bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Reinforcement of Three-Dimensional Spacer Fabric Composites
Authors: Wang Shao Kai , Li Min , Gu Yi Zhuo , Zhang Zuo Guang , Wu Bo Ming
Published: June 2010

Three-dimensional (3-D) spacer fabric composite is a novel lightweight sandwich structure, the reinforcement of which is integrally woven with two facesheets connected by continuous fibers (named piles) in the core. Usually the 3-D spacer fabric composite without extra reinforcement is called mono-spacer fabric composite, which provides outstanding facesheet / core debonding resistance. However, its mechanical properties cannot meet the demand of structure application because of the thin facesheet and low load-bearing capacity of high piles. Hence, two reinforcement methods were developed by laminating additional weaves at the facesheet and filling foam materials in the core to strengthen the facesheet and piles, respectively. This paper aims to investigate the influences of reinforcement methods on the mechanical behaviors and damage modes of 3-D spacer fabric composites under flatwise compressive, shear, edgewise compressive and three-point bending loads, by comparing with mono-spacer fabric composites. The results indicate that additional weaves reinforcement can enhance edgewise compressive and flexural properties effectively. Foam filling is one of the best options to improve the flatwise compressive and shear properties, and especially, there are synergistic effects between piles and foam under flatwise compressive load. Besides, the failure modes of reinforced and mono-spacer fabric composites are different.
Hot-Working Behaviour of Advanced High-Manganese C-Mn-Si-Al Steels
Authors: Dobrzański Leszek Adam , Borek Wojciech
Published: June 2010

The high-manganese austenitic steels are an answer for new demands of automotive industry concerning the safety of passengers by the use of materials absorbing high values of energy during collisions. The chemical compositions of two high-manganese austenitic steels containing various Al and Si concentrations were developed. Additionally, the steels were microalloyed by Nb and Ti in order to control the grain growth under hot-working conditions. The influence
of hot-working conditions on a recrystallization behaviour was investigated. Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages
of deformation was determined in metallographic investigations using light microscopy. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. Making use of dynamic and metadynamic recrystallization,
it is possible to refine the microstructure and to decrease the flow stress during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. The obtained microstructure – hot-working relationships can be useful in the determination of powerful parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures.
Fabrication and Properties of a Combined Structural Cu Sheet for Interconnect Material
Authors: Shin Je Sik , Moon Hyung Kwon , Kim Bong Hwan , Lee Hyo Soo , Kwon Hyouk Chon
Published: June 2010

In this study, it was aimed to develop a novel interconnect material simultaneously possessing high electrical conductivity and strength. Combined structural Cu sheets were fabricated by forming the high electrical conduction paths of Ag on the surface of high strength Cu alloy substrate by damascene electroplating. As a result, the electrical conductivity increased by 40%, while the ultimate tensile strength decreased by only 20%. When the depth of Ag conduction path was deep, fracture zone ratio as well as roll-over zone increased.
Superior Radiation Resistance of ODS Ferritic Steels
Authors: Kasada Ryuta , Takahashi Hiromasa , Kishimoto Hirotatsu , Yutani Kentaro , Kimura Akihiko
Published: June 2010

The oxide dispersion strengthened (ODS) ferritic steel and non-ODS reduced-activation ferritic (RAF) steel were irradiated at 773 K by means of a dual-beam ion irradiation technique to a dose of 0.4 dpa with simultaneous helium implantation up to 1000 appm. Microstructural changes were investigated by transmission electron microscopy. The RAF steel showed a preferential formation of cavities at grain boundaries, precipitate interfaces and dislocations. In contrast, the ODS ferritic steel showed a homogeneous and fine distribution of cavities in the matrix. This paper discusses the superior resistance of the ODS ferritic steel against development of cavities in terms of the effects of nano-oxide particles dispersed in the matrix.
Development of High Power Density Solid Oxide Fuel Cells (SOFCs) for Long-Term Operation
Authors: Menzler Norbert H. , Schafbauer Wolfgang , Han Feng , Büchler Oliver , Mücke Robert , Buchkremer Hans Peter , Stöver Detlev
Published: June 2010

Solid oxide fuel cells (SOFCs) enable environmentally friendly energy to be produced with high efficiency. The market entry of SOFC systems depends on the functionality of the components and on the costs. The SOFC has not yet reached market maturity. This presentation focuses on the possibilities for manufacturing SOFCs with high power outputs and long-term durability by using manufacturing technologies feasible in industry. For the past 15 years, FZ Jülich has been developing large-size so-called anode-supported SOFCs (up to 200 x 200 mm²) with reproducibly high power output (> 2 A/cm² at 800°C). Novel technologies for high-capacity manufacturing such as tape casting and roller coating have been introduced. Additionally, newly developed thin-film techniques have led to power outputs of more than 3 A/cm² at 800°C and more than 1.5 A/cm² below 700°C. These high power densities open up new possibilities for the operation of SOFCs at low temperatures to ensure low degradation and therefore long lifetimes.
Welding Technology of Ultra-Low Carbon and Nitrogen Ferrite Stainless Steel
Authors: Wang Bao Sen , Zhu Shuang Chun , Ye Xia Ning
Published: June 2010

Weldability of ultra low carbon and nitrogen, low chromium ferrite stainless steel is analysed by using Thermol-cal software and welding metallurgy. Eembrittlement of welding joint is the failure reason during application of ultra low carbon and nitrogen 12% chromium FSS. Comparing welding joint performance of different welding process, Gas Metal Arc Weldinng with high toughness welding material and proper welding heat input is economical and feasible welding process. Controlling growth of ferrite grain is the key to improve toughness of the heat affected zone (HAZ). Presence of titanium carbides or nitrides and the amount of martensite located along ferrite grain intergranular boundaties are very important for toughness of HAZ in low chromium FSS. It was found that the best size of Ti(C/N) grain is 2-5μm and content of martensite is 40%.
Microstructure and Mechanical Properties of Al Added Ni3(Si,Ti) Intermetallic Thin Sheets
Authors: Kaneno Yasuyuki , Fujimoto Yasunori , Takasugi Takayuki
Published: June 2010

The effect of Al addition on microstructures and tensile properties of cold-rolled Ni3(Si,Ti) intermetallic alloys with L12 ordered structure, which were fabricated through thermomechanical processing from arc-melted ingots, were investigated. Addition of 4 and 8 at.% Al to Ni3(Si,Ti) was conducted in two ways that Al substituted for Ti site and both for Ni and Ti sites, respectively. The alloys made by the former way showed a two-phase microstructure consisting of disordered fcc Ni solid solution dispersions in the L12 matrix, irrespective of Al contents, while the 4 at.% Al alloy made by the latter way exhibited an L12 single-phase microstructure. These alloys were successfully cold-rolled to thin sheets with a thickness of 200 μm except the 8 at.% Al alloy made by the latter way. For the thermomechanically processed 4 at.% Al alloys, high-temperature yield stress was higher in the alloy made by the latter way than in the alloy made by the former one, suggesting that the single-phase microstructure consisting of whole L12 ordered structure is favorable for high-temperature tensile property.
Isothermal Oxidation Behavior of a New Directionally Solidified Ni-Base Superalloy in Air at Different Temperature
Authors: Wang Lei , Huang Yan , Zhao Zhuo , Liu Yang , Wu Jian Tao , Yan Ping
Published: June 2010

The isothermal oxidation behaviour under static atmosphere of a new directionally solidified Ni-base superalloy was investigated. The results showed that the oxidation kinetics curves of the alloy follow parabolic law in the temperature range of 750-950°C. The diffusion activation energy Q is to be about 244.86 kJ•mol-1 and the oxidation within this temperature range is mainly controlled by Cr3+ diffusion among Cr2O3 oxidation film. The oxidation resistance grade of the alloy is perfect anti-oxidation within 750-850°C, and anti-oxidation within 900-950°C. The oxidation film can be divided into TiO2, Cr2O3+TiTaO4+NiCr2O4, Al2O3 and TiN layers, from the surface to inside. Priority oxidation and the inside oxidation of Al are considered with the oxidation of Ti and the depletion of Cr, and it is the key point for the improving of oxidation resistance.
High-Temperature Sulfurization of Crofer 22APU in H2/H2S Atmosphere
Authors: Żurek Zbigniew , Jaron Artur , Stawiarski Adam , Gil Aleksander
Published: June 2010

The authors present studies of behavior of Crofer steel in H2 polluted by H2S. The high temperature corrosion behavior of Crofer 22APU steel pre-oxidized samples and not pre-oxidized ones were studied in the temperature range of 600 – 900°C in H2/H2S atmospheres in sulphur vapor pressures in the range of 10-7-10-1 Pa. Kinetics depend on the temperature and sulphur pressure, however the process of sulfurization for pre-oxidized samples was slower.
The Influence of Eutectic Morphology on the Impact Properties of High Pressure Die Cast Mg-Rare-Earth Alloys
Authors: Easton Mark , Strobel Katharina , Zhu Su Ming , Gibson Mark A. , Nie Jian Feng
Published: June 2010

The impact properties of high-pressure die cast Mg-RE alloys were investigated. It was found that, for rare earth contents between 2-4 wt.%, the Mg-La and Mg-Nd alloys performed better than the Mg-Ce alloys in un-notched tests. The notched results appear to be related to the amount of intermetallic. In contrast, the un-notched results indicate that at some compositions the Mg-La alloys out-performed the other alloys when compared to the amount of intermetallic. It was apparent that a lamellar eutectic structure can improve the un-notched impact properties of Mg-RE based alloys even when this is not evidenced in tensile test or notched impact results.
Topology of Spheroidized Pearlite
Authors: Adachi Yoshitaka , Wang Yuan Tsung
Published: June 2010

Differential geometry and toplogy-based three-dimensional (3D) analysis was conducted to understand pearlite spheroidization mechanism in an eutectoid steel. Morphological change during aging below A1 tempearture was examined in terms of Gaussian(K)/mean curvatures(H), genus and Euler characteristics based on 3D images.The holes presentnaturally grown cementite lamella caused shape instability andinduced shape evolution of the lamellar structure during spheroidization. 3D visualization demonstrated that the intrinsic holes played an important role in the initiation and development of pearlitespheroidization. The hole coalescence and expansion causedthe breakup of large cementite lamellae into several long narrow ribbons. H-K plot actually suggested that the number of thses holes decreased with increasing aging period. In addition, small cementite particles and narrow rod cementite decreased during aging. These microstractural evolutions were discussed from the view point of ferrite/cementite interfacial energy.
Microstructural Evolution during Friction Stir Processing of Magnesium Alloy Castings
Authors: Robson Joseph D. , Cui Song , Chen Zhanwen
Published: June 2010

Friction stir processing (FSP) of cast AM60 magnesium alloy has been studied using the breaking pin method, freezing the microstructure during the process. Strong evidence is seen that partial melting plays a key role in removing the β-Mg17Al12, whereas the manganese rich intermetallics persist during FSP. This is consistent with temperature predictions made using a process model adapted to FSP of AM60 castings that show the eutectic melting point is exceeded.
Modelling the High Temperature Deformation of Ti-6Al-4V
Authors: Zhong Ji Kang , Dargusch Matthew S. , Davies Chris H.J.
Published: June 2010

The hot deformation behaviour of the alpha / beta Ti-6Al-4V alloy was investigated at various temperatures and strain rates by means of compression and torsion tests. As expected, the peak flow stress increased with increasing strain rate and decreased as the initial sample temperature was increased. The different flow behaviours observed are discussed in terms of the volume fraction of each phase. The dual phase Ti-6Al-4V alloy was assumed to be a composite material containing a soft phase and a hard phase. By taking into consideration the phase-to-phase interaction and volume fraction change with temperature, constitutive models are proposed to simulate the deformation behaviours. By application of the rule of mixtures the modelled yield stresses showed good agreement with the experiment results.
Characterization of Microstructure and Mechanical Properties of a Nb-Microalloyed Steel after Quenching-Partitioning-Tempering Process
Authors: Wang Xiao Dong , Guo Zheng Hong , Rong Yong Hua
Published: June 2010

A novel heat treatment process, that is, quenching-partitioning-tempering (Q-P-T) process, has been developed as a new way to obtain ultrahigh strength martensitic structural steel containing retained austenite and alloying carbide. In order to display merit of the Q-P-T process, a medium carbon Nb-microalloyed steel is treated by Q-P-T 1-step process and Q-P-T 2-step process, as well as treated by the transformation induced plasticity heat treatment process and quenching and tempering process, respectively. The results show that Q-P-T samples possess better mechanical properties than those treated by other heat treatment processes. The origin of the good mechanical properties is analyzed based on the phase and microstructure characterization using X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
Joint Interface Morphology of Friction Stir Spot Welded Aluminum Alloy Sheets and Plated Steel Sheets
Authors: Feng Keyan , Watanabe Mitsuhiro , Kumai Shinji
Published: June 2010

Friction stir spot welding (FSSW) was applied to lap joining of aluminum alloy sheets and steel sheets. A 1.2 mm-thick non-plated carbon steel sheet and plated steel sheets with zinc alloy (ZAM), pure zinc (GI), zinc alloy including Fe (GA) and Al-Si alloy (AS) were prepared. The melting temperature of the plated layer is 330, 420, 880 and 640°C, respectively. A 1.1 mm-thick 6022 aluminum alloy sheet was overlapped on the steel sheet. A rotating tool was inserted from the aluminum alloy sheet side and the probe tip was kept at the position of 0.2 mm above the lapped interface for 3 seconds. For ZAM and GI, original plated layers were removed from the interface and intermediate layers were formed at the joint interface. This is because the melting temperature of the plated layer was lower than the interface temperature under the rotating probe tip during the FSSW. In contrast to that, the partial original plated layer remained after welding, and additional layer formed at the plated layer /aluminum alloy interface for GA. For AS, Al-Fe intermetallic compound layer, which was formed at the original Al-Si alloy plated steel surface remained.
Port-Based Modeling of Distributed-Lumped Parameter Systems
Authors: Orlikowski Cezary , Hein Rafał
Published: June 2010

This paper presents a uniform, port-based approach for modeling of both lumped and distributed parameter systems. Port-based model of the distributed system has been defined by application of bond graph methodology and distributed transfer function method (DTFM). The proposed approach combines versatility of port-based modeling and accuracy of distributed transfer function method. A concise representation of lumped-distributed systems has been obtained. The proposed method of modeling enables to formulate input data for computer analysis by application of DTFM.
Parametrization of all Three Impulse Zero Vibration Input Shapers
Authors: Schlegel Miloš , Bláha Lukáš
Published: June 2010

Input shaping has been demonstrated to be a simple method of reducing vibration in many types of controlled machines. The method is implemented by convolving a command signal with an impulse sequence of input shaper to produce a shaped input that is then used to command the system. Designing the input shaper involves determining the amplitudes and timing of the impulses such that the resulting shaped commands lead to desired levels of vibration reduction. Up to now, to the best knowledge of the authors, it is known only few special types of input shapers (ZV, ZVD, ZVDk, EI, SI,...). This paper presents two general approaches for parametrization of all three impulse zero vibration input shapers.
Movement Trajectory Planning Algorithm of Rotating Mobile Piezorobot
Authors: Bansevičius Ramutis , Drukteiniene Asta , Kulvietis Genadijus
Published: June 2010

his paper presents method for trajectory planning of mobile piezorobots. An algorithm for evaluation of motion trajectory for this kind of robots, describing point-to-point motion by means of the given function is presented. Preliminary experimental results prove the feasibility of proposed mathematical model.
Mechatronic System for Automatic Inspection of Circular Saw Teeth
Authors: Kapcia Jerzy , Orlowski Kazimierz A. , Wasielewski Roman
Published: June 2010

The paper presents a mechatronic system for automatic inspection of circular saw teeth. The described system, based on numerical processing of recorded tooth images, has been implemented in the automatic vision controller system WKOPTar. The applied mechatronic system for the automatic spindle control positioning guarantees for the circular saw blade teeth a proper position enabling to grab and record tooth images even for non-uniform pitches in the examined circular saw blade. Some examples of measurements and geometry analyses of circular saw teeth were provided in order to illustrate the diagnostic usability of the apparatus. The system allows the user to determine up to 32 parameters for one tooth. However, the direct interpretation of physical parameter is sometimes partially limited by the software because the same parameter might have different meaning. Thus, in some cases a proper interpretation of the results may be feasible after recorded tooth screen analyses.
Development of a Novel Micro-Actuator Driven by Shape Memory Alloy
Authors: Pan Chi Hsiang , Wang Ying Bin
Published: June 2010

This paper presents a novel microactuator driven by shape memory alloy (SMA). First, the helical spring-shaped SMA is fabricated from SMA wire (Ti50%-Ni45%-Cu5%) with one way shape memory effect and 0.6 mm in diameter. Subsequently, a compliant tube-type microactuator driven by helical spring-shaped SMA is developed. The performances of the helical spring-shaped SMA and the compliant tube-type microactuator, such as the response time, the recovery force and the surface temperature in terms of the driving currents, are investigated. The driving circuit system comprising a pulse width modulation (PWM) control circuit is used to drive the actuator. Experiments demonstrate that control of the SMA actuator using PWM effectively reduces the energy consumption and ensures a short cooling time to guarantee a high response time in actuating cycles. Finite element software (COSMOSWorks) is applied for the analysis of the compliant tube-type actuator, which aim is to demonstrate the agreement between the theoretical analysis and experiment as well as to improve the performance of the actuators.
High Temperature Corrosion of Evaporator Tubes with Thermal Sprayed Coatings
Authors: Łabanowski Jerzy , Ćwiek J.
Published: June 2010

Degradation examinations of outer surface of low-emission steam boiler evaporator tubes are presented in the paper. Metallographic evaluation of scale morphology as well as determination of chemical composition of micro sites and distribution of elements on cross-sections is reported. Water-wall tubes were exposed in steam boiler for up to two years period. Common tubes produced from 16Mo3 steel suffered sulphide and molten salts corrosions. Thermal sprayed tubes with the single layer of 70%Ni 30%Cr alloy demonstrate better corrosion resistance, but become susceptible to sulphide corrosion due to presence of internal voids and cracks. Double layer Al2O3/Ni-30Cr coatings withstood corrosion attack for more than one year of operation, and then failed due to internal heterogeneity and crack generation.
The Influence of Plastic Strain on the Corrosive Properties of Plasma Sprayed Intermetallic NiAl and Ni3Al Coatings
Authors: Starosta Robert
Published: June 2010

The paper presents the preliminary research results that were aimed at working out a technology of the surface roughness reduction by means of plastic working methods. The intermetallic phase NiAl and Ni3Al coatings that were plasma sprayed on a flat bar made of non-alloy steel (C45) were chosen for the research. The coatings underwent plastic working with the use of press. Three specific loads were used: 500, 800, 1100 MPa. The treated coatings exhibited 70% lower surface roughness as compared to thermally sprayed layers. However, high values of relative strain of coatings ( = 0.21 – 0.62) were obtained. Plastic working resulted in the decrease of corrosive potential values and increase of corrosive current density.
Determination of Centre of Gravity of Machines with the Rail Undercarriage
Authors: Smolnicki Tadeusz , Stańco Mariusz
Published: June 2010

Determination of centre of gravity of rotational handling machines with the rail undercarriage can be conducted by the measurement of rails strains induced by the wheels of driving machine. At the properly selected combination of superstructure locations with respect to undercarriage, it is possible to eliminate the systematic measurement failures. Determination of centre of gravity is necessary for proper weighing of the machine and selection counterweight. Otherwise it can cause the loss of stability or fast degradation of superstructure rotation bearing.
Effects of land use and riparian flowpath on delivery of dissolved organic carbon to streams
Authors: Findlay Stuart , Quinn John M. , Hickey Christopher W. , Burrell Greg , Downes Malcolm
Published: June 2010

A set of near‐stream flowpaths in pasture, native forest and exotic pine plantations in New Zealand was sampled to describe differences in dissolved organic carbon (DOC). The quantity and bioavailability of DOC varied among flowpaths in different land uses, with higher concentrations of DOC in near‐stream flow paths than the parent groundwater emerging from the hillslope. Tiles incubated in these waters did not consistently yield higher bacterial growth rates than tiles incubated in groundwaters. DOC composition, measured as fluorescence and absorbance properties and extracellular enzyme fingerprints, differed significantly among land uses and position along flowpath. Differences in riparian vegetation can indirectly affect DOC by altering exposure to ultraviolet radiation. A 2‐h exposure of water from subsurface flowpaths to full sunlight caused marked changes in fluorescence characteristics of water from the pasture catchment but only small changes in water from the native forest catchment. There were up to fivefold differences in extracellular enzyme activities on tiles incubated in light‐exposed water for the native forest site, but not for the pasture site. Bacterial growth and respiration were higher on tiles incubated in native forest water exposed to sunlight, but there was no light effect on growth for tiles incubated in water from the pasture flowpath. These results indicate that riparian flowpaths will affect the quantity and character of DOC delivered to streams and ultraviolet exposure may, at least in some cases, alter DOC bioavailability.
Effects of N: P ratio and total nutrient concentration on stream periphyton community structure, biomass, and elemental composition
Authors: Stelzer Robert S. , Lamberti Gary A.
Published: June 2010

The effects of nutrient ratios on algal community structure and algal growth have been examined extensively in lakes and marine environments, but rarely in streams. We manipulated stream water N: P ratio (65 : 1, 17 : 1, 4 : 1) and total nutrient concentration (low and high) in a factorial experiment using once‐through streamside flumes and measured responses in abundance, community structure, and elemental composition of periphyton communities. Early in the experiment, periphyton chlorophyll a and total algal biovolume were higher for treatments where N was added (high total nutrient concentration) but were not affected by N: P ratio. This response is contrary to our prediction that P would limit periphyton growth based on the high N: P ratio in the source water and unamended periphyton mats. The relative abundance of nine of eleven common algal taxa was affected by N: P ratio, total nutrient concentration, or both. Overall, algal community structure was more sensitive than bulk measures of periphyton abundance to changes in N: P ratio and total nutrient concentration. Periphyton %N and %P increased with the N and P concentration of stream water, and periphyton N: P tracked stream water N: P ratio. Responses in periphyton chemical composition to nutrients could affect the food quality of periphyton for consumers.
Distribution and behavior of dissolved hydrogen sulfide in hydrothermal plumes
Authors: Radford-Knoery Joël , German C. R. , Charlou J.-L. , Donval J.-P. , Fouquet Y.
Published: June 2010

Through the deep ocean, hydrothermal plumes disperse high concentrations of key chemical tracers including He‐3, CH4, Mn, Fe, H2S, etc. This paper focuses on the distribution and behavior of total dissolved sulfide (sulfide hereafter) in hydrothermal plumes to show that its plume concentration decreases to subnanomolar a few kilometers from the vents. We also report on sulfide removal rates determined at in situ conditions; we observe that they are two orders of magnitude greater than for open ocean seawater, consistent with sulfide being detected only in the vicinity of hydrothermal vents. From our observations, we infer that the sole presence of sulfide in hydrothermal plumes locates active venting at the kilometer scale.
The metabolic balance of the planktonic community in the North Atlantic Subtropical Gyre: The role of mesoscale instabilities
Authors: Gonzále Natalia , Anadón Ricardo , Mouriño Beatriz , Fernández Emilio , Sinha Bablu , Escáne José , de Armas Demetrio
Published: June 2010

We have studied the net community production (NCP) balance in the Eastern region of the Subtropical North Atlantic during two cruises, in August 1998 and April 1999. In August, heterotrophic bacteria were more abundant than picophytoplankton, which resulted in net heterotrophy (NCP = –129 mmol O2 m−2 d−1 ± 18; mean ± SE), whereas these differences in plankton components were not apparent in April 1999, when the community was in metabolic balance (NCP = –13 mmol O2 m−2 d−1 ± 19). In April, the metabolic balance of microplankton communities was net heterotrophic outside (NCP = –57 mmol O2 m−2 d−1 ± 26) and lower than inside (NCP = 19 mmol O2 m−2 d−1 ± 19) the mesoscale structures present in the area (subtropical front, cyclonic eddy Leticia, and the Great Meteor Tablemount). Positive NCP inside the cyclonic eddy (NCP = 20 mmol O2 m−2 d−1 ± 17) was due to lower respiration rather than to higher gross primary production rates. Gross extrapolation suggests that the regional organic carbon deficit within the Eastern Subtropical Gyre (0.98–1.88 Gt C yr−1) should increase by ~14% and 52% in the absence of mesoscale structures.
Turbulence avoidance: An alternate explanation of turbulence‐enhanced ingestion rates in the field
Authors: Franks Peter J. S.
Published: June 2010

Field observations supporting the hypothesis that wind‐driven mixed‐layer turbulence enhances the prey ingestion by larval fish tend not to have the resolving power to distinguish an alternative hypothesis: that the fish larvae and their prey avoid the turbulence by swimming or sinking downward to the calmer waters, thereby enhancing their concentrations and increasing encounter rates of predator and prey. Here, evidence is supplied supporting the notion of the turbulence‐avoidance hypothesis, and some rough calculations are made to estimate the conditions under which it might apply, how large its effect might be, and the types of organisms that might benefit from it. It is suggested that the turbulence‐avoidance behavior could lead to significant increases in predator and prey concentrations below the mixed layer only hours after the onset of wind‐driven mixing. Larger larval and juvenile fish are expected to benefit the most from such a behavior because they are stronger swimmers and eat larger prey, which might also exhibit the turbulence‐avoidance behavior.
The relative importance of fish predation and excretion effects on planktonic communities
Authors: Attayde José Luiz , Hansson Lars-Anders
Published: June 2010

The effects of planktivorous fish on lower trophic levels through predation on zooplankton and nutrient excretion were experimentally separated and their relative importance quantified in a eutrophic humic lake. The experiment was performed in 12 enclosures (3 m3), which initially were identical with respect to all components except fish. At the start of the experiment, caged fish not able to feed on zooplankton were added to four of the enclosures (excretion treatment), and free swimming fish to four enclosures (excretion plus predation treatment). Four enclosures were left as controls. Samples for nutrients and all major groups of organisms from bacteria to zooplankton were taken after 14 and 28 d. The effect sizes of fish excretion and predation were calculated for each variable. Our results suggest that in eutrophic lakes fish predation on zooplankton may be more important than nutrient excretion by fish for the structure and dynamics of planktonic communities. Fish predation on zooplankton was the most important mechanism accounting for fish effects on nutrient concentrations in the water, on phytoplankton biovolume, on rotifers and total zooplankton biomass, as well as on protozoan densities. However, our results suggest that nutrient excretion by fish may have important indirect effects on zooplankton. Hence, the effects of planktivorous fish through both predation on zooplankton and nutrient excretion act in concert and may be quantitatively important to shape the structure and dynamics of planktonic communities.
On the usefulness of bilateral comparison to tracking turbulent chemical odor plumes
Authors: Webster D. R. , Rahman S. , Dasi L. P.
Published: June 2010

This article reports on the usefulness of bilateral comparison of chemosensory information to an animal or agent tracking an odor to its source. Instantaneous concentration fields of a chemical plume diffusing in a fully developed, turbulent, open channel flow are measured using planar laser‐induced fluorescence. The plume is released isokinetically 25 mm above the smooth bed (z′ = 90), thus transport is mainly due to advection and ambient turbulence. A spatial cross‐correlation function in the spanwise direction gives a strong indication of the relative position of the centerline and distance from the source. The relative direction of the plume centerline can be estimated from the instantaneous concentration, provided the sensors are separated by a distance larger than the spanwise integral length scale of the concentration field.
Natural variability of carbon dioxide and net epilimnetic production in the surface waters of boreal lakes of different sizes
Authors: Kelly Carol A. , Fee Everett , Ramlal Patricia S. , Rudd John W. M. , Hesslein Raymond H. , Anema Cory , Schindler Eva U.
Published: June 2010

The variability of surface water carbon dioxide concentration, or partial pressure (pCO2), was studied in 11 lakes of greatly varying size (2.4 ha up to 8 million ha) in Northwest Ontario, Canada. Six of these lakes were chosen to be as similar as possible in all respects except surface area (the Northwest Ontario Lake Size Series [NOLSS], which range from 88 to 35,000 ha). Spatial and temporal variability of pCO2 within a single lake was no greater in the larger lakes than in the smaller lakes. Interannual variability was significant and synchronous, which indicates that weather patterns were important and affected the different lakes within the region in a similar manner. However, annual pCO2 averages were not related to annual differences in planktonic photosynthetic activity, measured by 14CO2 fixation. In the six NOLSS lakes, there was not a significant relationship of average pCO2 with lake size. For all 11 lakes, however, there was a significant negative correlation of pCO2 with lake size, which was likely due to several characteristics of the very small and very large lakes that covaried with size. The larger lakes were deeper and had longer water residence times and lower DOC, which suggests lower CO2 production from allochthonous organic carbon inputs. Also, the ratio of epilimnetic sediment area/epilimnetic volume (Ae/Ve) was smaller in the larger lakes, which likely resulted in lower rates of recycling of fixed carbon to CO2 during summer stratification.
Relationships between Q‐factor and seawater optical properties in a coastal region
Authors: Zibordi Giuseppe , Berthon Jean-François
Published: June 2010

The Q‐factor—the ratio between upwelling irradiance and upwelling radiance—describes the bidirectional structure of seawater apparent optical properties as a function of geometry and of marine and atmospheric optical characteristics. A 3‐yr time series of Qn(λ) measurements—the Q‐factor determined by nadir radiance—from the North Adriatic Sea coastal waters, has been analyzed. Scatter plots of Qn(λ) versus sun zenith, θ0, for different intervals of the diffuse attenuation coefficient Kd(λ) have shown a consistent exponential trend. In addition, leastsquares regressions of Qn(λ) versus Qn(490) have exhibited determination coefficients R2 that vary from 0.77 to 0.94 in the spectral range between 412 and 555 nm and R2 = 0.50 at 665 nm. To account for these findings, an empirical model for Qn(λ) as a function of θ0 and Kd(λ0) at the reference wavelength λ0 = 490 nm is proposed for North Adriatic coastal waters.
Occurrence and ecological implications of pyrophosphate in estuaries
Authors: Sundareshwar P. V. , Morris J. T. , Pellechia P. J. , Cohen H. J. , Porter D. E. , Jones B. C.
Published: June 2010

Loading of bioavailable phosphorus, traditionally measured as soluble reactive phosphorus (SRP), contributes to the eutrophication of aquatic ecosystems. However, polyphosphates are also bioavailable but escape detection by the standard method used for measuring SRP. 31P nuclear magnetic resonance spectrometric analysis of sediment extracts and enzymatic assay of surface waters reveal heretofore unreported presence of pyrophosphate (Ppi) in coastal wetlands. We show that the accumulation of Ppi (the smallest chemical form of polyphosphate) in coastal wetlands is related to human impact and can occur in quantities that exceed that of SRP. We further demonstrate that Ppi is readily utilized by microbes in coastal wetland sediments in the presence of nitrogen and carbon and can serve as a reservoir of orthophosphate. Thus, Ppi accumulation in estuaries will subsidize the in situ biogeochemical phosphorus cycle. This has important ecological implications for trophic responses and estuarine productivity.
Latitudinal variation of the balance between plankton photosynthesis and respiration in the eastern Atlantic Ocean
Authors: Serret Pablo , Robinson Carol , Fernández Emilio , Teira Eva , Tilstone Gavin
Published: June 2010

A knowledge of the balance between plankton gross primary production (GPP) and community respiration (CR) in the open ocean is vital to the accurate determination of the global carbon cycle, yet the paucity of open ocean measurements severely limits our understanding. This study measured GPP, net community production, dark CR, and size‐fractionated primary production in the upper 200 m of a 12,100 km latitudinal (32°S‐48°N) transect in the Eastern Atlantic Ocean during May and June 1998. This comprehensive data set, which spans five contrasting plankton regimes, including two open ocean oligotrophic provinces, is used to derive a GPP:CR relationship, which suggests that net heterotrophy (GPP , CR) prevails in the eastern Atlantic when primary production falls below ~100 mmol O2 m−2 d−1. The predictive capability of this relationship is compared with that of the only other published relationship based on similar methodologies and is found to give a more representative description of the autotrophic (GPP > CR) to heterotrophic seasonal cycle in the Bay of Biscay. This improved predictive power is attributed to the increased representativeness of the current data set. Specifically, the interpretation suggests that the influence of community structure on net ecosystem metabolism implies that prediction of GPP:CR balances in pelagic ecosystems can be best achieved by use of a data set that covers a wide range of community structure and not only a wide range in the magnitude of primary production.
Production‐respiration relationships at different timescales within the Biosphere 2 coral reef biome
Authors: Falter James L. , Atkinson M. J. , Langdon Chris
Published: June 2010

Temporal relationships between organic carbon production and respiration are not well understood in coral reef ecosystems. We monitored dissolved oxygen (O2) concentrations within the Biosphere 2 coral reef biome over a 3‐yr period (1 January 1997–1 January 2000), to calculate daily rates of gross production (P), community respiration (R), and net community production (NCP). P averaged 170 mmol O2 m−2 d−1, and R averaged 173 mmol O2 m−2 d−1, which yielded a mean NCP of only ‐3 mmol O2 m22 d21, or a difference of only 2%. This long‐term balance between P and R reflects the closed‐system design of the biome. The SD of P, however, was ±56 mmol O2m−2 d−1; that of R was ±47 mmol O2 m−2 d−1; and that of NCP was ±26 mmol O2 m−2 d−1 or ±15% of mean P. To better resolve the behavior of P, R, and NCP at different timescales, each of these time series were spectrally decomposed into four frequency bands that corresponded to four timescales: <1 week, 1 week‐1 month, 1–3 months (subseasonal), and >3 months (seasonal to annual). At timescales >1 month, the variance of P was not different from the variance of R. At timescales of <1 month, the variance in P was significantly greater than the variance in R (P < 0.01). Furthermore, the correlation between changes in P and changes in R became weaker with decreasing timescale. We suggest that changes in P and R become well matched at timescales that coincide with the turnover of carbon by the dominant macroalgae within the biome (1–3 months). In addition, we conclude that measurements of NCP based on daily or weekly data sets are not good indicators of the long‐term net metabolic performance of coral reefs.
Colony formation in Scenedesmus: No contribution of urea in induction by a lipophilic Daphnia exudate
Authors: Lürling Miquel , Elert Eric Von
Published: June 2010

The common green alga Scenedesmus may respond morphologically to numerous environmental factors. The formation of colonies in Scenedesmus resulting from exposure to grazer (Daphnia) excreta is of particular interest since the induced colony formation may be an induced defense. Recent studies suggested that unicell‐colony transformation in Scenedesmus could result from urea released by actively feeding Daphnia and/or by a more lipophilic substance that could be retained by lipophilic solid phase extraction (C18‐SPE). We investigated the generality of the contribution of urea to the overall morphogenetic activity by separating urea and the more lipophilic infochemical using C18‐SPE. No morphogenetic effect of urea was detected in two different algal growth media, whereas Daphnia water induced colony formation. After C18‐SPE of active Daphnia water, the urea containing run‐through was inactive, whereas the desorbed eluate remained active. Thus, colony‐inducing activity is more lipophilic than urea‐related.
Effects of dietary phosphorus deficiency on the abundance, phosphorus balance, and growth of Daphnia cucullata in three hypereutrophic Dutch lakes
Authors: DeMott William R. , Gulati Ramesh D. , Donk Ellen Van
Published: June 2010

We studied population dynamics, phosphorus balance, and individual growth to evaluate limitation of Daphnia cucullata by dietary phosphorus (P) in three interconnected, hypereutrophic Dutch lakes. Consistent with the P‐limitation hypothesis, declines in egg production and population density coincided with seasonal increases in the seston C: P ratio from 300 to 400–500 (molar) in all three lakes. Adult Daphnia collected from Lake Breukeleveen exhibited a linear increase in specific P content during the first 36 h of feeding on a P‐rich diet in the laboratory (r2 = 0.99), which confirms that field Daphnia experienced P deficits in their tissues. Laboratory experiments tested the growth of juvenile D. cucullata in controls with natural seston and in seston supplemented with phosphate or the P‐rich cyanobacterium Synechococcus. Growth was also estimated in filtered lake water with Scenedesmus (2 mg C L−1) as food. This design allowed us to partition differences between the control and Scenedesmus growth rates into limitation by phosphorus, energy and residual factors. In each of 10 experiments, D. cucullata exhibited improved growth in response to the phosphate and Synechococcus supplements. In agreement with predictions, Daphnia exhibited the lowest control growth rate and the strongest response to P addition in seston from the lake with the highest seston C: P ratio. However, animals in seston from two lakes with very similar seston C: P ratios differed in their growth responses. Our results confirm dietary P limitation but show that energy limitation and residual factors also contributed to between‐lake differences in Daphnia growth.
Carbon and nutrient deposition in a Mediterranean seagrass (Posidonia oceanica) meadow
Authors: Gacia Esperança , Duarte Carlos M. , Middelburg Jack J.
Published: June 2010

The annual depositional flux of carbon (C), nitrogen (N), and phosphorous (P) to the sediments under a northeast Spain Posidonia oceanica meadow was evaluated, and the sources and fate of the material deposited elucidated. The annual deposition of carbon represented 198 g C m−2 yr−1, 72% of which was derived from the seston and 28% from P. oceanica detritus. The depositional flux was poor in nitrogen (13.4 g N m−2 yr−1) and phosphorous (2.01 g P m−2 yr−1), although comparable to the nutrient inputs required to support the growth of P. oceanica. Remineralization in the sediment only returned 15.6 g C m−2 yr−1, yielding a net carbon accumulation of 182 g C m−2 yr−1. Our results show that in the Mediterranean littoral P. oceanica meadows are important sites of net organic carbon burial, derived from sedimented sestonic particles and seagrass detritus.
Experimental evidence for linkages between infaunal recruitment, disturbance, and sediment surface chemistry
Authors: Marinelli Roberta L. , Woodin Sarah Ann
Published: June 2010

In prior studies, we have argued that changes in sediment surface chemistry driven by biotic and physical disturbance affect recruitment decisions of infauna. Here, we provide additional data for oxygen concentrations and infaunal recruitment behavior and a time‐dependent numerical model of oxygen concentration in disturbed sediments to further support our proposed linkage between disturbance, sediment chemistry, and recruitment decisions. We evaluated the recruitment responses of the polychaete Arenicola cristata and the bivalve Mercenaria mercenaria to sediments that were undisturbed, disturbed, and allowed to recover for a specified period of time. We also obtained fine‐scale measurements of oxygen concentration in surficial sediments and profiles in the upper sediment layer that new recruits explore. Undisturbed sediments were characterized by high oxygen levels and were readily accepted by recruiting organisms. Disturbance caused dramatic changes in surface and subsurface oxygen concentrations and was accompanied by nearly complete rejection of habitats by new recruits. Oxygen concentrations in cores that were disturbed and allowed to recover are consistent with the time scales of recovery as predicted by a transport‐reaction numerical model. In addition, organism responses to recovering cores varied with oxygen concentration in the surface and subsurface sediments of these cores. The rapid recovery of cores suggests that diagenetic transport‐reaction processes that determine pore‐water composition drive the acceptability of sediments to new recruits.
Sediment geochemical records of eutrophication in the mesohaline Chesapeake Bay
Authors: Zimmerman Andrew R. , Canuel Elizabeth A.
Published: June 2010

An organic geochemical analysis of sediments in three cores from the mesohaline Chesapeake Bay was carried out to reconstruct the progression of eutrophication and anoxia/hypoxia over the past five centuries. Evidence of eutrophication was found in the stable isotopic and lipid biomarker signatures of organic matter in sediments of these cores beginning in the late 18th and early 19th centuries and continuing to the present. Enrichments in the carbon and nitrogen isotopic signature of these sediments likely result from enhanced primary productivity and nitrogen recycling, respectively, and occur, coincidentally, with increased fluxes of total organic carbon (TOC) and episodic enrichments (relative to TOC) of algal and bacterially derived lipid biomarker compounds. More extreme and enduring changes from the late 19th century to the present are indicated by up to fivefold increases in TOC accumulation and 2ߚ to 10ߚfold enrichments (relative to TOC) in algal and bacterially derived lipid biomarker compounds. Increased dinoflagellate and other nondiatom algae relative to diatom production is indicated by lipid biomarker compound ratios. Increases in the ratio of acid‐volatile sulfur to chromiumߚreducible sulfur in sediment indicate the first occurrence of anoxia/hypoxia in 1790 at the deepest site (26 m), and in 1915 at a site 15 m deep. The history of Chesapeake Bay productivity is reconstructed using a diagenetic model to estimate the amount of TOC and biomarker compounds lost to degradation. It is estimated that both TOC delivery and algal and bacterial production have increased by 150% or more relative to preߚColonial times with a temporal progression similar to anthropogenic alteration of the watershed.