bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Treatment of Aircraft Engine Usage
Authors: Enright M. P. , Hudak S. J. , McClung R. C.
Published: August 2009

The fracture risk of aircraft engine components is sensitive to small changes in the applied stress history. Although standard missions have been developed for design of military aircraft, stress values based on data obtained from flight data recorders can differ significantly from the design values. In this paper, a comprehensive framework is presented for probabilistic treatment of aircraft engine usage that consists of the following four stages: (1) data retrieval, (2) mission identification, (3) stress characterization, and (4) risk prediction. An example is presented that illustrates the approach for a number of actual flight histories. The framework can be applied to quantitative risk predictions of gas turbine engine components for enhanced life management, including potential life extension and associated cost savings.
Harmonic Analysis of Jet Mixing
Authors: Boulanger Joan , Yun Sangsig , Jiang Leiyong
Published: August 2009

Development of low-pollution gas turbine engines has been calling for the development on new technologies. Lean premixed combustion is one of them but tends to be accompanied by combustion instabilities. Some instabilities are caused by coupling between the combustion zone and upstream fuel/air mixing chamber. Acoustic oscillations in the mixing chamber lead to variation of mixture distribution in the combustion zone. On the other hand, the instability itself may improve the turbulent mixing that mitigates these equivalence ratio fluctuations. The goal of this study is to gain knowledge of the fundamental mechanisms of harmonically perturbed jet mixing in air. A jet is considered as a system on which a harmonic analysis is performed. The input parameter is a modulated velocity to induce perturbation. The output parameter is the whole flow field, particularly the statistics of mixture fraction distribution. The tool is a high-order compressible direct numerical simulation code. It is demonstrated that the system can be qualified as a band-pass filter. The efficiency of mixing reaches a maximum for a modulation frequency comparable to the natural mode of a laminar jet. This study suggests that the characteristic frequency of the system to improve mixing can be inferred from the investigation of the natural mode of this system and vice versa.
Verification of the Vibration Amplitude Prediction of Self-Excited LPT Rotor Blades Using a Fully Coupled Time-Domain Non-Linear Method and Experimental Data
Authors: Corral Roque , Gallardo Juan Manuel
Published: August 2009

The vibration level of aerodynamically unstable low-pressure-turbine rotor blades has been assessed for the first time using two-different approaches. Both methods assume that the aerodynamic forcing is due solely to the self-excitation of the airfoil and that the vibration amplitude is saturated due to the non-linearity associated to the fir-tree dry friction, which is modeled using a simplified approach. To compensate for the limitations of the friction model several hypotheses need to be done, among them, the geometric similarity of the different configurations and that the aspect ratio of the rotor blades is high. The first approach, which is novel, assumes that the vibration amplitude is small enough and the unsteady aerodynamics associated to the airfoil motion may be computed using a frequency domain linearized Navier-Stokes solver. The vibration amplitude is obtained posing the energy balance between the energy exerted by the most unstable aerodynamic mode and the energy dissipated by dry friction. The second approach time marches simultaneously the Reynolds-Average Navier Stokes equations and a simple mass-spring non-linear model consistent with the mechanical model used in the first approach. This fully coupled non-linear, both in the aerodynamic and structural sides, flutter analysis is considered unique in its kind. It is demonstrated by means of a simplified, but consistent with typical low-pressure-turbine bladed-disk, model that both methods are equivalent. The first approach has been applied to several bladed-disks and the comparison with experimental data is good in overall.
Fischer-Tropsch Fuel Characterization via Microturbine Testing and Fundamental Combustion Measurements
Authors: Srinivasan A. , Ellis B. , Crittenden J. F. , Lear W. E. , Rotavera Brandon , Petersen Eric L.
Published: August 2009

Synthetic fuels such as Fischer-Tropsch (FT) fuels are of interest as a replacement for aviation, diesel, and other petroleum-based fuels, and the present paper outlines a joint program to study the combustion behavior of FT synthetic fuels. To this end, shock-tube spray and high-recirculation combustion rig experiments are being utilized to study the ignition delay times, formation of soot, and emissions of FT jet fuels. Undiluted shock tube spray experiments were conducted using a recently developed heterogeneous technique wherein the fuel is sprayed directly into the test region of a shock tube. The high recirculation combustion rig is a complete gas turbine system where Syntroleum FT jet fuel was combusted, and soot formation and emission characteristics were observed. Reduction of soot volume fraction and unchanged emissions were observed, in agreement with previous investigations. The fundamental shock tube results were found to be consistent with the observations made in the experimental engine.
Nonlinear Dynamic Behaviors of Rotor Systems for Ball End Milling
Authors: Shiau Ting-Nung , Chen Kuan-Hung , Huang K. H.
Published: August 2009

The nonlinear dynamic behaviors of rotor-bearing system for ball end milling are studied in this paper. The rotor system is supported by bearings with nonlinear spring effects. The nonlinear cutting force can be calculated by using the Tlusty proposed 3/4 rule for chip thickness. The effects of design parameters on system dynamic behaviors including critical speeds and stability under the dynamic cutting forces are numerically investigated in the time domain. For linear system case or the nonlinear system with small depth-of-cut or feed per tooth under linear cutting force, the results show that the critical speeds of system are proportional to the corresponding system natural frequencies, but inversely to the cycle number of tool vibration multiplying by the number of flutes during the cutting time from one flute to another. With large depth-of-cut or feed per tooth, the differences of the critical speeds become larger between linear and nonlinear rotor systems and so are the dynamic responses at critical speeds milling. The critical speed under nonlinear cutting force milling is found to be always higher than that under linear cutting force. Furthermore, the chatter stability lobes are studied for various cutting conditions. The intervals between critical speeds increase gradually, and the axial depths of cut of nonlinear system for stability are lower than those of linear system.
Numerical and Experimental Study of Active Flutter Suppression With Piezoelectric Device for Transonic Cascade
Authors: Watanabe Toshinori , Kazawa Junichi , Uzawa Seiji , Keim Benjamin
Published: August 2009

Possibility of active suppression for transonic cascade flutter with piezoelectric device was studied both numerically and experimentally. In the numerical study, a previously proposed control method in which the blade trailing edges were actively oscillated was analyzed in detail toward realistic application by a developed numerical method with flow-structure coupling. From the results, the effect of the control was confirmed, and the suppression was revealed to come from the appropriate change in the oscillatory behavior of the passage shock. Experimental study was conducted in linear cascade wind tunnel under transonic flow condition to verify that the method realized substantial effect on stability of the blade oscillation. Unsteady aerodynamic forces induced by the active oscillation of a blade on which piezoelectric devices were glued were measured and superposed with the unsteady induced force causing flutter instability. The results showed a distinctive stabilization effect of flutter suppression in the case with appropriate phase difference between original blade vibration and the active oscillation of the piezoelectric device. The active oscillation was, however, found to generate destabilization effect if the phase was inappropriate.
Analysis of Lumped Deterministic Source Terms and Their Sub-Components in a Stage 1 High Pressure Turbine Rotor
Authors: Ratzlaff Jon , Orkwis Paul D. , Noll Christopher , Steuber Gary
Published: August 2009

A GE proprietary code has been used to extract the Lumped Deterministic Source Terms (LDSTs) for the five governing equations: continuity, r, θ, z-momentum, and energy; as well as the two turbulence equations, from a converged unsteady time-averaged flow field. LDSTs are the opposite of the fluxes contained in the solution residuals for a time averaged flow field. They describe the cumulative effects of unsteadiness contained in the time-averaged solution. It has been shown that the addition of these terms to the steady residual operator in this code will drive the solution to the time averaged unsteady solution. The contributions of the LDST components, i.e. the residuals from the Euler, viscous and numerical dissipation, were studied to assess how they build the total LDST. Another approach to computing the inviscid source terms directly from time series data was also compared to the respective total and shows that the LDSTs are composed primarily of the inviscid component terms. In addition, attaining a time-averaged solution with a steady solver has been found to be sensitive to the boundary conditions. Results from one boundary condition set are presented in an error form to gauge the impact on the solution.
Gas-Side Heat Transfer in Syngas, Hydrogen-Fired and Oxy-Fuel Turbines
Authors: Mazzotta Danny W. , Karaivanov Ventzislav G. , Chyu Minking K. , Slaughter William S. , Alvin Mary Anne
Published: August 2009

To meet the performance goals of advanced fossil power generation systems; e.g. FutureGen, future coal-gas fired turbines will need to be operated at temperatures higher than those in the current commercial natural gas-fired systems. The working fluid in these future turbines could contain substantial moisture (steam) mixed with carbon dioxide, instead of air or nitrogen in conventional gas turbines. As a result, the aero-thermal characteristics among these new turbines are expected to be significantly different not only from the natural gas turbines but also dependent strongly on the compositions of turbine working fluids. Described in this paper is a quantitative comparison of thermal load on the external surface of turbine airfoil present in different power cycles the US Department of Energy plans for the next decade. The study is pursued with a computational simulation based on three-dimensional computational fluid dynamics (CFD) analysis. While the heat transfer coefficient has shown to vary strongly along the surface of the airfoil, the projected trends were relatively comparable for airfoils in syngas and hydrogen-fired cycles. However, the heat transfer coefficient for the oxy-fuel cycle is found to be substantially higher, by about 50–60%, than its counterparts in syngas and hydrogen turbines. This is largely attributable to the high steam concentration in the turbine flow. This overall suggests that advances in cooling technology and thermal barrier coatings are critical for the developments of future coal-based turbine technologies with nearly zero emission.
Unsteady Simulations for an Advanced-Louver Cooling Scheme
Authors: Zhang Chad X.-Z. , Kim Sung In , Hassan Ibrahim G.
Published: August 2009

The performance of a louver cooling scheme on a flat plate was analyzed using Detached Eddy Simulation. It was assumed that the louver cooling scheme was tested in a wind tunnel with the mainstream flow velocity of 20 m/s, equivalent to a Reynolds number of 16200 based on the jet diameter. Turbulence closure was achieved by a Realizable k-ε based DES turbulence model. Solutions of two blowing ratios of 0.5 and 1 were successfully obtained by running parallel on 16 nodes on a computer cluster. The instantaneous flow fields were found to be highly unsteady and oscillatory in nature. It is shown that the fluctuations in the adiabatic effectiveness are mainly caused by the spanwise fluctuation of the coolant jet and the unsteady vortical structures created by the interaction of the jet and the mainstream.
Creep Analysis of Cross Wavy Primary Surface Recuperator for Microturbine System
Authors: Zhang D. J. , Zeng M. , Wang J. W. , Wang Q. W.
Published: August 2009

Recuperator in a microturbine system, which must work at high temperature and high pressure, is a key component to improve the electricity efficiency of the system. Creep deformation may occur in the passages of the compact primary sheet with the increase of the operation time. Creep is important in high temperature stress analyses, because over a period of time at high temperature, the preload in the recuperator would decrease (stress relaxation) and potentially let the adjacent parts move. Typically, the creep deformation is permanent. Inside the recuperator creep deformation causes the compressor discharge air passages to expand; thus restrict exhaust gas flow and increase the turbine backpressure. And this has bad effect on the flow and heat transfer performance of the recuperator, even on the safety of the whole system operation. In this paper, with the implicit Norton function supplied by software ANSYS, the creep deformation of cross wavy (CW) recuperators (for 40,000 hours operation) is analyzed to prove the reliability of material and some influencing factors on creep strain are investigated. Five conclusions are obtained: (1) Alloy 0Cr18Ni11Nb is an acceptable material for recuperators. (2) The pressure difference between the air and the gas is the main reason to cause creep deformation of the sheet. (3) The creep resistant alloy with metallic element Nb is good to be used when manufacturing recuperators. (4) The widths of the gas passage must be larger than that of the air passage to balance the deformation of the two sides. (5) A method for finding an optimal thickness is presented. δ = 0.12mm is suggested as the maximum sheet thickness.
Three-Dimensional Stress Analysis and Configuration Optimization of Cross Wavy Primary Surface Recuperator for Microturbine System
Authors: Zhang D. J. , Zeng M. , Wang Q. W.
Published: August 2009

Recuperator in a microturbine system, which has to work under a high temperature and high pressure condition, is a key component to improve the electricity efficiency of the system. High temperature and pressure may cause high stress inside the Cross-Wavy Primary Surface (CWPS) sheet, and it is essential to analyze the stress distribution to ensure the security while the recuperator is working. In this paper the combined thermomechanical design of a CWPS recuperator for a 100kW microturbine system is presented. With the ANSYS Parametric Design Language (APDL), calculation procedures for heat transfer and stress analysis are combined in order to perform a reliable strength prediction of the recuperator. A program has been generated, which allows the automatic generation of the numerical model, the mesh and the boundary conditions. Also with the energy minimum principle, an optimal configuration of the air and gas passages is obtained. The results show that the material of the primary sheet (0Cr18Ni11Nb) is reliable. The stress distribution changes with the different configuration of the passages. Since the air pressure is much higher than that of the exhaust gas, the configuration of the primary sheet is much better when the sectional area of the gas passage is larger than that of the air passage. If the pitch of the sheet is maintained at 2mm, the best configuration is obtained when the dimension of passage is at r = 0.35–0.42mm, R = 0.55–0.48mm.
Design, Development and Test of a 30 kW Oil Free, Turboalternator
Authors: Heshmat Hooshang , Walton James F. , Tomaszewski Michael J.
Published: August 2009

This paper describes the design procedures and testing program used in the development of a 30 kW single shaft permanent magnet turboalternator with compliant foil bearing supports. The development program included design tradeoff studies assessing generator rotor and bearing configurations, design of the turbine, and packaging of the entire system. This paper also describes the test program to assess dynamics, thermal management of the system and testing to assess power output. Test results achieved with the prototype system operating to full speed and under power generating mode will be presented. A comparison between predicted and measured electrical output will also be presented up to a power generating level of 25 kWe at approximately 55,000 rpm. The excellent correlation between design and test provides the basis for scale up to larger power levels. This program demonstrates the successful integration of oil-free foil bearings, 4-pole composite wound permanent magnet alternator, thermal management capabilities and an axial flow turbine.
Systems Level Performance Estimations for a Pulse Detonation Combustor Based Hybrid Engine
Authors: Tangirala Venkat E. , Joshi Narendra D.
Published: August 2009

The Pulse Detonation Combustor (PDC) has recently evoked much interest as a pressure-gain combustor for use in gas turbines. A key application for a Pulse Detonation Engine (PDE) concept has been envisioned as a hybrid power generation engine, which would replace the combustor in a conventional gas turbine with a PDC. Estimations of performance parameters, namely, thermal efficiency (ηth) and specific work (Wnet) are reported for a PDC based hybrid engine for various configurations of the engine. The performance enhancing configurations of the PDC-based hybrid engine, considered in the present study, include simple cycle, intercooling, regeneration and reheat, similar to the configurations for a conventional gas turbine (GT) engine in the literature. The performance estimations for a conventional gas turbine engine and a PDC based hybrid engine are compared for the same operating conditions (such as inlet pressure, inlet temperature, compression ratio, overall equivalence ratio) and for various configurations. The thermal efficiency of an intercooled PDC hybrid engine with regeneration has the highest value for the entire range of turbine pressure ratios, from 1.2 to 40 (corresponding to a compression ratio range of 1 to 30). An intercooled PDC based hybrid engine with reheat produces the highest specific work (Wnet) when compared to all other configurations. Among simple-cycle /regeneration /reheat configurations of a PDC based hybrid engine, ητh for the intercooled PDC based hybrid engines has the highest estimated value (0.47) at a turbine pressure ratio of 30. The intercooled PDC based hybrid engine also produces the highest specific work (Wnet) when compared to simple-cycle/regeneration/reheat hybrid engine configurations over the entire range of turbine pressure ratios.
A Model of Nonlinear Fatigue-Creep (Dwell) Interactions
Authors: Wu Xijia
Published: August 2009

A nonlinear creep/dwell-interaction model is derived based on nucleation and propagation of a surface fatigue crack and its coalescence with creep/dwell damages (cavities or wedge cracks) along its path inside the material, which results in the total damage accumulation rate as given by dadN=1+lc+lzλdadNf+dadNenv where (da/dN)f is the pure fatigue crack growth rate, (da/dN)env is the environment-assisted crack growth rate, lc/lz is the cavity/wedge crack size, and λ is the average spacing between the internal cavities or cracks. Since wedge cracks are usually present in the form of dislocation pile-ups at low temperatures and cavitation usually occurs at high temperatures, the model attempts to reconcile the creep/dwell-fatigue phenomena over a broad temperature range of engineering concern. In particular, the model has been used to explain dwell fatigue of titanium alloys and high temperature creep-fatigue interactions in Ni-base superalloys under TCCR, CCCR, THCR and CHCR test conditions (see Annex A for definition of the terminology).
Performance Prediction of Centrifugal Impellers Using a Two-Zone Model
Authors: Britton Ian , Gauthier J. E. Donald
Published: August 2009

This paper outlines the methodology and theory required for the development of a computer code for the performance prediction of centrifugal impellers. The theory is blended from two main sources on two-zone model development. The equations provided show a simplified version of previous two-zone models published while maintaining a similar level of accuracy in the prediction of pressure ratio and isentropic efficiency. The idea behind the development of the algorithm is the production of an impeller map which can be used in the preliminary design phase with a minimum amount of input information, namely basic geometry which could be determined from simple design point calculations. Validation of the model was performed against compressor maps and geometries available in the literature. It was subsequently shown that with the blending of inlet, diffusion ratio and two-zone models, a centrifugal impeller model was constructed which agreed well over a wide range of rotational speeds and mass flow rates.
Advanced Weld Repair of Gas Turbine Hot Section Components
Authors: Arjakine Nikolai , Bruck Jerry , Gru¨ger Birgit , Seeger Dirk M. , Wilkenhoener Rolf
Published: August 2009

In the 21st century, generation of electrical power will play a critical role due to constantly rising global population and increasing energy demand. While energy resources such as oil, coal and natural gas are being rapidly exhausted, environmental concerns of global warming due to CO2 emissions are simultaneously imposing limits on consumption of these limited resources. Natural gas is one of the most efficient industrial fuels and therefore, over the last two decades, its use with stationary gas turbines has increased dramatically. New nickel based superalloys and advanced coating systems have been introduced to further advance the efficiency of such natural gas power generation equipment. While such new technologies increase the cost of newly manufactured parts, refurbishment of service exposed parts has become of increasing importance in the gas turbine business. For this reason, for example, modern joining methods have been developed to repair single crystal parts at significantly lower prices compared to manufacture of new parts. Repair of turbine hot gas path components is a proven service offered to customers by Siemens Power Generation (Siemens PG). Highly advanced brazing and welding processes are routinely applied to repair gas turbine parts. Particular concerns in the repair of such turbine parts made of cobalt and nickel based superalloys include high susceptibility to hot cracking during welding and post weld heat treating. Special technological subtleties must be applied for successful repair including use of ductile filler materials, welding methods with low heat input, hot box welding and complicated pre- and post-weld heat treatments to avoid weld cracking. This paper deals with some repair welding technologies currently used at Siemens PG.
Assessing of Hot Gas Parts Using Advanced Eddy Current Testing Methods
Authors: Jungbluth Matthias , Jonnalagadda Vinay , Baleine Erwan , Broddega˚rd Mattias , Wilkenho¨ner Rolf , Zombo Paul
Published: August 2009

The turbine section of state-of-the-art industrial gas turbines is exposed to the most severe conditions such as high temperatures, corrosive environments and high mechanical stresses for several tens of thousands of hours. To withstand these conditions, turbine blades and vanes have become the most sophisticated parts. This, together with advanced manufacturing technologies, strict quality requirements and maximum reliability demands, affects costs. Different design features have been realized in the past to meet the ambitious requirements, and are also under constant development. Blades and vanes made of superalloys with directionally-solidified or single-crystal structure are used to provide highest strengths at temperatures as near as possible to the hot gas temperature. The high integrity and conformity of the parts are required to realize the material potential. Different advanced diagnostic methods are applied to ensure these over time. Another way to increase the operating temperatures of gas turbines is the application of corrosion and thermal protection coatings for one or several rows of the blades and vanes. Deviations in the specified coating thickness tend to reduce the lifetime of such coatings significantly. Hence, the monitoring of this property during the manufacturing requires special nondestructive diagnostic measures. Service exposed parts, which need to be refurbished when the protective coatings are spent, offer a significant operation potential after refurbishment. To guarantee the design parameters during the next service interval, several nondestructive material evaluation methods are available for the necessary part property assessment. Multifrequency Eddy Current has proven itself as an appropriate NDE technique to accomplish the above diagnostic requirements. The paper will give an overview of results gained at Siemens with model based Eddy Current methods using measurement systems developed by Jentek Sensors Inc., USA, and CESI, Italy. Potential applications and limitations of the method also will be discussed.
Experimental Investigation of a Centrifugal Compressor Stage With Focus on the Flow in the Pipe Diffuser Supported by Particle Image Velocimetry (PIV) Measurements
Authors: Zachau Uwe , Buescher Carsten , Niehuis Reinhard , Hoenen Herwart , Wisler David C. , Moussa Zaher M.
Published: August 2009

Centrifugal compressor stages with pipe diffusers are considered to perform with high efficiency. Yet very little information on these kinds of diffusers is available to this day. Therefore, experimental investigations have been performed on a centrifugal compressor stage with a pipe diffuser. An extensive measurement series using various steady, unsteady and laser optical measurement techniques has been performed to detect the highly three dimensional diffuser flow and create a benchmark for further development steps. Whereas this paper presents the test rig and the results gathered under nominal conditions, in a follow-up paper the results of the parameter variation studies covering bleed variation, impeller tip clearance and impeller-diffuser misalignment are compared to the nominal baseline and evaluated with respect to the compressor stage performance. For the investigations performed under nominal conditions it was found that the diffuser flow separates on the pressure side in the first half of the pipe. In the last 30% of the pipe hardly any deceleration of the flow takes place. From this, special attention is drawn to the parameter variations regarding a first proposal for a diffuser design change, which consists in shortening the diffuser. Ongoing investigations cover this design proposal. Along with the results of the ongoing investigations, the numerical investigations accompanying the experimental work will also be presented in follow-up papers.
Hot Oxidation Studies for the Ti-6Al-4V Alloy at Environmental Atmosphere
Authors: Oliveira M. A. S. , Boschetti A. , Vilela M. S.
Published: August 2009

Surfaces of the Ti-6Al-4V alloy were submitted to a cleaning process using hot water and a cleaning agent aqueous solution used to clean up gas turbine compressors. Following the cleaning process, the Ti-6Al-4V surfaces were submitted to hot oxidation at temperatures of 400 and 800 °C, under environmental atmosphere, and different time t (t = 4, 8, 12, 16 and 20 hours). After the heat treatment, potentiodynamic tests were performed on the titanium alloy surfaces exposed to a sodium chloride containing aqueous solution. The morphology of the surfaces and of the cross-section of the oxidized alloy was investigated by Scanning Electron Microscopy (SEM), and the phases developed on the surfaces during the hot oxidation experiments were investigated by X-ray diffraction analyses (XRD). The corrosion process on the oxidized surfaces exposed to chloride containing solutions increased with the oxidizing temperature. Contrastingly, the corrosion of the Ti-6Al-4V alloy surfaces submitted to hot oxidation at 400 °C and exposed later to the chloride containing aqueous solution increased with time while the opposite was observed for those surfaces hot corroded at 800 °C. This difference in behavior was ascribed to the difference of phases developed on the titanium alloy surfaces during the hot oxidation process at 400 and 800 °C, respectively.
Development and Stability of Fish Assemblages after Lime Treatment
Authors: Appelberg Magnus , Degerman Erik
Published: August 2009

Long-term effects of limestone treatment on fish populations in acidified lakes in Sweden have been examined since 1983 to assess the development and stability of fish assemblages after lime treatment. In total, 77 lakes were sampled twice using standardized methods between 1983 and 1988. The lakes were limed 1–16 yr before the second sampling. Physical and chemical variables and the fish data were reduced using PCA ordination and the resulting relationships were analyzed using linear regression and ANOVA. Relationships between the fish assemblage characteristics and the environmental factors were highly dependent on the species composition of the assemblages. The number and diversity of fish species were correlated with both the extent of acidification and habitat diversity of the lakes. The importance of species interactions after lime treatment was suggested by a negative relationship between changes in the scores of community along the first component of the fish PCA and changes along two of the other species components between the two samplings. Despite a weak tendency towards reduced variability in species proportions as time passed since the first liming, the development of community stability, expressed as lack of change in species proportions, was insignificant.
Metabolic Organization of a Primitive Fish, the Bowfin (Amia calva)
Authors: Singer Thomas D. , Ballantyne James S.
Published: August 2009

Key enzymes in several metabolic pathways in five tissues were measured in primitive osteichthyan, the bowfin (Amia calva), the only living representative of the group of extant fishes most closely allied to the teleosts. Aspects of the metabolism of Amia differ from those of most teleosts studied. These differences include detectable levels of β-hydroxybutyrate dehydrogenase in all tissues, possibly a primitive metabolic feature of vertebrates, subsequently lost in most more advanced teleosts. Based on 3-hydroxyacyl CoA dehydrogenase and carnitine palmitoyltransferase activities, lipid metabolism in extrahepatic tissues of bowfin more closely resembles that of an elasmobranch rather than that of a teleost. The overall level of metabolism is lower than most teleosts as indicated by enzyme activities in red muscle and heart. Bowfin plasma nonesterified fatty acid concentrations are lower than most teleosts, but higher than those detected in any elasmobranch. These data suggest that the metabolic organization, especially lipid and ketone body metabolism, at least in part, reflects the evolutionary history of this group.
Temporal Variability in Antarctic Marine Ecosystems: Periodic Fluctuations in the Phocid Seals
Authors: Testa J. Ward , Oehlert Gary , Ainley David G. , Bengtson John L. , Siniff Donald B. , Laws Richard M. , Rounsevell David
Published: August 2009

Three species of seals around Antarctica have shown quasi-cyclic patterns in some aspect of their biology: the age structure of crabeater seals (Lobodon carcinophagus) around the Antarctic Peninsula has shown strong cohorts separated by 4- to 5-yr intervals; juvenile leopard seals (Hydrurga leptonyx) have appeared in unusually large numbers at Macquarie Island, also at 4- to 5-yr intervals; and Weddell seals (Leptonychotes weddellii) in McMurdo Sound have undergone fluctuations in reproductive rate every 4–6 yr. Complex demodulation was used to compare patterns among these three data sets and with the Southern Oscillation Index (SOI). All of the seal data sets showed evidence of cyclical behavior when demodulated at a period of 5 yr. The Weddell seals were generally in phase with the SOI since the Weddell series began in 1970. The leopard seals and SOI were in phase in the 1960's, but thereafter the SOI series led the leopard seal series by about one quarter of a cycle. The crabeater series was more complicated, but similarities with the other data sets also were seen. If these tentative observations are confirmed, they point to large-scale oceanographic variation, possibly related to the El Niño – Southern Oscillation (ENSO), as an important mechanism in Antarctic marine ecosystems.
Evaluation of Methods for Separation of Gulf of St. Lawrence Beaked Redfishes,Sebastes fasciatusandS.mentella: Malate Dehydrogenase Mobility Patterns Compared with Extrinsic Gasbladder Muscle Passages and Anal Fin Ray Counts
Authors: Rubec Peter J. , McGlade Jacquie M. , Trottier Bertin L. , Ferron André
Published: August 2009

Malate dehydrogenase (MDH) electrophoretic mobility patterns were used as a standard against which field methods involving anal fin ray counts (AFCs) and extrinsic gasbladder muscle (EGM) rib passage patterns were compared to separate the beaked redfish species, Sebastes fasciatus and S. mentella. The frequencies of MDH-A phenotypes were determined for 1125 beaked redfish examined from a winter survey in 1983 and 376 from a summer survey in 1984. Allele frequencies were calculated from the MDH-A phenotypic data for the winter survey. The low mobility of the A2phenotype was characteristic of 90% of S. fasciatus sampled at depths < 320 m in winter and at depths < 250 m in summer. The high-mobility A1and heterozygotic A1/A2phenotypes were prevalent in 95% of S. mentella sampled below these depths. The mobility patterns agreed with predominant AFCs ([Formula: see text] for S. fasciatu[Formula: see text] for S. mentella) for all stations in the deep and shallow zones. The MDH mobility patterns showed 93% agreement with EGM patterns for S. fasciatus but only 53% agreement for S. mentella. An overlap of AFCs, of main EGM patterns, and of tendon to vertebrae attachments and the variation from set to set in A1/A2heterozygotic phenotypes suggest that these species hybridize in the Gulf of St. Lawrence.
Prey-Size Relationships and Feeding Tactics of Primitive Stream-Dwelling Darters
Authors: Rakocinski Chet
Published: August 2009

Prey-size use and feeding tactics varied among three cooccurring darter species in the primitive subgenus Hadropterus (genus Percina). These darters span a wide range of body sizes, yet they all utilize the same lotic prey-size spectrum. An optimal-diet index (ODI) showed that small darters had more optimal diets than large darters. However, decelerating ODI curves showed that ontogenetic shifts occurred from number-maximizing to prey-size selective feeding tactics. Interspecific differences in feeding tactics, as characterized by differences in prey size, diet breadth, and numbers of prey, also were reflected by differences in slopes of ODI power curves. Percina nigrofasciata showed a relatively prey-size selective tactic; P. sciera showed a relatively number-maximizing tactic. In darters, prey-size selection corresponded with a broad diet and number maximizing corresponded with a narrow diet. When P. nigrofasciata were compared among four Black Creek sites, relatively optimal diets were found at two sites where large macroinvertebrates also were relatively abundant, as predicted from optimal foraging theory. However, only small differences in ODI values existed between two sites showing the greatest disparity in macroinvertebrate abundance. Prey size was an important diet characteristic related to the feeding tactics of particulate-feeding darters.
Electroporation of sperm to introduce foreign DNA into the genome of loach (Misgurnus anguillicaudatus)
Authors: Tsai H. J. , Tseng F. S. , Liao I. C.
Published: August 2009

An antifreeze protein gene promoter from ocean pout (Macrozoarces americanus) linked to a chinook salmon (Oncorhynchus tshawytscha) growth hormone cDNA (opAFPGHc) was introduced into loach (Misgurnus anguillicaudatus) sperm via electroporation under the following conditions: amplitude, 8 kV; burst time, 1.6 s; number of pulses; 28; pulse time, 120 μs; cycle, 6. Compared with the untreated sperm, the fertilization rate driven by the electroporated sperm was decreased slightly, with no significant effect on hatchability. The success rate of gene transfer was 50%. Genomic Southern blotting demonstrated that DNA from transgenic loach contained positive band(s) with higher (37.5%), the same, or lower molecular size as the transferred opAFPGHc fragment. There was a mosaic distribution of exogenous DNA in a wide variety of tissues analyzed. The average weight gain between the 14th and 161th day of the experimental group was 2.5-fold higher than those of the control and mock-treated groups. The body length distribution of the experimental group was rather widely scattered instead of being normally distributed.
Natural variability and the estimation of empirical relationships: a reassessment of regression methods
Authors: Prairie Yves T. , Bird David F. , Peters Robert H.
Published: August 2009

Ecologists often rely on empirically defined statistical relationships to infer how variables might be related. However, the usual method of estimating such relationships (ordinary least-squares (OLS)) is generally inappropriate because of the substantial natural variability of most ecological variables. Natural error variability in the regressor variable can artificially create a significant empirical trend where no underlying or structural relationship exists, or fail to reveal a true structural relationship. In multivariate relationships, natural variability in one variable can induce statistical significance in collinear variables even if they bear no structural relationship. We propose a simple new method, based on instrumental variables, to detect and quantify natural error variability in the regressor variables and to estimate the parameters of the structural relationship. We apply this method to two examples: (1) we show that the structural relationship between adenosine triphosphate concentration (total planktonic biomass) and chlorophyll concentration (autotrophic biomass) does not vary latitudinally in the Southern Ocean despite a significant increase in the OLS slope relating the two at more southerly stations and (2) we demonstrate that the significance of nitrogen in nutrient–chlorophyll relationships in lakes probably reflects natural variability in phosphorus concentration, and not the fertilizing effect of nitrogen.
Longitudinal and seasonal development of planktonio chlorophyllain the Rideau River, Ontario
Authors: Basu B. K. , Pick F. R.
Published: August 2009

Planktonic chlorophyll a (chl-a) concentrations in the Rideau River, Ontario showed longitudinal and seasonal variation and ranged from 2 to 19 μg∙L−1. Chlorophyll a concentrations in the river were not simply a reflection of the concentrations in the headwaters. On movement from the lentic headwaters into the lotic river waters there was usually a significant decrease in chl-a concentration. Downstream there were reaches of net increase in chl-a (sources), reaches of no change in concentration, and reaches of net decrease (sinks). Increases in concentration only occurred over reaches with retention times of 72 h or longer. No increases in chl-a concentration occurred over a reach with a retention time less than 50 h. Chlorophyll a concentration was not significantly correlated with discharge. Chlorophyll a concentration was positively related to total phosphorus concentration (R2 = 0.15, p = 0.016). About 50% of the variation in chl-a concentration could be accounted for by a combination of total phosphorus, nitrate, and soluble reactive phosphorus concentrations.
Episodic flow–duration analysis: a method of assessing toxic exposure of brook trout (Salvelinus fontinalis) to episodic increases in aluminum
Authors: DeWalle David R. , Swistock Bryan R. , Sharpe William E.
Published: August 2009

Episodic flow–duration curves were developed that summarize stream flow data by considering the duration of sustained flows at or above specified levels. These curves and relationships between dissolved aluminum concentrations and stream flow were combined for five Appalachian (Pennsylvania) streams to determine the frequency of occurrence of acutely toxic aluminum conditions for brook trout (Salvelinus fontinalis). Concentrations of total dissolved aluminum (AlTD) increased with stream flow in all streams, but reached a plateau or decreased during extreme high flows in some streams. AlTDwas dominated by inorganic monomeric species in all streams except Benner Run and Baldwin Creek. Episodic AlTDconcentrations and durations were compared with a toxicity curve developed using caged wild and hatchery-reared brook trout. Results predicted that lethal episodes occurred on Linn, Stone, and Roberts runs, but not on Benner Run and Baldwin Creek. With the exception of Stone Run, brook trout populations were largest in streams without predicted lethal episodes (Benner Run and Baldwin Creek) and were smallest in streams with predicted lethal episodes (Linn and Roberts runs). This analysis could be adapted for prediction of toxic conditions in streams for other pollutants where toxicity varies with both concentration and duration of exposure.
Concentrations of nucleic acids and protein as indices of nutritional status for recently emerged brook trout (Salvelinus fontinalis)
Authors: McLaughlin Robert L. , Ferguson Moira M. , Noakes David L. G.
Published: August 2009

We examined whether concentrations of nucleic acids and protein sampled from muscle tissue were useful indicators of nutritional status for recently emerged brook trout (Salvelinus fontinalis). Trout collected from the field were maintained in the laboratory under two food treatments: fed versus food deprived. Concentrations of RNA and DNA, and RNA/DNA ratio did not differ significantly between fed and food-deprived trout, but fed trout had higher concentrations of protein and were 20% heavier at a given fork length than food-deprived trout. Wild trout fed in the laboratory had lower concentrations of RNA, DNA, and protein, and lower RNA/DNA ratios than did trout in the field, but were significantly heavier for their fork length. Tissue concentrations of protein may provide an index of nutritional status for recently emerged brook trout while concentrations of nucleic acids apparently do not. It is important to ensure that concentrations of nucleic acids and protein reflect nutritional status adequately for the species and life stage of interest before using these indices to assess the condition of fish in the field.
Kinetics of excess (above background) copper and zinc in Hyalella azteca and their relationship to chronic toxicity
Authors: Borgmann U. , Norwood W. P.
Published: August 2009

One-week-long metal uptake experiments with Hyalella azteca are potentially a powerful tool for rapidly assessing the impact of copper or zinc in contaminated water samples. Copper and zinc concentrations in whole body Hyalella are independent of body size for both control and metal-exposed amphipods. Uptake rates are rapid for both metals, but copper concentrations in Hyalella during continuous exposure peak at about 1 week, then gradually decline back towards control levels at an apparent rate of 0.039 d−1. Hyalella can, therefore, control body copper concentrations during exposure to elevated copper, but only gradually and after long exposure periods. Depuration rates for copper and zinc (0.16 and 0.68 d−1 respectively) are approximately five times slower than the apparent depuration rates during uptake, assuming a simple diffusion model. Uptake at increasing water concentrations results in saturation for both metals with maximum accumulations of 3.6 μmol/g dry weight above background. A mathematical model including saturation kinetics satisfactorily explains the more rapid approach to equilibrium observed during uptake than during depuration. Significant chronic mortality occurred at metal exposures that resulted in predicted accumulations of 1.8 μmol Cu/g or 1.3 μmol Zn/g above background after 1 week of uptake.
Autoradiography of [3H]thymidine-labeled Chlamydia psittaci 6BC in mononuclear phagocytes
Authors: Martin Caroline , Wilt John C. , Kordová Nonna
Published: August 2009

Incorporation of tritiated [3H]thymidine by Chlamydia psittaci 6BC was achieved by growing the parasites in chick embryo yolk sac explants which were exposed to exogenous labeled thymidine. These labeled, purified chlamydiae were next observed by autoradiography within mouse peritoneal macrophages. The number of silver grains remained constant in the cytoplasm of macrophages throughout the developmental cycle of the parasite. The proliferation of labeled chlamydiae in macrophages was confirmed by Giemsa staining and immunofluorescence. Chlamydiae have never been successfully labeled with thymidine in earlier studies when assayed in cultured mammalian fibroblasts. It is suggested that a critical factor in the successful incorporation of thymidine in chlamydiae may be the host–parasite system used.
Improved techniques for the preparation of bacterial lipopolysaccharides
Authors: Johnson K. G. , Perry M. B.
Published: August 2009

Lipopolysaccharides were prepared from six organisms by the use of two cell-disruption procedures before conventional phenol–water extraction. Disruption of cells by grinding with glass beads or by digestion with hen egg white lysozyme before phenol extraction facilitated rapid purification and greater yields of lipopolysaccharide. Pretreatment of cells with lysozyme in the presence of ethylenediaminetetraacetic acid was the most efficient method in terms of lipopolysaccharide yield and ease of preparation. Increase in lipopolysaccharide yield achieved by use of the lysozyme method, compared with the conventional phenol extraction, varied from 1.7- to 12.4-fold. Preparations were designated as pure according to several criteria and were judged not to have undergone changes as a result of prephenol extraction procedures.
ON SEGMENTATION OF TOUCHING CHARACTERS AND OVERLAPPING LINES IN DEGRADED PRINTED GURMUKHI SCRIPT
Authors: JINDAL MANISH KUMAR , LEHAL GURPREET SINGH , SHARMA RAJENDRA KUMAR
Published: August 2009

Character segmentation plays a very important role in a text recognition system. The simple technique of using inter-character gap for segmentation is useful for fine printed documents, but this technique fails to give satisfactory results if the input text contains touching characters. In this paper, we have proposed two algorithms to segment touching characters, and one algorithm to segment overlapping lines in degraded printed Gurmukhi document. Various categories of touching characters in different zones, along with their solutions, have been proposed. The solution methodology extensively uses the structural properties of Gurmukhi script. The algorithm proposed for segmenting horizontally overlapping lines uses a heuristics based upon the height of a character. The problem of multiple horizontally overlapping lines may occur in a number of situations such as printed newspapers, old magazines and books etc. Similarity among Indian scripts allows us to use these algorithms for solving the segmentation problems in other Indian languages also.