bluuebunny/crossref_metadata_2025 huggingface dataset:
Motor primitives and synergies in the spinal cord and after injury—the current state of play
Authors: Giszter Simon F. , Hart Corey B.
Published: March 2013

Modular pattern generator elements, also known as burst synergies or motor primitives, have become a useful and important way of describing motor behavior, albeit controversial. It is suggested that these synergy elements may constitute part of the pattern‐shaping layers of a McCrea/Rybak two‐layer pattern generator, as well as being used in other ways in the spinal cord. The data supporting modular synergies range across species including humans and encompass motor pattern analyses and neural recordings. Recently, synergy persistence and changes following clinical trauma have been presented. These new data underscore the importance of understanding the modular structure of motor behaviors and the underlying circuitry to best provide principled therapies and to understand phenomena reported in the clinic. We discuss the evidence and different viewpoints on modularity, the neural underpinnings identified thus far, and possible critical issues for the future of this area.
Molecular, genetic, cellular, and network functions in the spinal cord and brainstem
Authors: Stein Paul S.G.
Published: March 2013

Studies of the model systems of spinal cord and brainstem reveal molecular, genetic, and cellular mechanisms that are critical for network and behavioral functions in the nervous system. Recent experiments establish the importance of neurogenetics in revealing cellular and network properties. Breakthroughs that utilize direct visualization of neuronal activity and network structure provide new insights. Major discoveries of plasticity in the spinal cord and brainstem contribute to basic neuroscience and, in addition, have promising therapeutic implications.
Principles of interneuron development learned from Renshaw cells and the motoneuron recurrent inhibitory circuit
Authors: Alvarez Francisco J. , Benito‐Gonzalez Ana , Siembab Valerie C.
Published: March 2013

Renshaw cells provide a convenient model to study spinal circuit development during the emergence of motor behaviors with the goal of capturing principles of interneuron specification and circuit construction. This work is facilitated by a long history of research that generated essential knowledge about the characteristics that define Renshaw cells and the recurrent inhibitory circuit they form with motoneurons. In this review, we summarize recent data on the specification of Renshaw cells and their connections. A major insight from these studies is that the basic Renshaw cell phenotype is specified before circuit assembly, a result of their early neurogenesis and migration. Connectivity is later added, constrained by their placement in the spinal cord. Finally, different rates of synapse proliferation alter the relative weights of different inputs on postnatal Renshaw cells. Based on this work some general principles on the integration of spinal interneurons in developing motor circuits are derived.
Maternal adiposity as an independent risk factor for pre‐eclampsia: a meta‐analysis of prospective cohort studies
Authors: Wang Z. , Wang P. , Liu H. , He X. , Zhang J. , Yan H. , Xu D. , Wang B.
Published: March 2013

Studies investigating the association between maternal adiposity and risk of pre‐eclampsia showed contradictory results. Therefore, we performed a meta‐analysis of prospective cohort studies to estimate the effect of maternal adiposity on pre‐eclampsia. We reviewed 1,286 abstracts and finally included 29 prospective cohort studies with 1,980,761 participants and 67,075 pre‐eclampsia events. We pooled data with a random‐effects model, and obtained risk estimates for five predetermined bodyweight groups: low, normal‐weight (reference), overweight, obese and severely obese. In the cohort studies that unadjusted for pre‐eclampsia risk factors, the pooled unadjusted relative risks (RR) with 95% confidence intervals (95%CI) for pre‐eclampsia of overweight, obese and severely obese women were 1.58 (95% CI 1.44–1.72, P < 0.001), 2.68 (95% CI 2.39–3.01, P < 0.001) and 3.12 (95% CI 2.24–4.36, P < 0.001), respectively. In those cohorts that adjusted for pre‐eclampsia risk factors, the pooled unadjusted RRs for pre‐eclampsia of overweight, obese and severely obese women were 1.70 (95% CI 1.60–1.81, P < 0.001), 2.93 (95% CI 2.58–3.33, P < 0.001) and 4.14 (95% CI 3.61–4.75, P < 0.001), respectively. Sensitivity analysis showed maternal adiposity was associated with increased risk of pre‐eclampsia in both nulliparous and multiparas women. In conclusion, overweight or obese pregnant women have a substantially increased risk of pre‐eclampsia, and maternal adiposity is an independent risk factor of pre‐eclampsia.
Modelling the impact of spherical aberration on accommodation
Authors: Thibos Larry N , Bradley Arthur , López‐Gil Norberto
Published: March 2013

Purpose

To understand how primary and secondary spherical aberrations affect focusing of the retinal image and the measurement of refractive state in the accommodating eye.

Methods

A computational eye model was constructed from published anatomical dimensions of the eye's refractive elements for a range of accommodative states. Two strategies for controlling accommodation were implemented, one in which paraxial rays are always perfectly focused and the other in which paraxial accommodative lag grew larger as target vergence increased. Multiple configurations of the model were achieved by selecting various combinations of pupil size and aberration structure. Refractive state was defined as optimum target vergence for maximizing retinal image quality according to several scalar metrics.

Results

When accommodation optimally focuses paraxial rays, retinal image quality is sub‐optimal for metrics of image quality sensitive to non‐paraxial rays. This loss of image quality can be recovered by optimizing target vergence computationally, which indicates the presence of real accommodative error according to the non‐paraxial metric even though the eye is accurately focused paraxially. However, such errors are spurious if non‐paraxial refractive state is misinterpreted as paraxial refractive state. Accommodative errors may indicate lag or lead, but in general the slope of the stimulus‐response function is less than 1 for non‐paraxial measures of image quality. These results depend strongly on pupil size and its variation due to accommodative miosis.

Conclusions

spurious accommodative errors can appear when the eye focuses the retinal image optimally according to one metric of image quality (e.g. paraxial) while ocular refractive state is measured by another (e.g. non‐paraxial). Spurious errors are small compared to real accommodative lag for small, photopic pupils but can be of the same order of magnitude as real lag for large, mesopic pupils.
Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers
Authors: CANO F. JAVIER , SÁNCHEZ‐GÓMEZ DAVID , RODRÍGUEZ‐CALCERRADA JESÚS , WARREN CHARLES R. , GIL LUIS , ARANDA ISMAEL
Published: March 2013

In recent years, many studies have focused on the limiting role of mesophyll conductance (gm) to photosynthesis (An) under water stress, but no studies have examined the effect of drought on gm through the forest canopy. We investigated limitations to An on leaves at different heights in a mixed adult stand of sessile oak (Quercus petraea) and beech (Fagus sylvatica) trees during a moderately dry summer. Moderate drought decreased An of top and lowest beech canopy leaves much more than in leaves located in the mid canopy; whereas in oak, An of the lower canopy was decreased more than in sunlit leaves. The decrease of An was probably not due to leaf‐level biochemistry given that VCmax was generally unaffected by drought. The reduction in An was instead associated with reduction in stomatal and mesophyll conductances. Drought‐induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought‐induced increases in mesophyll limitations were largest in leaves from the lowest canopy. Sensitivity analysis highlighted the need to decompose the canopy into different leaf layers and to incorporate the limitation imposed by gm when assessing the impact of drought on the gas exchange of tree canopies.
Outcome of heart transplantation in pediatric cancer survivors
Authors: Shah Nishant , Aggarwal Sanjeev , L'Ecuyer Thomas
Published: March 2013

The aim of this study is to evaluate the outcome of heart transplantation in children surviving malignancies. Pediatric heart transplant recipients were identified using the UNOS database. Follow‐up data including survival and rate of malignancy were analyzed. A total of 7169 children received heart transplants between 1987 and 2011. Of these, 107 (1.5%) survived previous malignancy treatment (group I) and 7062 (98.5%) did not have prior malignancy (group II). Survival after transplant was 92.5%, 90.6%, 80.3%, and 65% at three months, one, five, and 10 yr in group I, similar to the rate in group II (90.1%, 84.4%, 73.8%, and 57.7%). Survival after transplantation was similar between group I and children who underwent OHT secondary to cardiomyopathy in group II. The rate of post‐OHT malignancy in group I was higher than that in group II (14/107(13%) vs. 386/7062 (5.4%), p = 0.001). Children who developed malignancy in group I had similar survival as children who developed malignancy in group II. Post‐transplant survival is similar in children with and without pretransplant malignancy in spite of higher rate of malignancy in children with pretransplant malignancy. OHT appears to be a reasonable treatment option in children who develop end‐stage heart disease after malignancy treatment.
What's in a Name? The Covenant of Mayors as Transnational Environmental Regulation
Authors: Heyvaert Veerle
Published: March 2013

This article asks whether the Covenant of Mayors – a transnational network that aims to reduce CO2 emissions in European towns and cities – amounts to transnational environmental regulation. It answers in the affirmative. The relevance of treating the Covenant of Mayors as transnational environmental regulation is that this triggers qualitative expectations about how decision‐making power will be wielded within the network. The article indicates that the Covenant is likely to clear some of these qualitative hurdles, but may struggle with others. This calls for further deliberation on how to bolster the legitimacy of transnational environmental regulation without forsaking its flexibility and innovative drive. Considering that the outlook for the swift, successful adoption of a global, binding regulatory regime for climate change is bleak, the world will likely remain dependent on alternative, transnational initiatives as drivers for change. The ramifications of this debate therefore considerably exceed the scope of the Covenant of Mayors itself.
Shared Accountability of the European Union and its Member States in the Climate Change Regime
Authors: Tabau Anne‐Sophie
Published: March 2013

This article addresses the distribution of accountability between the European Union (EU) and its Member States under the current and future climate regime. Belonging to a field of shared competence between the EU and its Member States, the climate regime is characterized by ‘mixed agreements’, not distinguishing between the obligations of the EU and its Member States. This raises the question of how to determine who is accountable in case of non‐compliance. Under the current regime, there is a joint and proportional accountability rule regarding the European common emission reduction target. This rule is well suited to the nature of the EU, and should therefore be maintained in the next climate agreement. For other commitments, third parties, the Secretariat of the Climate Change Convention and the Kyoto Protocol Compliance Committee enjoy a margin of discretion to evaluate whether it is pragmatic to address non‐compliance with regard to only the Member State concerned or to involve the EU in the process. This approach, favouring a return to compliance, also appears adapted to the EU. Indeed, an ad hoc intra‐European mechanism allows for the identification of the actor actually accountable. To avoid holding the EU as a whole accountable while the entity actually accountable is a Member State or the EU, some intra‐European actions for recovery are available to the EU, its Member States and even private persons.
A Conceptual and Legal Perspective on the Green Economy
Authors: Morgera Elisa , Savaresi Annalisa
Published: March 2013

The 2012 United Nations Conference on Sustainable Development had as one of its two main themes ‘a green economy in the context of sustainable development and poverty eradication’. The Conference did not agree upon a definition of ‘green economy’ and limited itself to ‘[encouraging] each country to consider the implementation of green economy policies’ as one of the different approaches available to achieve sustainable development. Nevertheless, its outcome document provides a host of indications about the challenges and opportunities to achieve sustainable development through the green economy. This article offers a conceptual and legal perspective on the green economy by investigating the evolution of the related policy debate and focusing on whether the text on the green economy adopted at Rio+20 provides new insights on the implementation of sustainable development, notably in relation to environmental integration, intra‐generational equity, human rights and corporate accountability.
Technology and Innovation for a Green Economy
Authors: Eaton Derek
Published: March 2013

This article discusses the role that innovation plays in the transition to a green economy, with special attention paid to the importance of diffusion and transfer of technologies. The article first describes the origins and conceptual foundations of a transition to a green economy, concentrating on the initiative launched by the United Nations Environment Programme, and leading to the United Nations Conference on Sustainable Development in Rio de Janeiro in June 2012 (Rio+20). The article then reviews the critical role of innovation in the reconfiguration of the economy's capital stock, leading to a discussion of the roles of both innovation and environmental policy in promoting such technological change. It next discusses the channels for international transfer of technologies and their relationship to the international policy architecture, and proposes that international discussions concerning technology transfer, particularly those related to environmental technologies, have suffered from a lack of coherence in policy positions, based probably on a fundamental misunderstanding of the economic nature of these processes.
The Rise and Fall of Sustainable Development
Authors: Viñuales Jorge E.
Published: March 2013

Sustainable development is turning brownish. Too many disparate initiatives are being conducted under its banner. The concept of ‘sustainable development’ no longer provides an adequate umbrella for the main challenge currently faced by global environmental governance – namely implementation. Its very strengths are turning into fatal weaknesses. Vague enough to bring all States and other stakeholders to the negotiating table, the concept of ‘sustainable development’ was very successful in managing the political collision between ‘development’ and ‘environment’ throughout the 1980s and the 1990s. It was a formidable tool to find balance as well as for normative development. But it is inadequate to navigate the implementation phase. This article introduces an alternative model, based on four strategic priorities (participation, differentiation, decarbonization, and innovation and technology diffusion). It maps different levels at which these priorities could be pursued in order to make global environmental governance more effective. The article is not against the concept of ‘sustainable development’ as a worthy ‘fight’. It is about the need to use another ‘weapon’ to spearhead efforts to meet the challenge of implementation.
China, Minerals Export, Raw and Rare Earth Materials: A Perfect Storm for World Trade Organization Dispute Settlement
Authors: Van Calster Geert
Published: March 2013

In China – Raw Materials, the World Trade Organization (WTO) Panel and Appellate body firmly restrict the application of General Agreement on Tariffs and Trade Article XX's ‘conservation of exhaustible natural resources’ to ecological considerations. This has an immediate impact on China's policy with respect to raw materials (including rare earth elements). It also impacts on any future challenge of the Organization of the Petroleum Exporting Countries under the WTO.
Impact on life after a major bus crash – a qualitative study of survivors' experiences
Authors: Doohan Isabelle , Saveman Britt‐Inger
Published: March 2013

Background

Crashes occur regularly throughout the world and can result in multiple fatalities and many injuries. Research into how survivors experience a crash is very limited.

Aim

To describe and analyse the nonphysical consequences of a multifatality bus crash in Sweden and the subsequent effect on the surviving passengers' lives.

Method

The participants were all (n = 56) of the survivors of a major bus crash. The passengers were interviewed approximately one month after the bus crash. The interviews were analysed using a qualitative content analysis.

Results

Prior to the arrival of rescue personnel at the crash site, helpfulness emerged among the passengers. Further, the crash generated an impact on the surviving passengers' lives from a short‐term perspective. The passengers displayed a diverse need for crisis support; informal support from family and friends was essential for the early healing process. Sleep difficulties and a change in travel routines were the most common consequences. Lastly, passengers sought closure in order to move on with their lives.

Conclusion

The passengers' reactions to and behaviour following a crash offer an insight into the, relatively unexplored, interaction between people experiencing a major road traffic crash. It is necessary to have a flexible crisis support system, and the vital role of family support ought to be upgraded.
Identification of a new HLA‐B*46 allele, B*46:37, in a Chinese individual
Authors: Zhou X.‐Y. , Hei A.‐L. , Cai J.‐P.
Published: March 2013

A novel allele B*46:37 was identified in a Chinese individual.
Geomorphic expression of the southern Central Andes forebulge (37°S, Argentina)
Authors: Nivière Bertrand , Messager Grégoire , Carretier Sébastien , Lacan Pierre
Published: March 2013

We present a geomorphologic analysis of an east‐west transect located east of the southern Andes of Argentina (~37°S). We observe a succession of zones that underwent erosion and deposition during the Pleistocene. If the proximal Andean foothills are incised, a proximal depozone receives sediments feeding the megafan of the Rio Colorado on the Chadileuvú plain. More distally, the abandoned palaeo‐valleys and bending of the valley floors reflect a localized uplift. Further to the east, another depozone corresponds to the Pampa Deprimida lowland. This pattern is consistent with the presence of a classical flexural geometry of the lithosphere. The distal uplift of the foreland corresponds in terms of location, length (150 km) and amplitude (240 m) to the Andean forebulge modelled by a geophysical approach. In this study, we identify the morphological imprint of this bulge and show its effect on the fluvial activity.
Modelling population dynamics of Sinapis arvensis in organically grown spring wheat production systems
Authors: Kolb L N , Gallandt E R
Published: March 2013

Although we know that alterations in crop density, crop spatial pattern and inclusion of more selective weed control can improve weed suppression for organic growers, it is unknown whether these result in changes to the weed seedbank that increase cropping system profitability over time. Data collected from field trials conducted in 2009 and 2010 in Maine, USA, comparing regional grower practices (Standard) with management that aimed to (i) facilitate better physical weed control through the use of wide row spacing and inter‐row cultivation (Wide) or (ii) enhance crop–weed competition through increased seeding rate and narrow inter‐row spacing (Narrow HD), were used to construct a matrix population model with an economic sub‐model. Using field measurements of grain yield and weed survival and fecundity, we investigated the lasting implications of employing alternative organic spring wheat (Triticum aestivum) production practices on Sinapis arvensis population dynamics. In most scenarios, the model indicated that regional production practices were not sufficient to prevent an increase in the weed seedbank, even with excellent weed control. The two alternative methods, on the other hand, were able to limit weed population growth when initial densities were low or cultivation efficacy was >80%. Due to higher seed costs in the Narrow HD system, net returns were still lower after 10 years of simulation in this system compared with wide rows with cultivation, despite a lower weed seedbank.
Detection of mitochondrial depolarization/recovery during ischaemia–reperfusion using spectral properties of confocally recorded TMRM fluorescence
Authors: Venable Paul W. , Taylor Tyson G. , Sciuto Katie J. , Zhao Jerry , Shibayama Junko , Warren Mark , Spitzer Kenneth W. , Zaitsev Alexey V.
Published: March 2013

Key points

Mitochondrial inner membrane potential (ΔΨm) collapse during myocardial ischaemia is one of the key events determining the physiological consequences of ischaemic attack in terms of post‐ischaemic arrhythmias and cell survival.

Timing and pattern of ΔΨm collapse during ischaemia remain controversial, in part due to difficulties in interpreting the fluorescence of potentiometric cationic probes commonly used for assessment of ΔΨm in cellular and multicellular experimental models.

This manuscript presents a new method for monitoring ΔΨm in whole hearts based on the regular arrangement of mitochondria in cardiac myocytes, thus permitting detection of ΔΨm collapse using spectral analysis of fluorescence.

The proposed method will help to ascertain the role of mitochondrial function in acute cardiovascular conditions, such as acute myocardial infarction or sudden cardiac arrest.

Abstract  Timing and pattern of mitochondrial potential (ΔΨm) depolarization during no‐flow ischaemia–reperfusion (I–R) remain controversial, at least in part due to difficulties in interpreting the changes in the fluorescence of ΔΨm‐sensitive dyes such as TMRM. The objective of this study was to develop a new approach for interpreting confocal TMRM signals during I–R based on spatial periodicity of mitochondrial packaging in ventricular cardiomyocytes. TMRM fluorescence (FTMRM) was recorded from Langendorff‐perfused rabbit hearts immobilized with blebbistatin using either a confocal microscope or an optical mapping system. The hearts were studied under normal conditions, during mitochondrial uncoupling using the protonophore FCCP, and during I–R. Confocal images of FTMRM were subjected to spatial Fourier transform which revealed distinct peaks at a spatial frequency of ∼2 μm−1. The area under the peak (MPA) progressively decreased upon application of increasing concentrations of FCCP (0.3–20 μm), becoming undetectable at 5–20 μm FCCP. During ischaemia, a dramatic decrease in MPA, reaching the low/undetectable level comparable to that induced by 5–20 μm FCCP, was observed between 27 and 69 min of ischaemia. Upon reperfusion, a heterogeneous MPA recovery was observed, but not a de novo MPA decrease. Both confocal and wide‐field imaging registered a consistent decrease in spatially averaged FTMRM in the presence of 5 μm FCCP, but no consistent change in this parameter during I–R. We conclude that MPA derived from confocal images provides a sensitive and specific indicator of significant mitochondrial depolarization or recovery during I–R. In contrast, spatially averaged FTMRM is not a reliable indicator of ΔΨm changes during I–R.
In vivo cholinergic modulation of the cellular properties of medial entorhinal cortex neurons
Authors: Tsuno Yusuke , Schultheiss Nathan W. , Hasselmo Michael E.
Published: March 2013

Key points

Medial entorhinal cortex neurons show special intrinsic properties in vitro, which might be important for contributing to functional cell properties, such as grid cell firing.

Both intrinsic properties in slices of medial entorhinal cortex and grid cell activity in vivo are affected by cholinergic activation, but the relationships between these effects are unknown.

Using intracellular recording, we show that intrinsic properties including sag amplitude, sag time constant and resonance frequency are affected by cholinergic activation in vivo, and these results are consistent with in vitro studies.

Furthermore, we show that the relationship between firing frequency and input current is also changed by cholinergic activation in our in vivo recordings.

These results suggest the importance of cholinergic influences on the intrinsic properties of medial entorhinal neurons, and help us understand how this influence contributes to mechanisms of spatial memory and the cause of memory impairment.

Abstract  Extensive in vitro data and modeling studies suggest that intrinsic properties of medial entorhinal cortex (MEC) neurons contribute to the spiking behaviour of functional cell types of MEC neurons, such as grid cells, recorded in behaving animals. It remains unclear, however, how intrinsic properties of MEC neurons influence cellular dynamics in intact networks in vivo. In order to begin to bridge the gap between electrophysiological data sets from brain slices and behaving animals, in the present study we performed intracellular recordings using sharp electrodes in urethane‐anaesthetized rats to elucidate the cellular dynamics of MEC neurons in vivo. We focused on the h‐current‐dependent sag potential during hyperpolarizing current steps, subthreshold resonance in response to oscillatory frequency sweeps (chirp stimuli), persistent spiking in response to brief depolarizing inputs and the relationship between firing frequency and input (f–I curve), each of which is sensitive to cholinergic modulation in vitro. Consistent with data from in vitro studies, cholinergic activation by systemic application of the acetylcholinesterase inhibitor, physostigmine, resulted in decreased sag amplitude, increased sag time constant and a decrease of the peak resonance frequency. The f–I curve was also modulated by physostigmine in many neurons, but persistent spiking was not observed in any of our recordings, even when picrotoxin, a GABAA blocker, was included in the internal solution of the recording pipette to reduce possible effects of network inhibition. These results suggest that intrinsic oscillatory and rate‐coding mechanisms, but not intrinsic bistability, are significantly modulated by acetylcholine in the intact entorhinal network.
The Aerothermal Performance of a Cooled Winglet Tip in a High Pressure Turbine Cascade
Authors: Zhou Chao , Hodson Howard , Tibbott Ian , Stokes Mark
Published: March 2013

The aerothermal performance of a winglet tip with cooling holes on the tip and on the blade surface near the tip is reported in this paper. The investigation was based on a high pressure turbine cascade. Experimental and numerical methods were used. The effects of the coolant mass flow rate are also studied. Because the coolant injection partially blocks the tip leakage flow, more passage flow is turned by the blade. As a result, the coolant injection on the winglet tip reduces the deviation of the flow downstream of the cascade due to the tip leakage flow. However, the tip leakage loss increases slightly with the coolant mass flow ratio. Both the computational fluid dynamics tools and experiments using the Amonia–Diazo technique were used to determine the cooling effectiveness. On the blade pressure side surface, low cooling effectiveness appears around the holes due to the lack of the coolant from the cooling hole or the lift-off of the coolant from the blade surface when the coolant mass flow is high. The cooling effectiveness on the winglet tip is a combined effect of the coolant ejected from all the holes. On the top of the winglet tip, the average cooling effectiveness increases and the heat load decreases with increasing coolant mass flow. Due to its large area, the cooled winglet tip has a higher heat load than an uncooled flat tip at engine representative coolant mass flow ratio. Nevertheless, the heat flux rate per unit area of the winglet is much lower than that of an uncooled flat tip. The cycle analysis is carried out and the effects of relative tip-to-casing endwall motion are address.
A Novel Measuring Technique Utilizing Temperature Sensitive Paint—Measurement Procedure, Validation, Application, and Comparison With Infrared Thermography
Authors: Lorenz M. , Horbach T. , Schulz A. , Bauer H.-J.
Published: March 2013

A novel method for surface temperature measurement using temperature sensitive paint (TSP) is presented. Precalibration of the TSP is shown and a semi in situ calibration technique using thermocouples is provided for high accuracy measurement. The method presented is applied to a film cooling experiment with a maximum surface temperature of 430 K and compared to highly reliable infrared thermography measurements that serve as benchmark results. The in situ calibration technique shows a maximum deviation of 0.5 K from the thermocouple readings. The comparison of laterally averaged temperature distributions of TSP and infrared measurement shows excellent agreement.
Large-Eddy Simulation With Zonal Near Wall Treatment of Flow and Heat Transfer in a Ribbed Duct for the Internal Cooling of Turbine Blades
Authors: Patil Sunil , Tafti Danesh
Published: March 2013

Large eddy simulations of flow and heat transfer in a square ribbed duct with rib height to hydraulic diameter of 0.1 and 0.05 and rib pitch to rib height ratio of 10 and 20 are carried out with the near wall region being modeled with a zonal two layer model. A novel formulation is used for solving the turbulent boundary layer equation for the effective tangential velocity in a generalized co-ordinate system in the near wall zonal treatment. A methodology to model the heat transfer in the zonal near wall layer in the large eddy simulations (LES) framework is presented. This general approach is explained for both Dirichlet and Neumann wall boundary conditions. Reynolds numbers of 20,000 and 60,000 are investigated. Predictions with wall modeled LES are compared with the hydrodynamic and heat transfer experimental data of (Rau et al. 1998, “The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel,”ASME J. Turbomach., 120, pp. 368–375). and (Han et al. 1986, “Measurement of Heat Transfer and Pressure Drop in Rectangular Channels With Turbulence Promoters,” NASA Report No. 4015), and wall resolved LES data of Tafti (Tafti, 2004, “Evaluating the Role of Subgrid Stress Modeling in a Ribbed Duct for the Internal Cooling of Turbine Blades,” Int. J. Heat Fluid Flow 26, pp. 92–104). Friction factor, heat transfer coefficient, mean flow as well as turbulent statistics match available data closely with very good accuracy. Wall modeled LES at high Reynolds numbers as presented in this paper reduces the overall computational complexity by factors of 60–140 compared to resolved LES, without any significant loss in accuracy.
An Experimental Study on Aerodynamic Performance of Turbine Nozzle Guide Vanes With Trailing-Edge Span-Wise Ejection
Authors: Aminossadati S. M. , Mee D. J.
Published: March 2013

The present experimental study is to examine the influence of trailing-edge coolant ejection with the span-wise inclination on the aerodynamic loss of turbine nozzle guide vanes. This study uses a cascade of five vanes located in the test section of a low-speed wind tunnel. The vanes have the profile of high-pressure nozzle guide vanes, and the central vane is equipped with the internal cooling and the trailing-edge coolant ejection. The coolant is ejected through trailing-edge slots that are inclined in the span-wise direction at angles varying from 0 deg to 45 deg in 15 deg increments. The results indicate an optimum ejection rate, at which the aerodynamic loss is minimum. There is a little variation in loss as the span-wise inclination is varied when the ratio of coolant to mainstream gas mass flow rate is less than 1.5%. For higher coolant flow rates, however, the loss increases with increases in the span-wise ejection angle.
Mistuning Identification of Integrally Bladed Disks With Cascaded Optimization and Neural Networks
Authors: Yumer Mehmet Ersin , Cigeroglu Ender , Özgüven H. Nevzat
Published: March 2013

Mistuning affects forced response of bladed disks drastically; therefore, its identification plays an essential role in the forced response analysis of bladed disk assemblies. Forced response analysis of mistuned bladed disk assemblies has drawn wide attention of researchers but there are a very limited number of studies dealing with identification of mistuning, especially if the component under consideration is an integrally bladed disk (blisk). This paper presents two new methods to identify mistuning of a bladed disk from the assembly modes via utilizing cascaded optimization and neural networks. It is assumed that a tuned mathematical model of the blisk under consideration is readily available, which is always the case for today’s realistic bladed disk assemblies. In the first method, a data set of selected mode shapes and natural frequencies is created by a number of simulations performed by mistuning the tuned mathematical model randomly. A neural network created by considering the number of modes, is then trained with this data set. Upon training the network, it is used to identify mistuning of the rotor from measured data. The second method further improves the first one by using it as a starting point of an optimization routine and carries out an optimization to identify mistuning. To carry out identification analysis by means of the proposed methods, there are no limitations on the number of modes or natural frequencies to be used. Thus, unlike existing mistuning identification methods they are suitable for incomplete data as well. Moreover, since system modes are used rather than blade alone counterparts, the techniques are ready to be used for analysis of blisks. Case studies are performed to demonstrate the capabilities of the new methods by using two different mathematical models to create training data sets a lumped-parameter model and a relatively realistic reduced order model. Throughout the case studies, the effects of using incomplete mode families and random errors in assembly modes are investigated. The results show that, the proposed method utilizing cascaded optimization and neural networks can identify mistuning parameters of a realistic blisk system with an exceptional accuracy even in the presence of incomplete and noisy test data.
Contrarotating Open Rotor Operation for Improved Aerodynamics and Noise at Takeoff
Authors: Zachariadis Alexios , Hall Cesare , Parry Anthony B.
Published: March 2013

The contrarotating open rotor is, once again, being considered as an alternative to the advanced turbofan to address the growing pressure to cut aviation fuel consumption and carbon dioxide emissions. One of the key challenges is meeting community noise targets at takeoff. Previous open rotor designs are subject to poor efficiency at takeoff due to the presence of large regions of separated flow on the blades as a result of the high incidence needed to achieve the required thrust. This is a consequence of the fixed rotor rotational speed constraint typical of variable pitch propellers. Within the study described in this paper, an improved operation is proposed to improve performance and reduce rotor-rotor interaction noise at takeoff. Three-dimensional computational fluid dynamics (CFD) calculations have been performed on an open rotor rig at a range of takeoff operating conditions. These have been complemented by analytical tone noise predictions to quantify the noise benefits of the approach. The results presented show that for a given thrust, a combination of reduced rotor pitch and increased rotor rotational speed can be used to reduce the incidence onto the front rotor blades. This is shown to eliminate regions of flow separation, reduce the front rotor tip loss and reduce the downstream stream tube contraction. The wakes from the front rotor are also made wider with lower velocity defect, which is found to lead to reduced interaction tone noise. Unfortunately, the necessary increase in blade speed leads to higher relative Mach numbers, which can increase rotor alone noise. In summary, the combined CFD and aeroacoustic analysis in this paper shows how careful operation of an open rotor at takeoff, with moderate levels of repitch and speed increase, can lead to improved front rotor efficiency as well as appreciably lower overall noise across all directivities.
Overall Effectiveness for a Film Cooled Turbine Blade Leading Edge With Varying Hole Pitch
Authors: Dyson Thomas E. , Bogard David G. , Piggush Justin D. , Kohli Atul
Published: March 2013

Overall effectiveness, φ, for a simulated turbine blade leading edge was experimentally measured using a model constructed with a relatively high conductivity material selected so that the Biot number of the model matched engine conditions. The model incorporated three rows of cylindrical holes with the center row positioned on the stagnation line. Internally the model used an impingement cooling configuration. Overall effectiveness was measured for pitch variation from 7.6d to 11.6d for blowing ratios ranging from 0.5 to 3.0, and angle of attack from −7.7 deg to + 7.7 deg. Performance was evaluated for operation with a constant overall mass flow rate of coolant. Consequently when increasing the pitch, the blowing ratio was increased proportionally. The increased blowing ratio resulted in increased impingement cooling internally and increased convective cooling through the holes. The increased internal and convective cooling compensated, to a degree, for the decreased coolant coverage with increased pitch. Performance was evaluated in terms of laterally averaged φ, but also in terms of the minimum φ. The minimum φ evaluation revealed localized hot spots which are arguably more critical to turbine blade durability than the laterally averaged results. For small increases in pitch (from p/d = 7.6 to 9.6) there was only a small decrease in performance, but at p/d = 11.6 a significant reduction was observed.
Differential Equation Specification of Integral Turbulence Length Scales
Authors: Jefferson-Loveday Richard J. , Tucker Paul G. , Northall John D. , Nagabhushana Rao V.
Published: March 2013

A Hamilton–Jacobi differential equation is used to naturally and smoothly (via Dirichlet boundary conditions) set turbulence length scales in separated flow regions based on traditional expected length scales. Such zones occur for example in rim-seals. The approach is investigated using two test cases, flow over a cylinder at a Reynolds number of 140,000 and flow over a rectangular cavity at a Reynolds number of 50,000. The Nee–Kovasznay turbulence model is investigated using this approach. Predicted drag coefficients for the cylinder test-case show significant (15%) improvement over standard steady RANS and are comparable with URANS results. The mean flow-field also shows a significant improvement over URANS. The error in re-attachment length is improved by 180% compared with the steady RANS k-ω model. The wake velocity profile at a location downstream shows improvement and the URANS profile is inaccurate in comparison. For the cavity case, the HJ–NK approach is generally comparable with the other RANS models for measured velocity profiles. Predicted drag coefficients are compared with large eddy simulation. The new approach shows a 20–30% improvement in predicted drag coefficients compared with standard one and two equation RANS models. The shape of the recirculation region within the cavity is also much improved.
The Thermodynamics of Wake Blade Interaction in Axial Flow Turbines: Combined Experimental and Computational Study
Authors: Rose Martin , Schüpbach Peter , Mansour Michel
Published: March 2013

This paper reports on insights into the detailed thermodynamics of axial turbine nozzle guide vane (NGV) wakes as they interact with the rotor blades. The evidence presented is both computational and experimental. Unsteady Reynolds-averaged Navier–Stokes (RANS) simulations are used to compare the experimental observations with theoretical predictions. Output processing with both Eulerian and Lagrangian approaches is used to track the property variation of the fluid particles. The wake is found to be hot and loses heat to the surrounding fluid. The Lagrangian output processing shows that the entropy of the wake will fall due to heat loss as it passes through the rotor and this is corroborated experimentally. The experimental vehicle is a 1.5-stage shroudless turbine with modest Mach numbers of 0.5 and high response instrumentation. The entropy reduction of the wake is determined to be about four times the average entropy rise of the whole flow across the rotor. The results show that the work done by the wake fluid on the rotor is approximately 24% lower than that of the free-stream. The apparent experimental efficiency of the wake fluid is 114% but the overall efficiency of the turbine at midheight is around 95%. It is concluded that intrafluid heat transfer has a strong impact on the loss distribution even in a nominally adiabatic turbine with moderate row exit Mach numbers of 0.5.
Effect of the Biot Number on Metal Temperature of Thermal-Barrier-Coated Turbine Parts—Real Engine Measurements
Authors: Henze Marc , Bogdanic Laura , Muehlbauer Kurt , Schnieder Martin
Published: March 2013

For numerous hot gas parts (e.g., blades or vanes) of a gas turbine, thermal barrier coating (TBC) is used to reduce the metal temperature to a limit that is acceptable for the component and the required lifetime. However, the ability of the TBC to reduce the metal temperature is not constant, it is a function of Biot and Reynolds number. This behavior might lead to a vane's or blade's metal temperature increase at a lower load relative to a reference load condition of the gas turbine (i.e., at lower operating Reynolds number). A measurement campaign has been performed to evaluate metal temperature measurements on uncoated and coated turbine parts in Alstom's GT26 test power plant in Switzerland. Therefore, the impact of varying Reynolds number on the ability of the TBC to protect the turbine components was evaluated. This paper reports on engine-run validation, including details on the application of temperature sensors on thermal-barrier-coated parts. Different methods for the application of thermocouples that were taken into account during the development of the application process are shown. Measurement results for a range of Reynolds number are given and compared to model predictions. Focus of the evaluation is on the measurements underneath the TBC. The impact of different Reynolds number on the ability of the TBC to protect the parts against the hot gas is shown. TBC coated components show under certain circumstances higher metal temperatures at lower load compared to a reference load condition. The measurement values obtained from real engine tests can be confirmed by 1D-model predictions that explain the dependency of the TBC effect on Biot and Reynolds number.
Heat Transfer Measurements in a Leading Edge Geometry With Racetrack Holes and Film Cooling Extraction
Authors: Andrei Luca , Carcasci Carlo , Da Soghe Riccardo , Facchini Bruno , Maiuolo Francesco , Tarchi Lorenzo , Zecchi Stefano
Published: March 2013

An experimental survey on a state of the art leading edge cooling scheme was performed to evaluate heat transfer coefficients (HTC) on a large scale test facility simulating a high pressure turbine airfoil leading edge cavity. The test section includes a trapezoidal supply channel with three large racetrack impingement holes. On the internal surface of the leading edge, four big fins are placed in order to confine impingement jets. The coolant flow impacts the leading edge internal surface, and it is extracted from the leading edge cavity through 24 showerhead holes and 24 film cooling holes. The aim of the present study is to investigate the combined effects of jet impingement and mass flow extraction on the internal heat transfer of the leading edge. A nonuniform mass flow extraction was also imposed to reproduce the effects of the pressure side and suction side external pressure. Measurements were performed by means of a transient technique using narrow band thermochromic liquid crystals (TLCs). Jet Reynolds number and crossflow conditions into the supply channel were varied in order to cover the typical engine conditions of these cooling systems (Rej=10,000-40,000). Experiments were compared with a numerical analysis on the same test case in order to better understand flow interaction inside the cavity. Results are reported in terms of detailed 2D maps, radial-wise, and span-wise averaged values of Nusselt number.
A Model for Simulation of Turbulent Flow With High Free Stream Turbulence Implemented in OpenFOAM®
Authors: Foroutan Hosein , Yavuzkurt Savas
Published: March 2013

A low-Reynolds number k-ε model for simulation of turbulent flow with high free stream turbulence is developed which can successfully predict turbulent kinetic energy profiles, skin friction coefficient, and Stanton number under high free stream turbulence. Modifications incorporating the effects of free stream velocity and length scale are applied. These include an additional term in turbulent kinetic energy transport equation, as well as reformulation of the coefficient in turbulent viscosity equation. The present model is implemented in OpenFOAM CFD code and applied together with other well-known versions of low-Reynolds number k-ε model in flow and heat transfer calculations in a flat plate turbulent boundary layer. Three different test cases based on the initial values of the free stream turbulence intensity (1%, 6.53%, and 25.7%) are considered and models predictions are compared with available experimental data. Results indicate that almost all low-Reynolds number k-ε models, including the present model, give reasonably good results for low free stream turbulence intensity case (1%). However, deviations between current k-ε models predictions and data become larger as turbulence intensity increases. Turbulent kinetic energy levels obtained from these models for very high turbulence intensity (25.7%) show as much as 100% underprediction while skin friction coefficient and Stanton number are overpredicted by more than 70%. Applying the present modifications, predictions of skin friction coefficient, and Stanton number improve considerably (only 15% and 8% deviations in average for very high free stream turbulence intensity). Turbulent kinetic energy levels are vastly improved within the boundary layer as well. It seems like the new developed model can capture the physics of the high free stream turbulence effects.