bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Surface Defects of Wheel and Rail for Korean High-Speed Railway
Authors: Lee Chan Woo , Kwon Seok Jin
Published: June 2010

Wheels of the railway vehicle play the important role for driving train through wheel-rail interaction. Especially wheel profile is one of the most important design factors to rule the running stability and safety of train. Accordingly, the control of rolling contact fatigue-related defects is an ongoing concern for both safety and cost reasons. This process is referred to as ratcheting. Wear of wheel and rail surfaces occur due to a mixture of adhesive, abrasive and corrosive processes. In wheel/rail systems with little wear, such failure is manifested by the appearance of closely spaced micro-cracks. In the present paper, a evaluation of surface defects of wheel and rail for Korean high-speed railway. The main research application is the wheel-rail maintenance of Korea high-speed train.
The Potential of HAZ Property Improvement through Control of Grain Boundary Character in a Wrought Ni-Based Superalloy
Authors: Hong Hyun Uk , Kim In Soo , Choi Baig Gyu , Jeong Hi Won , Seo Seong Moon , Yoo Young Soo , Jo Chang Yong
Published: June 2010

The effects of grain boundary serration on grain coarsening and liquation behavior in simulated weld heat-affected-zone (HAZ) of a wrought Ni-based superalloy Alloy 263 have been investigated. Recently, the present authors have found that grain boundary serration occurs in the absence of adjacent coarse γ' particles or M23C6 carbides when a specimen is direct-aged with a combination of slow cooling from solution treatment temperature to aging temperature. This serration leads to a change in grain boundary character as special boundary based on the crystallographic analysis demonstrating that the grain boundaries tend to serrate to have specific segments approaching to one {111} low-index plane at a boundary. The present study was initiated to investigate the interdependence of the serration and HAZ property with a consideration of this serration as a potential for the use of a damage-tolerant microstructure. It was found that the serrated grain boundaries suppress effectively grain coarsening, and are highly resistant to liquation cracking in HAZ due to their lower tendency to be wetted and penetrated by the liquid phase. These results reflect closely a significant decrease in interfacial energy as well as grain boundary configuration by the serration.
The Influence of Supply Voltage Amplitude Variation Law on AC Induction Motor Efficiency in Variable-Speed Drive
Authors: Bleizgys V. , Baskys A.
Published: June 2010

This paper presents investigation results of the influence of the supply voltage amplitude variation law on the efficiency of AC induction motor in variable-speed drive based on the frequency converter. It is demonstrated that the commonly employed linear and square voltage amplitude variation laws do not provide the highest efficiency of the AC induction motor. The corrected AC voltage amplitude variation dependences for different motor load torque, at which high efficiency of the motor supplied by the frequency converter is maintained, are proposed and discussed. Reported experimental study was performed on a special test bench.
High Resolution High Power Low Frequency Digital-to-Analog Converter
Authors: Puidokas Vytenis , Marcinkevičius Albinas J.
Published: June 2010

The architectural scheme of the designed Sigma-Delta DAC on the FPGA is considered. The place of the interpolator in Sigma-Delta DACs is briefly discussed. The summarized structure of the most common interpolators is presented. More applicable structures of interpolators were suggested and analyzed, providing the comparison with [1]. Having changed the structure of the incomplete interpolator and having optimized the stages, it was possible to improve the characteristic of amplitude frequency response with a smaller number of non-zero coefficients and much lower FPGA resources. The paper provides simulated results of the interpolator filter transmission characteristics as well as Sigma-Delta modulator quantization noise parameters. It is demonstrated that simulation of the complete converter system (interpolator + modulator + output filter) allows to identify places of the interpolator, where hardware resources could be saved, thereby reducing the chip area occupied by the converter, which is not always obvious when analyzing nodes separately. Therefore another version of the interpolator was proposed for the system ensuring larger suppression of the additional frequency band in the whole system compared with the previous interpolator. Simulated results related to occupied chip resources are also confirmed by the experiment, which was implemented in Xilinx Spartan FPGA.
RFID and Wireless Sensor and Actuator Networks in Advanced Production Applications
Authors: Tervonen Jouni , Luimula Mika , Pieskä Sakari , Pitkäaho Tomi , Alaspää Juha
Published: June 2010

In this study we focus on adding wireless intelligence to machines and systems to be used in production applications. The key enabling technologies of piloted mechatronic systems were RFID (Radio-Frequency Identification) and WSAN (Wireless Sensor and Actuator Network). This work is mainly done in a project “Ubiquitous Computing in Maintenance Using Sensors and RFID Tags”. There were several industrial partners in the project. The main goal is to develop solutions that are suitable for industry. Several systems piloted in harsh industrial environments are considered in the paper.
Application of Non-Linear Correction Systems for Control of Work Movements of the Mobile Crane under a Threat of Stability Loss
Authors: Janusz Jarosław , Kłosiński Jacek
Published: June 2010

A payload displacement in mobile cranes is performed via an adequate composition of working movements. Hoists are used for lifting and lowering of a payload. The following devices are used for displacement of a payload from initial point to another one: a mechanism for generation of crane slewing motion and a mechanism of reach variation. Displacement of heavy payloads by mobile cranes in some conditions can lead to a loss of stability. In this paper authors propose assessment of a stability surplus via: monitoring of values of stress forces of the supports on the ground, calculation of the vertical resultant force of these stress forces and determination of the acting point of the resultant force. The mathematical model of the control system (regulating chassis slewing motion) integrated in the intervention system of a jib reach is presented. Finally, some representative results of numerical simulations are provided.
Rigid Finite Element Modeling for Identification of Vibrations in Elastic Rod Driven by a DC-Motor Supplied from a Thyristor Rectifier
Authors: Lipiński Krzysztof , Kneba Zbigniew
Published: June 2010

The paper deals with the numerical analysis of electromechanical systems. The system consists of a DC motor supplied from a half-wave, single phase, thyristor rectifier, and of a flexible rod fixed to the axis of armature. Discretization of rigid segments is used to model flexibility of the rod. The discrete structure is considered as a multibody system, i.e. as a single kinematical chain of rigid bodies connected by massless joints. Significant drift rotation is included in the rod model. Numerical integration is performed in order to predict behavior of the system. Two working conditions are tested: steady-state motion and transient braking of the system. The attention in the paper is concentrated on interactions between the mechanical and electrical systems.
Improvement of Precise Angle Control System
Authors: Šakalinis Sigitas , Udris Dainius
Published: June 2010

The main task of this research was improvement of precision of positioning drive, installed in a test rig for testing and calibration of the geodetic instruments at Institute of Geodesy of Vilnius Gediminas Technical University. Replacement of a stepper motor and a microstepping controller design increased positioning accuracy up to 0.1. Vibrations and noise of the test rig were significantly reduced using an optimized control algorithm, where resonating step frequencies were bypassed. Time of scale rotation between measurements (every 30) reached less than 1.5 min. Methods for further precision improvement were evaluated and this research is currently in progress.
Verification of Multilayer Neural-Net Controller in Manipulator Tracking Control
Authors: Żylski Wiesław , Gierlak Piotr
Published: June 2010

In this paper a multilayer neural-net (NN) controller is applied for tracking control of robotic manipulator, which is a nonlinear object having unknown and changeable parameters. Dynamics equations of a rigid manipulator are presented. The NN controller is used for compensating manipulator nonlinearities. The controller is realized in a form of a multilayer NN, which is nonlinear in the weights. The standard delta rule using backpropagation tuning is inadequate, so a term correcting the delta rule as well as a robustifying term is added. The presented control law and tuning algorithm are derived from the Lyapunov’s direct method. Results of the experiment are presented in this paper.
Solar Control Glass
Authors: Altan Hasim , Mohelníková Jitka
Published: June 2010

Solar control glass has applications for windows and glazed facades in order to modify indoor visual and thermal comfort in buildings. The article presents the results of evaluation study of optical properties of selected types of solar control glasses and foils. The spectral transmittance measurements were used as input data for daylight comparative studies, and the consideration of convenience of selected solar control glasses and foils for windows are summarised on the basis of analysis of optical properties.
Polymer-Surface Modification with a-C:N:H Layers Plasma Chemically Deposited in RF CVD and MW CVD Systems
Authors: Przetakiewicz Karol , Tkacz-Śmiech Katarzyna , Boszkowicz Piotr , Jonas Stanisława
Published: June 2010

The paper demonstrates that polymer surface may be modified by means of carbon nitride layers (a C:N:H) formed by Plasma Enhanced Chemical Vapor Deposition method. The layers were deposited from CH4/N2/Ar plasma generated by radio-frequency waves (13.56 MHz) and microwaves (2.45 GHz). A series of experiments enabled determination of technological parameters appropriate to deposit well-adhering and high quality layers on PC, Plexi and PET surfaces. The obtained layers were subjected to structural and chemical composition studies employing energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT IR) techniques. It was established that roughness parameters of the samples with layers were visibly lower than the parameters characterizing the surfaces after pre-treating with Ar plasma and remained on the same level or were slightly lower than those for raw polymer surfaces.
Effect of the Unit Pressure on the Selection Parameters of Intermetallic Coatings NiAl and Ni3Al after Plastic Working
Authors: Dyl Tomasz Cyryl , Starosta Robert , Skoblik Robert
Published: June 2010

Modern materials on intermetallic matrix are in the scope of research of many scientific – research centers in Poland [1]. Intermetallic systematic alloys containing aluminium have high resistance to oxidation, abrasive corrosion and fatigue as well as heat resistance. That is why they are applied in the production of machine parts used in hard service conditions (internal combustion turbine blades, exhaust valves, turbo-blower rotors) [2]. Intermetallic coatings can be obtained by means of plasma spraying. Thermal spraying technology is widely used due to the possibility of increasing the service properties in surface layers (strength property, tribological, anti-corrosive and decorative property) as well as coating application on machine parts elements, on tools for plastic working (forging moulds busters, piston rods, gear wheels teeth, crank journals, valve seats, and combustion engine cylinders) [3, 4]. NiAl and Ni3Al coatings are characterized by high fatigue resistance, heat resistance and considerable corrosion resistance [5]. Coatings obtained by thermal spraying have high surface roughness. Thus, subsequent plastic treatment is advisable for plasma-sprayed intermetallic coatings. Therefore it is vital to define to what extent the change of unit pressure will influence reduction of surface roughness of intermetallic coatings. For this purpose experimental upsetting research was carried out on C45 steel samples having NiAl and Ni3Al coatings for the following unit pressures p = 500 MPa, p = 800 MPa, p = 1100 MPa.
Assessment of FSW Welds Made of Aluminum Alloy AW7075-T651
Authors: Szkodo Marek , Adamowski J. , Sitko Artur
Published: June 2010

This paper summarizes the results of experimental studies in which the aluminum alloy AW7075-T651 was friction stir welded (FSW) using various combinations of process parameters (rotational - R and travel speed - T). Mechanical properties of the test welds were assessed by using static tensile test and Vickers hardness measurement. The temperature of the welded plates was monitored during welding by means of thermocouples placed on both sides of the joint line, 15 mm from the weld axis as well as by using thermo camera. The microstructure, chemical composition and phase identification of the welding joints were examined using optical and scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry (XRD). Investigations revealed that the temperatures at the weld center can reach values close to 550 °C and raised with R/T ratio increasing. It was found that tensile strength of welded joints is not correlated with R/T ratio and averages about 60% to 80% of tensile strength of a base material AW7075-T651. XRD analysis demonstrated that there is also deformation texture in the nugget (WN) and the thermo-mechanical affected zone (TMAZ) with strong dependence on process parameters.
The Effect of the Normalizing Rolling of S355J2G3 Steel Round Bars on the Selected Mechanical Properties of Finished Product
Authors: Laber Konrad Błażej , Dyja Henryk
Published: June 2010

The paper presents investigation results related to the effect of application of round plain bar normalizing rolling on the selected mechanical properties of finished product. The research was carried out for the process of rolling 38 mm-diameter plain round bars made of constructional steel S355J2G3, based on actual specifications used in industrial conditions in a continuous bar rolling mill. In the course of investigation the yield stress, YS, and the tensile strength, TS, were determined. With the aim of evaluating the effect of controlled (normalizing) rolling on the mechanical properties of the considered steel grade, Zwick Z/100 testing machine was employed and analytical relationships were used. On the basis of performed research work it was established that enhancement of mechanical properties of the considered steel can be obtained as a result of application of the normalizing rolling process.
The Influence of the Value of Single Draft on Mechanical-Technological Properties of High Carbon Steel Wires
Authors: Suliga Maciej
Published: June 2010

In this work the influence of value of single draft on mechanical-technological properties of high carbon steel wires was evaluated. For wires drawn with medium single draft (10.4 %, 15.5 % and 26.5 %) the investigation of mechanical-technological properties was performed thereby providing results on yield strength, tensile strength, elongation, contraction, number of twist and number of band. On the basis of numerical analysis of wire drawing process the influence of the value of single draft on inhomogeneity of strain was determined. It was established that in the range of medium single drafts 10-26 % used in drawing process of high carbon steel wires large single drafts cause the increase of their strength properties by deterioration of their plasticity properties. It was demonstrated that the increase of strength properties in wires drawn with larger single drafts is related to the occurrence of higher non-dilatational strain, which cause additional work hardening of material. The theoretical-experimental analysis of drawing of high carbon steel wires enabled evaluation of optimal value of single drafts by which it can be used relatively the most advantageous useful properties of wires. Obtained research results can be applied while designing the production process of high carbon steel wires.
Analysis of Microslips and Friction in the Riveted Joints
Authors: Szymczyk E. , Jachimowicz J. , Derewonko Agnieszka , Slawinski Grzegorz
Published: June 2010

The paper deals with analysis of contact stress fields and relative displacements as well as inspection of fretting phenomena in the neighborhood of mating surfaces of the riveted joint subjected to cyclic loading. The study of micro-local phenomena follows the riveting process analysis. Numerical FE simulations of the upsetting process are carried out to determine the residual stress and strain fields. Nondestructive testing methods are used for validation of numerical results. The contact with friction is defined between the mating parts of the joint. The influence of the initial load and sheet material model is studied. Maximum values of relative displacements are comparatively small but surface condition is strongly affected by sliding movements during cyclic loading. Plastic strain energy is taken into account for more efficient numerical analysis of the fretting wear.
The Course of Microcontrollers Oriented to Practical Skills
Authors: Baskys A.
Published: June 2010

The course of microcontrollers oriented to practical skills that is lectured at the Electronics Faculty of Vilnius Gediminas Technical University is presented and discussed in this paper. This course is dedicated to the students of the Basic studies. The laboratory works and the course project, which are of high importance in obtaining the capability to develop microcontroller-based control systems, play a key role in this course. The Mid-range architecture family of PIC (Peripheral Interface Controller) microcontrollers developed and produced by the Microchip company was chosen as the basis for the studies. The structure of lectures, the description of specifics of laboratory works, the course project and the examination procedure are presented here as well. The answers of students indicate that the course has good appreciation. This course is evaluated positively by the institutions involved in the development of the microcontroller-based devices.
Cyclic Fracture Analysis of Semi-Natural Cast Iron Plate with Metallurgical Defects Layer
Authors: Gutauskas Marius , Bacevičius Jonas , Leonavičius Mindaugas Kazimieras
Published: June 2010

Fatigue fracture of the semi-natural cast iron plate with dross and carbon float defects was analyzed. Crack formation and propagation were traced under the programmable cyclic load of the pure bending. The focuses of the crack and their consistent pattern up to the total fracture were determined. Fracture analysis was performed by using optical and electronic microscopy methods. High-cycle fracture mechanism was established when the number of the cycles exceeded 108. The influence of the microstructure upon fracture process was investigated.
Effects of Vibration Energy Input on Stress Concentration in Weld and Heat-Affected Zone of S355J2 Steel
Authors: Jurčius Aurimas , Valiulis Algirdas Vaclovas , Černašejus Olegas
Published: June 2010

The existence of residual stresses induced by the welding process is an important reason of cracking and distortion in welded metal structures that may affect the fatigue life and dimensional stability significantly [1]. Heat treatment is one of the traditional methods to relieve the residual stresses. But it is often limited by the manufacturing condition and the size of the structures. In this paper a procedure called vibratory stress relief (VSR) is discussed. VSR is the process to reduce and re-distribute the internal residual stresses of welded structures by means of weldment mechanical vibration during welding. Parameters of VSR procedure are described in the paper. Residual stresses on weld bead are measured in three different specimens by X-ray diffraction method. Mechanical tests of welded specimens were also performed with purpose to evaluate VSR effect in weld metal and heat affected zone (HAZ).
Analysis of the Plasticity of High-Carbon Alloy Steel in the Conditions of Hot Plastic Working
Authors: Knapiński Marcin , Kwapisz Marcin , Kawałek Anna
Published: June 2010

This research work presented the analysis of plasticity of high carbon alloy constructional steel in the conditions corresponding to plate rolling in a reversing mill. The deformation and temperature conditions occurring in the real process were reproduced during testing. Plasticity of the steel in the temperature range of 800÷1000oC and for three different strain rates of 0.1, 1.0 and 10 /s was determined in the course of experiments. The research was carried out using the Gleeble 3800 physical simulator of metallurgical processes with the Pocket Jaw module, to estimate the steel plasticity in the uniaxial tension test to the failure strain of the sample. The performed research work enables to determine the optimum temperatures and size of the critical deformations which should be taken into consideration when designing the process of the tested steel rolling in order to avoid formation of internal and external cracks.
Seasonal variation of phosphorus limitation of bacterial growth in a small lake
Authors: Carlsson Per , Caron David A.
Published: June 2010

A series of bioassay experiments were performed from spring to autumn in a small dimictic lake (Deep Pond, Massachusetts) to examine the potential for bacterial growth limitation by organic carbon (glucose), inorganic nutrients (ammonium or phosphate), or both. The experiments demonstrated that phosphorus was the primary element limiting bacterial growth in Deep Pond during a large part of the summer. Significant increases (relative to controls) in bacterial cell volumes, protein production rates, and abundances were observed during 24‐h incubations for samples amended with phosphate alone. Organic carbon was near colimitation for most of the samples, however, and dramatic increases in bacterial abundance and rates of protein production were obtained only when both substances (phosphate and glucose) were added together. There was no evidence for nitrogen limitation of bacterial growth during the study. Temperature was not an important determinant for bacterial production rates above 12°C, but below 12°C temperature acted to mute the effect of nutrient and organic carbon additions on production rates. Bacterial growth was not significantly increased by the addition of any combination of glucose, ammonium, or phosphate below 12°C. A significant, albeit complex, effect of the microbial community on the bacterial response to nutrient/carbon enrichment was apparent in the samples. Substrate/nutrient supply and biomass removal by bacterivores both appeared to play a role in the outcome of the experiments.
Influence of salinity and temperature on the growth and production of a freshwater mayfly in the Lower Mobile River, Alabama
Authors: Chadwick Michael A. , Feminella Jack W.
Published: June 2010

Secondary production of the burrowing mayfly, Hexagenia limbata, was quantified from four sites differing in seasonal salinity within the Lower Mobile River, Alabama, from October 1995 to September 1996. This population was univoltine, with emergence occurring from late May through early August. Comparisons with other populations of this species showed latitudinal trends suggesting that summer temperatures may exceed an upper thermal threshold for growth. Longitudinal differences in riverine salinity (i.e., upriver sites, 0‰; downriver sites, 5.5‰ maximum salinity) explained most of the differences among sites, both for average density (upriver sites, 75.6 mayflies m−2; downriver sites, 2.54 mayflies m−2) and annual production (upriver, 1,669 mg m−2 yr−1; downriver, 46.6 g m−2 yr−1). Laboratory bioassays indicated that H. limbata nymphs could survive elevated salinity (LC50 of 6.3‰ at 18°C; 2.4‰ at 28°C), although growth experiments showed similar growth at 0, 2, 4, and 8‰ salinity treatments. Results from field observations and laboratory experiments demonstrated that these mayflies are tolerant of increases in salinity and showed that individuals surviving the stress of elevated salinity can grow at similar rates as mayflies in freshwater.
Multiyear patterns of fungal biomass dynamics and productivity within naturally decaying smooth cordgrass shoots
Authors: Newell Steven Y.
Published: June 2010

Ascomycetous fungi are predominant secondary microbial producers of the smooth cordgrass (Spartina alterniflora) shoot decay system. A 3‐yr examination of concentrations of living fungal mass (as ergosterol content) in naturally decaying cordgrass, and of instantaneous rates of cordgrass‐fungal production (as rates of incorporation of radiolabeled acetate into ergosterol at a standard temperature of 20°C), was conducted in three salt‐marsh watersheds of Sapelo Island. Though the years of study were climatologically different (e.g., rainfall ranging over a factor ~2), ergosterol content of decaying leaves was not different from year to year, with a grand mean of 371 µg ergosterol g−1 organic mass of decaying system, and there was little difference among yearly average fungal productivities (range = 155–217 µg fungal organic mass g−1 system organic mass h−1 for autumn‐spring data). Significant differences in ergosterol content of decaying leaves were found among marsh watersheds, probably due to differences in nitrogen (but not phosphorus) availability, but these were not large (maximum 1.3‐fold for multiseasonal data), and differences were not found among marsh subsites (short to tall shoot) nor, for the most part, among types or parts of decaying leaves. Season of sampling, however, had a large effect upon fungal biomass and fungal productivity: average ergosterol contents were significantly higher in winter and spring (e.g., 416–554 µg g−1 organic mass of decaying blades) than in summer or autumn (<310 µg g−1). Among the potential reasons for this unexpected pattern of seasonality might be (1) greater access of mycophagous invertebrates and/or bacterial competitors due to higher tides and lower elevation of leaves in late summer and fall, and (2) leaching of leaf digestate during periods of high rainfall and high spring tides. Significant correlations were found between ergosterol content of decaying leaves and mean tidal height for the 3 months before sampling (r = −0.77) and for fungal productivities and 3‐month rainfall (r = −0.62). Grazing of decaying leaves by salt‐marsh periwinkles over the range of snail densities of the study sites (0–85 m−2) gave no clear evidence of depression of fungal biomass or repression of fungal activity, contrary to previous findings for higher snail densities. The calculated seasonal change in living fungal percentage of decaying leaves was from ~6 (summer‐autumn) to 9% (winter‐spring), and in 6‐month fungal production, the change was from 101 to 434 g organic fungal mass m−2 marsh surface.
Spatial and diurnal dynamics of dissolved organic matter (DOM) fluorescence and H2O2 and the photochemical oxygen demand of surface water DOM across the subtropical Atlantic Ocean
Authors: Obernosterer, Ingrid , Ruardij Piet , Herndl Gerhard J.
Published: June 2010

Diurnal dynamics of dissolved organic matter (DOM) fluorescence and hydrogen peroxide (H2O2) concentrations were followed in the upper 100 m of the water column at five stations across the subtropical Atlantic Ocean in July and August 1996. The 10% levels of surface solar radiation for the ultraviolet (UV) B range (at 305‐ and 320‐nm wavelengths) were at 16 and 23 m in depth and for the UVA range (at 340‐ and 380‐nm wavelengths) were at 35 and 63 m in depth, respectively. The DOM fluorescence decreased over the course of the day, whereas H2O2 concentrations increased, especially in the diurnally stratified surface water layers extending to 10‐50‐m depth. In situ H2O2 net production varied between 5.5 nmol L−1 h−1 at 5‐m depth and 1 nmol L−1 h−1 at 40‐m depth, resulting in an H2O2 net production of ~38 µmol m−2 d−1 in the upper 50 m of the water column. Photochemical oxygen (O2) demand of water collected at 10‐m depth in the early morning and exposed to surface solar radiation varied between 0.9 and 2.8 µmol O2 L−1 d−1 and was found to be consistently higher (by a 1.3‐8.3‐fold measure) than bacterial respiration (measured in 0.8 µm‐filtered seawater in the dark). UVB radiation was responsible for 0‐30% of the photochemical O2 demand. A simple one‐dimensional physical model was combined with a photochemical/biological model in order to describe the photochemical production of H2O2 at different depth layers over the course of the day and to determine the contribution of physical versus biological processes in terms of the loss of H2O2 from the surface layers in the late afternoon. The model reflects well the observed diurnal H2O2 dynamics. It further provides evidence that mainly biological breakdown determines the loss of H2O2 in the upper 50 m of the water column during the day; however, in the late afternoon, vertical mixing is important in transporting H2O2 from the uppermost 5‐m layer to the 10‐20‐m layers.
Mesoscale variability of physical and biological fields in southeastern Lake Superior>
Authors: Zhou Meng , Zhu Yiwu , Putnam Shawn , Peterson Jay
Published: June 2010

A cruise was conducted in southeastern Lake Superior east of Marquette, Michigan from 15 to 20 July 1999. A towed, vertically undulating instrument package containing a conductivity‐temperature‐depth (CTD) profiler, a fluorometer, and an optical plankton counter was used for data collection. Results indicated that the concurrent, high‐resolution survey of both physical and biological variables provided the fundamental basis for illustrating the correlation between mesoscale physical and biological fields and for investigating mesoscale physical and biological processes. It was revealed that the high chlorophyll a biomass beneath the thermocline co‐occurs with up‐tilting of the thermocline. This tilting of the thermocline was associated with the thermally driven coastal current. We hypothesize that the up‐tilting of the thermocline lifted deep water into the euphotic zone, leading to high productivity of phytoplankton beneath the thermocline. The presence of both warm water and food provided a favorable physical and biological environment for zooplankton. The abundance of zooplankton reached 10 x 103 individuals m−3 in the warm surface water and was down to 3 × 103 individuals m−3 at a depth of 40 m.
Microbial size spectra from natural and nutrient enriched ecosystems
Authors: Cavender-Bares Kent K. , Rinaldo Andrea , Chisholm Sallie W.
Published: June 2010

Microbial size spectra, including bacteria through nanophytoplankton, were measured by use of flow cytometry across the western north Atlantic Ocean and during two nutrient enrichment studies: bottle enrichments in the Sargasso Sea and an in situ iron enrichment in the equatorial Pacific (IronEx II). Spectral shapes, or the relative conformity to a function described by a power law, ranged from smooth and log linear during the spring bloom in the Sargasso Sea to being distinctly non‐log linear in coastal waters. Overall, the individual spectra within large regions characterized by similar ecological conditions showed remarkable consistency, inviting speculation that powerful organizing mechanisms are at work in these communities. Moreover, the ensemble average of all of the spectra along the transect displays clear power‐law behavior. Slopes ranged from 21.0, in which biomass was equally distributed between all size classes, to 21.4, in which proportionally more biomass was contained in smaller size classes; there was no clear relationship between nutrient concentrations and spectral slopes over the entire data set. Species succession in nutrient‐enriched bottles caused spectra to evolve from relatively smooth power laws to distributions showing preferred sizes (i.e., nonlinear on a log‐log plot). The IronEx II spectra, however, remained similar over the course of the experiment. It could be that the elimination of bottle effects in this experiment buffered the system in ways that maintained the size structure of the microbial community over the size range we measured. Our results suggest conditions that lead to log‐linear size distributions; these should be verified over a broader range of scales and environments.
Assessment of photosynthesis in a spring cyanobacterial bloom by use of a fast repetition rate fluorometer
Authors: Suggett David , Kraay Gijsbert , Holligan Patrick , Davey Margaret , Aiken Jim , Geider Richard
Published: June 2010

Estimates of gross primary production (GPP) based on fast repetition rate fluorometer (FRRF) measurements were compared with independent 14C and O2 at three stations during a spring bloom in the North Atlantic. A photosynthesis versus irradiance (P‐E) curve was constructed for each station from the observations of in situ photon efficiency of photosynthesis. This composite P‐E curve was compared with P‐E curves determined for discrete samples from 14C assimilation. Estimates of aChl and PmChl from the 14C‐uptake method were 1.5–2.5‐fold lower than those estimated from the FRRF data. Much of this discrepancy can be accounted for if 14C assimilation approximates net phytoplankton photosynthesis with use of a photosynthetic quotient of 1.4 mol O2 (mol CO2)−1. Photosynthetic oxygen consumption may have also contributed to the difference. In situ GPP was calculated from incident irradiance, light attenuation, light absorption by phytoplankton, and the light dependence of the in situ photon efficiency. This estimate of GPP was two times greater than net community photosynthesis determined from diel changes of in situ oxygen concentration. Thus, the in situ net O2 and in vitro 14C techniques yielded similar estimates of phytoplankton photosynthesis that were about twofold lower than the estimates of GPP provided by FRRF. Uncertainties in the FRRF technique associated with choosing an appropriate value of photosynthetic unit size and fitting a P‐E curve to the in situ measurements are discussed. Despite these uncertainties, the FRRF results were consistent with the independent estimates of phytoplankton productivity.
Massive developments of microbial mats following phytoplankton blooms in a naturally eutrophic bay: Implications for nitrogen cycling
Authors: Graco Michelle , Farías Laura , Molina Verónica , Gutiérrez Dimitri , Nielsen Lars Peter
Published: June 2010

Benthic nitrogen processes have received substantial attention because the release of nutrients from sediments can contribute to the requirements of pelagic primary production; their study can also give an estimation of the importance of the sediment as a source or a sink of nutrients. Concepción Bay is located in central Chile and is the largest (167.4 km2) and most enclosed embayment on the Chilean coastline. The bay is characterized by a strong hydrographic variability produced by the spring/summer seasonal upwelling of Equatorial subsurface waters (ESSW), rich in nutrients (~25 µM NO3−) and poor in oxygen (≪44.6 µM). The area was studied in order to understand the consequences of phytodetrital deposition and oxygen deficiency on the environment and benthic communities. The study was carried out by sampling at a single station (28‐m depth) in the inner part of the bay during winter (June 1998) and spring/summertime (November 1998 and January and March 1999). It was focused on measurements of benthic nitrogen fluxes, sulfate reduction, and denitrification rates before and after a phytoplankton bloom. Additionally, samples from the flocculent layer and from a semipurified bacterial mat were incubated under controlled oxygen conditions to determine NH4+ production. NH4+ exchange showed a clear seasonal pattern, with influxes during the winter (27.6 ± 4.9 mmol m−2 d−1) and high effluxes during the summer (36.6 and 20.8 mmol m−2 d−1) when the accumulation of fresh organic matter (evidenced as chlorophyll a) produced a flocculent layer over the sediments. Besides natural hypoxia of the bottom water associated with ESSW, the large input of organic matter resulted in anoxia within the sediment, as a consequence of respiration processes, and an enhancement in sulfate reduction rates (up to 200 mmol m−2 d−1). The flocculent layer then provided a favorable environment for the extensive development of Beggiatoa spp. mats. Overall, during the sampling period, NO3− was consumed at an average rate of 1.33 mmol m−2 d−1. In the summer, denitrification appeared to be partially inhibited by the very negative redox conditions and could explain only 24% of the NO3− uptake by the sediment. The balance may be due to NO3− incorporation into Beggiatoa spp. Short incubations with these bacteria suggest that they are able to produce NH4+ by dissimilatory NO3− reduction, taking advantage of their ability to store NO3−, though its uptake was not observed in these experiments. The NH4+ flux obtained using Beggiatoa spp. mat cultures was 5 mmol m−2 d−1, which accounts for 17% of the total NH4+ efflux during the summer period (January and March). The ecological implications of a large input of organic matter, evidenced by the presence of a flocculent benthic layer and Beggiatoa spp., are discussed in relation to their contribution, during the upwelling season, toward the long‐term eutrophication of Concepcion Bay.
Shifts in habitat templates for lotic microalgae linked to interannual variation in snowmelt intensity
Authors: Peterson Christopher G. , Valett H. Maurice , Dahm Clifford N.
Published: June 2010

We investigated the importance of snowmelt as an organizing factor for epilithic microalgae in a high‐altitude montane stream during 3 yr (1995–1997) of differing melt characteristics. Changes in algal biomass and taxonomic structure in two stream reaches that differed in hydrologic characteristics were assessed relative to variation in stream‐water nutrient content, temperature, surface‐water/groundwater exchange, and algivorous macroinvertebrate assemblages. Melt‐induced increases in stream discharge were large and abrupt in 1995, nearly undetectable in 1996, and protracted and of intermediate magnitude in 1997. In 1995, algal and grazer densities were significantly reduced by melt discharge. Postmelt grazer recovery was slow, and the percentage of live cells in the diatom assemblage increased abruptly; algal biomass initially increased and subsequently varied with stream‐water N: P ratio. In 1996, snowmelt produced no evident proximate effects. Initial high grazer densities declined throughout the summer. In midsummer, an N: P ratio of 140 in the upstream reach corresponded to a more than fourfold increase in algal biovolume and a shift to dominance by large diatoms. Downstream, a lower N: P peak induced no algal response. In 1997, grazer densities declined during protracted melt runoff and increased sharply during melt recession, concurrent with decreases in live diatom percentage and algal biovolume. N: P declined in 1997 from ~16 : 1 to values indicative of N limitation and correlated with decreases in algal biovolume. Our results show that effects of snowmelt in montane streams reflect both initial melt‐induced mortality that sets initial conditions for succession and melt‐induced aquifer recharge that controls nutrient supply in the months following peak melt discharge. The influence of these two components extends beyond snowmelt recession into summer base flow, suggesting that variation in melt characteristics generates interannual differences in the functioning of these systems.
Evidence of a mutualistic relationship between an algal epibiont and its host, Daphnia pulicaria
Authors: Barea-Arco J. , Pérez-Martínez C. , Morales-Baquero R.
Published: June 2010

We examined seasonality, intensity, and level of epibiont infection by the green alga Korshikoviella gracilipes on the zooplankton community over 2 yr in the high mountain Rio Seco lake. Daphnia pulicaria was the preferred substrate for the epibiont, whose life cycle was exclusively completed on this taxon. The density of epibiont dispersal stage and the epibiont prevalence and burden on crustacean zooplankton were directly related to D. pulicaria density in both years. Laboratory experiments showed that attached epibionts had a negative effect on Daphnia by increasing the weight and sinking rates of infected animals and a positive effect by increasing its reproductive rates, with a neutral effect on survivorship. On the other hand, the epibiont dispersal stage was actively and intensively grazed by Daphnia, which implies a benefit for Daphnia and a cost for K. gracilipes. Thus, both species derived benefits and costs from this relationship. Our results indicate a positive cost‐benefit balance for both epibiont and host in such a way that a mutualistic relationship can be suggested. This epibiont‐host interaction may play an important role in population and community regulation in Rio Seco lake.
Benthic‐Pelagic coupling over a zebra mussel reef in western Lake Erie
Authors: Ackerman Josef Daniel , Loewen Mark R. , Hamblin Paul F.
Published: June 2010

We conducted a field study including a series of cruises over an isolated offshore zebra mussel reef (7–11 m deep) in Western Lake Erie to examine the effect of zebra mussels (Dreissena spp.) on the water column. The horizontal currents over the reef were found to be primarily due to the hydraulic flow and surface gravitational seiches. The turbulence generated by these currents was found to be too weak to fully mix the water column. Although seasonal stratification was not observed, solar heating during the day and intrusions of cold central basin water caused stable stratification of the water column 60% of the time. Results from the seston analysis taken at five depths showed a statistically significant mussel‐feeding signature in chlorophyll a and organic seston concentrations measured within 2 m above the reef. Estimates of clearance rates based on field data were consistent with rates measured in a flow chamber using water from the site, which indicated that zebra mussels could remove up to 40% of the total seston. The detection of a zebra mussel‐induced concentration boundary layer is due to: (1) reduced vertical mixing as a result of semidiurnal periodic stratification, (2) refiltration of bottom water in zebra mussel populations, and (3) in situ clearance rates that are lower than those observed in the laboratory. Thus, offshore zebra mussel colonies may have less of an effect on the water column than had been previously estimated by simple stirred reactor models, and the role of zebra mussels in the clarification of Lake Erie should be investigated further.
Redfield ratios revisited: Removing the biasing effect of anthropogenic CO2
Authors: Körtzinger Arne , Hedges John I. , Quay Paul D.
Published: June 2010

Redfield ratios of remineralization are calculated based on chemical data analysis on isopycnal surfaces. The concentrations of dissolved inorganic carbon used in this study were corrected for the anthropogenic CO2 content as estimated with a back‐calculation technique. The corrections increased the apparent carbon remineralization by 25–30%, thus proving important for the reliable estimation of Redfield carbon ratios in the presence of anthropogenic CO2. Best estimates from this study largely confirm the more recently published Redfield ratios of remineralization. The following results were obtained for the latitude range 3–41°N along 20–29±W in the Northeast Atlantic Ocean: Corg: P ratio = 123 ± 10; Corg : N ratio = 7.2 ± 0.8; —O2 :Corg ratio = 1.34 ± 0.06; —O2 : P ratio = 165 ± 15; N: P ratio = 17.5 ± 2.0. These ratios are in close agreement with the average composition of phytoplankton and represent respiration of organic matter consisting on average of 52% protein, 36% polysaccharide, and 12% lipid.
Rapid nitrogen uptake by marine bacteria
Authors: Goldman Joel C. , Dennett Mark R.
Published: June 2010

In order to test the rapid nitrogen uptake capabilities of marine bacteria, we first grew natural populations in NH4+ and glutamateߚlimited continuous cultures over a range of steadyߚstate dilution rates, to establish different physiological states. We then pulsed the cultures with saturating concentrations of 15Nߚlabeled NH4+ or glutamate and found that rapid uptake, measured as the ratio VM′ : µM (VM′ is the timeߚdependent maximum specific uptake rate of nitrogen, and µM is the maximum growth rate), decreased with time of incubation from ~3–4 at 40 s to <=1 by 5–15 min. Relative growth rate D: µM (D is the steadyߚstate dilution rate) had no systematic effect on this relationship. Although enhanced nitrogen uptake is apparent in marine bacteria, it is far less dramatic than what we and others have observed previously in some marine diatoms: e.g., VM′ : µM > 5–50 has been measured in several diatoms during similar 1‐min incubations, and values >1 have been observed during 2ߚh incubations. These results point toward fundamental differences in the temporal and spatial scales that control the exposure to and ability to exploit ephemeral nutrient patches of marine bacteria and phytoplankton. Bacteria probably are sustained by more frequent and relatively short contacts with smaller nutrient patches both in size and concentration than those experienced by phytoplankton. The latter must overcome greater diffusion constraints because of their larger size. Evidence from recent studies, suggestive that bacteria respond to point sources of nutrients surrounding larger microbes through motility and chemotaxis, is consistent with our finding of moderately enhanced nitrogen uptake by these organisms.