed to larval transport but also prevented their dispersion. These transport and aggregation mechanisms may be important for anchovy populations along the Catalan coast and require further study. [source] DETECTION OF SALMONELLA TYPHIMURIUM IN OYSTERS BY PCR AND MOLECULAR HYBRIDIZATIONJOURNAL OF FOOD QUALITY, Issue 5 2006A.A. CORRĘA ABSTRACT Because shellfish (oysters, clams and mussels) are filter feeders, i.e., able to concentrate pathogens from the surrounding waters within their tissues, they have been widely associated with outbreaks illness. The incidence of salmonellosis caused by the consumption of raw or undercooked shellfish, is a primary concern of public health agencies. Then, in recent years, more rapid and specific methods based on the DNA sequence of salmonella genes have been developed to detect low levels of pathogens in environmental and food samples. In this study, we developed a sensitive method to detect low levels of Salmonella typhimurium in oyster tissues (0.1 cfu/g). This methodology consisted of dissection of the gastrointestinal oyster tract, pre-enrichment of the samples in nonselective medium, DNA extraction and polymerase chain reaction followed by molecular hybridization using a digoxygenin-labeled amplicon-derived probe. These results can benefit the public health agencies and shellfish producers concerning microbiological and quality aspects of the commercial oyster production. [source] | ||||||||||||||||