bluuebunny/crossref_metadata_2025_split huggingface dataset:
The interplay between daily affect and sleep: a 2‐week study of young women
Authors: Kalmbach David A. , Pillai Vivek , Roth Thomas , Drake Christopher L. 
Published: August 2014

SummaryLittle attention has been paid to the relation between daily affect and sleep, as most prior studies have focused instead on the role of pathological mood in the context of sleep disturbance. However, understanding the transaction between normal variations in emotional experiences and sleep can shed light on the premorbid vulnerabilities that trigger the evolution of affect and sleep into more problematic states. The present study used a 2‐week daily sampling approach to examine the impact of day‐to‐day variations in positive and negative affect on nightly self‐reported sleep‐onset latency, sleep duration and sleep quality in a sample of young women. Hierarchical linear modelling revealed temporal relations between positive and negative affect states and sleep parameters. Specifically, different aspects of both positive and negative affect were uniquely predictive of sleep indices, with sadness and serenity acting as the most consistent predictors. Additionally, better sleep quality was predictive of greater happiness the following day. These results highlight the importance of how our daily emotional experiences influence our nightly sleep and, in turn, how our sleep has an impact on our daily affect. Moreover, our findings may offer insight into the progression of normative levels of affect and sleep as they develop into comorbid depression, anxiety and insomnia.
Effects of sleep/wake history and circadian phase on proposed pilot fatigue safety performance indicators
Authors: Gander Philippa H. , Mulrine Hannah M. , van den Berg Margo J. , Smith A. Alexander T. , Signal T. Leigh , Wu Lora J. , Belenky Gregory 
Published: August 2014

SummaryThe Karolinska Sleepiness Scale and Samn–Perelli fatigue ratings, and psychomotor vigilance task performance are proposed as measures for monitoring commercial pilot fatigue. In laboratory studies, they are sensitive to sleep/wake history and circadian phase. The present analyses examined whether they reliably reflect sleep/wake history and circadian phase during transmeridian flight operations. Data were combined from four studies (237 pilots, 730 out‐and‐back flights between 13 city pairs, 1–3‐day layovers). Sleep was monitored (wrist actigraphy, logbooks) before, during and after trips. On duty days, sleepiness, fatigue and mean response speed were measured pre‐flight and at the top of the descent. Mixed‐model analysis of variance examined associations between these measures and sleep/wake history, after controlling for operational factors. Circadian phase was approximated by local (domicile) time in the city where each trip began and ended. More sleep in the 24 h prior to duty was associated with lower pre‐flight sleepiness and fatigue and faster response speed. Sleepiness and fatigue were greater before flights departing during the domicile night and early morning. At the top of the descent, pilots felt less sleepy and fatigued after more in‐flight sleep and less time awake. Flights arriving in the early–mid‐morning (domicile time) had greater sleepiness and fatigue and slower response speeds than flights arriving later. Subjective ratings showed expected associations with sleep/wake history and circadian phase. The response speed showed expected circadian variation but was not associated with sleep/wake history at the top of the descent. This may reflect moderate levels of fatigue at this time and/or atypically fast responses among pilots.
Assessment of the Effect of Population and Diary Sampling Methods on Estimation of School‐Age Children Exposure to Fine Particles
Authors: Che W. W. , Frey H. Christopher , Lau Alexis K. H. 
Published: August 2014

Population and diary sampling methods are employed in exposure models to sample simulated individuals and their daily activity on each simulation day. Different sampling methods may lead to variations in estimated human exposure. In this study, two population sampling methods (stratified‐random and random‐random) and three diary sampling methods (random resampling, diversity and autocorrelation, and Markov‐chain cluster [MCC]) are evaluated. Their impacts on estimated children's exposure to ambient fine particulate matter (PM2.5) are quantified via case studies for children in Wake County, NC for July 2002. The estimated mean daily average exposure is 12.9 μg/m3 for simulated children using the stratified population sampling method, and 12.2 μg/m3 using the random sampling method. These minor differences are caused by the random sampling among ages within census tracts. Among the three diary sampling methods, there are differences in the estimated number of individuals with multiple days of exposures exceeding a benchmark of concern of 25 μg/m3 due to differences in how multiday longitudinal diaries are estimated. The MCC method is relatively more conservative. In case studies evaluated here, the MCC method led to 10% higher estimation of the number of individuals with repeated exposures exceeding the benchmark. The comparisons help to identify and contrast the capabilities of each method and to offer insight regarding implications of method choice. Exposure simulation results are robust to the two population sampling methods evaluated, and are sensitive to the choice of method for simulating longitudinal diaries, particularly when analyzing results for specific microenvironments or for exposures exceeding a benchmark of concern.
Biomass-Based, Small-Scale, Distributed Generation of Electricity and Heat Using Integrated Gas Turbine-Fuel Cell Systems
Authors: Buhre B. J. P. , Andries J. 
Published: August 2014

The use of a biomass gasifier that drives a gas turbine integrated with a fuel cell, is a potentially very attractive way to generate electricity and heat with a high efficiency and very low emissions. The application of catalytic combustion systems can decrease the emissions even further.
A number of technical and non-technical developments during the last 5 years have significantly enhanced the opportunities for small-scale, distributed power generation, especially for systems based on biomass fuels. These developments are: the liberalisation of the energy market, the growing needs for electricity and heat in developing countries, the increasing demand for ‘green’ or ‘sustainable’ electricity, the near-commercial availability of maintenance-low microturbine generator packages and developments in the field of high temperature fuel cells.
Preliminary system studies have shown that the integration of the different subsystems needs careful evaluation in order to realise the expected high efficiencies. To enable the assessment of the technical feasibility of potentially attractive system designs, adequate, experimentally validated knowledge with regard to biomass gasification, pressurised combustion of the fuel gas and the gas cleaning steps is required.
Possible system designs based on a combination of electrochemical and thermochemical fuel conversion steps are examined and analysed with regard to efficiency, emission and costs.
A system design for application on commercial scale based on present day technology will be considered. At Delft University of Technology, a biomass gasifier has been set up and a conceptual design for a pilot system, to be tested in the slipstream of the Delft 1.5 MWth process development unit, will be presented. The process development unit is described in more detail in [Hoppesteyn, et. al., 1998] and [de Jong et. al., 1998]. In this study, it has been attempted to integrate an SOFC with an existing micro gas turbine that has not especially been adjusted for the integration with the SOFC.
The Use of Hot-Wire Anemometry to Investigate Unsteady Wake-Induced Boundary-Layer Development on a High Lift LP Turbine Cascade
Authors: Wolff Stefan , Brunner Stefan , Fottner Leonhard 
Published: August 2014

Recent research has revealed positive effects of unsteady flow on the development of boundary layers in turbine cascades, especially at conditions with a laminar suction side separation bubble at low Reynolds-numbers. Compared to steady flow a reduction of total pressure loss coefficient over a broad range of Reynolds-numbers has been shown. Taking into account the positive effects of wake-induced transition already during the design process, new high lift bladings with nearly the same low losses at unsteady inlet flow conditions could be achieved. This leads to a reduction of weight and cost of the whole turbine module for a constant stage loading.
Unsteady flow in turbomachines is caused by the relative motion of rotor and stator rows. For simulating a moving blade row upstream of a linear cascade in the High Speed Cascade Wind Tunnel of the Universität der Bundeswehr München, a wake generator has been designed and built. The wakes are generated with bars, moving with a velocity of up to 40 m/s in the test section upstream of the cascade inlet plane.
Unsteady flow causes the transition on the surface of the suction side of a low pressure turbine blade to move upstream whenever an incoming wake is present on the surface, moreover a laminar separation bubble can be diminished or even suppressed. In order to detect the effects of wakes on the boundary layer development a new hot-wire data acquisition system is required.
Due to the fact that hot-wires give a good insight into boundary layer development a new hot-wire data acquisition system has been set up. The anemometry system is able of acquiring four channels simultaneously, therefore being capable of logging a triple hot-wire sensor and a bar trigger simultaneously. One further channel is utilised for a once-per revolution trigger. The once-per revolution trigger is used to start the measurement of one data block. Using the well established ensemble averaging technique, 300 ensembles each consisting of 5 wake passing periods have been acquired. Ensemble averaging can be directly performed without any data reduction.
The adaptation of this new hot-wire anemometry data acquisition system to the High Speed Cascade Wind Tunnel of the Universität der Bundeswehr München is pointed out. First results on unsteady periodic boundary layer development of a highly loaded low pressure turbine cascade under unsteady inlet flow conditions are presented. During the present investigation four boundary layer traverses, ranging from x/lax = 0.82 to x/lax = 0.99 (suction side), at steady and unsteady inlet flow conditions (Ubar = 10 m/s) at an outlet Reynolds-number of Re2th = 100000 have been conducted.
Synchronized LDV Measurement in Centrifugal Impeller: Seeding Insemination Set Up and CFD Comparison
Authors: De Lucia M. , Mengoni C. P. , Boncinelli P. , Corradini U. 
Published: August 2014

Investigation of flow is necessary for turbomachinery performance analysis.
The development of high performance centrifugal impellers leads to use of higher and higher rotational speeds and smaller and smaller impellers.
The use of intrusive probe for flow evaluation is often inadequate since the probe size can be comparable with the flow passage area and can cause flow distortion so large as to invalidate measurements.
Therefore the use of non-intrusive measurement techniques, which will not alter the flow, is required.
Laser Doppler Velocimetry (LDV) provides an accurate velocity valuation through non-intrusive measurements even in the small hub to shroud area passage.
The right set up of the LDV system is fundamental for accurate measurement; investigated area and working conditions are often completely unknown, so erroneous data, due to system set up, are not easily recognizable. The definition of lens, seeding, insemination technique and LDV parameters can be a source of errors not detectable in measurement phases. Special equipment (seeding inseminating test system and a dedicated wind tunnel) is developed to overcome these problems and to define the right parameters and working conditions to be used in turbomachinery applications. Details of LDV set up are reported in this paper.
In real turbomachinery applications standard LDV measurement (time averaged velocity) could be effected by a non-homogeneous distribution of seeding: e.g. in an impeller in the presence of jet and wake, so it is necessary to link seeding particle passages to their position through the time history in a non-ambiguous way. A customized synchronization technique is presented. Validation of measurements has been achieved by comparing LDV data with results of 3D fully viscous computations.
Chemical Vapour Deposition of TBC: An Alternative Process for Gas Turbine Components
Authors: Wahl G. , Nemetz W. , Giannozzi M. , Rushworth S. , Baxter D. , Archer N. , Cernuschi F. , Boyle N. 
Published: August 2014

This paper deals with a development of a new process for the deposition of Thermal Barrier Coatings (TBC) based on Chemical Vapour Deposition (CVD). The research program started in September 1998 under a BRITE/Euram III project.
The CVD process involves the evaporation of zirconium and yttrium starting from metal-organic precursors and their reaction with oxygen in a hot wall reactor in order to deposit TBC layers.
The influence of different deposition parameters such as evaporation temperature, pressure and substrate temperature on structure, deposition rate and process yield are described. The characterisation of different precursors behaviour is also described. Preliminary results, obtained with optimised conditions, have shown ZrO2-Y2O3 columnar layers with deposition rates of interest from an industrial point of view.
Reduced NOx Diffusion Flame Combustors for Industrial Gas Turbines
Authors: Feitelberg Alan S. , Tangirala Venkat E. , Elliott Richard A. , Pavri Roointon E. , Schiefer Richard B. 
Published: August 2014

This paper describes reduced NOx, diffusion flame combustors that have been developed for both simple cycle and regenerative cycle MS3002 and MS5002 gas turbines. Laboratory tests have shown that when firing with natural gas, without water or steam injection, NOx emissions from the new combustors are about 40% lower than NOx emissions from the standard combustors. CO emissions are virtually unchanged at base load, but increase at part load conditions. Commercial demonstration tests have confirmed the laboratory results.
The standard combustors on both the MS3002 and MS5002 gas turbine are cylindrical cans, approximately 10.5 inches (27 cm) in diameter. A single fuel nozzle is centered at the inlet to each can and produces a swirl stabilized diffusion flame. The walls of the cans are louvered for cooling, and contain an array of mixing and dilution holes that provide the air needed to complete combustion and dilute the burned gas to the desired turbine inlet temperature. The MS3002 turbine is equipped with six combustor cans, while the MS5002 turbine is equipped with twelve combustors.
The new, reduced NOx emissions combustors (referred to as a “lean head end”, or LHE, combustors) retain all of the key features of the conventional combustors; the only major difference is the arrangement of the mixing and dilution holes in the cylindrical combustor cans. By optimizing the number, diameter, and location of these holes, NOx emissions can be reduced considerably. Minor changes are also sometimes made to the combustor cap. The materials of construction, pressure drop, and fuel nozzle are all unchanged.
The differences in NOx emissions between the standard and LHE combustors, as well as the variations in NOx emissions with firing temperature, are well correlated using turbulent flame length arguments. Details of this correlation are presented.
Prediction and Measurement of Thermoacoustic Improvements in Gas Turbines With Annular Combustion Systems
Authors: Krüger Uwe , Hüren Jens , Hoffmann Stefan , Krebs Werner , Flohr Patrick , Bohn Dieter 
Published: August 2014

Environmental compatibility requires low emission burners for gas turbine power plants. In the past, significant progress has been made developing low NOx and CO burners by introducing lean premixed techniques in combination with annular combustion chambers. Unfortunately, these burners often have a more pronounced tendency to produce combustion-driven oscillations than conventional burner designs. The oscillations may be excited to such an extent that the risk of engine failure occurs.
For this reason, the prediction of these thermoacoustic instabilities in the design phase of an engine becomes more and more important. A method based on linear acoustic four-pole elements has been developed to predict instabilities of the ring combustor of the 3A-series gas turbines (Krüger et al. (1999b)). The complex network includes the whole combustion system starting from both compressor outlet and fuel supply system and ending at the turbine inlet. The flame frequency response was determined by a transient numerical simulation (step-function approach).
Based on this method, possible improvements for the gas turbine are evaluated in this paper.
First, the burner impedance is predicted theoretically and compared with results from measurements on a test rig for validation of the prediction approach. Next, the burner impedance in a gas turbine combustion system is analyzed and improved thermoacoustically. Stability analyses for the gas turbine combustion system show the positive impact of this improvement.
Second, the interaction of the acoustic parts of the gas turbine system has been detuned systematically in circumferential direction of the annular combustion chamber in order to find a more stable configuration. Stability analyses show the positive effect of this measure as well. The results predicted are compared with measurements from engine operation.
The comparisons of prediction and measurements show the applicability of the prediction method in order to evaluate the thermoacoustic stability of the combustor as well as to define possible countermeasures.
Flamelet Model of NOx in a Diffusion Flame Combustor
Authors: Volkov Dmitry V. , Belokon Alexandr A. , Lyubimov Dmitry A. , Zakharov Vladimir M. , Opdyke George 
Published: August 2014

This paper describes a model used for the prediction of the formation of nitrogen oxides in modifications of an industrial diffusion flame, natural gas fueled can combustor. The flow field inside the modified combustors is calculated using a Navier-Stokes solver. A fast chemistry assumption is used for modeling the heat release. Calculated turbulence parameters are then used for the calculation of the NOx formation rate in the post-processing mode with the aid of a flamelet model. The flamelet model permits the use of detailed kinetics with only minimal computational expense. The dependence of the NOx formation rate on the mixture fraction and scalar dissipation is calculated separately for each given condition.
The validation of the model predictions is based on field test data taken earlier on several low NOx modifications recently applied to an industrial, reverse flow can type combustor. The reduced level of NOx emissions was achieved in these modifications by changes in the air distribution within the combustor liner. A comparison of the predicted and measured NOx emission levels shows good potential of the flamelet model.
Evaluation of Advanced Two-Phase Flow and Combustion Models for Predicting Low Emission Combustors
Authors: Klose G. , Schmehl R. , Meier R. , Meier G. , Koch R. , Wittig S. , Hettel M. , Leuckel W. , Zarzalis N. 
Published: August 2014

The development of low emission aero engine combustors strongly depends on the availability of accurate and efficient numerical models. The prediction of the interaction between two-phase flow and chemical combustion is one of the major objectives of the simulation of combustor flows.
In this paper, predictions of a swirl stabilized model combustor are compared to experimental data. The computational method is based on an Eulerian two-phase model in conjunction with an Eddy Dissipation (ED) and a presumed-shape-PDF (JPDF) combustion model.
The combination of an Eulerian two-phase model with a JPDF combustion model is a novelty. It was found to give good agreement to the experimental data.
Use of Chromium Containing Fuel Additive to Reduce High Temperature Corrosion of Hot Section Parts
Authors: Stalder Jean-Pierre , Huber Peter A. 
Published: August 2014

The use of “clean” fuel is a prerequisite at today’s elevated gas turbine firing temperature, modern engines are more sensitive to high temperature corrosion if there are impurities present in the fuel and/or in the combustion air. It is a common belief that distillate grade fuels are contaminant-free, which is often not true. Frequently operators burning distillates ignore the fuel quality as a possible source of difficulties. This matter being also of concern in plants mainly operated on natural gas and where distillate fuel oil is the back-up fuel. Distillates may contain water, dirt and often trace metals such as sodium, vanadium and lead which can cause severe damages to the gas turbines. Sodium being very often introduced through contamination with seawater during the fuel storage and delivery chain to the plant, and in combination, or with air borne salt ingested by the combustion air. Excursions of sodium in treated crude or heavy fuel oil can occur during unnoticed malfunctions of the fuel treatment plant, when changing the heavy fuel provenience without centrifuge adjustment, or by inadequate fuel handling. For burning heavy fuel, treatment with oil-soluble magnesium fuel additive is state of the art to inhibit hot corrosion caused by vanadium. Air borne salts, sodium, potassium and lead contaminated distillates, gaseous fuels, washed and unwashed crude and residual oil can not be handled by simple magnesium based additives. The addition of elements like silicon and/or chromium is highly effective in reducing turbine blade hot corrosion and hot section fouling.
This paper describes field experience with the use of chromium containing fuel additive to reduce high temperature corrosion of hot section parts, as well as the interaction of oil-soluble chromium and magnesium-chromium additives on material behaviour of blades and vanes, and their economical and environmental aspects.
Numerical Simulation of Swirl-Stabilized Premixed Flames With a Turbulent Combustion Model Based on a Systematically Reduced 6-Step Reaction Mechanism
Authors: Bohn Dieter E. , Lepers Joachim 
Published: August 2014

This paper presents the application of a detailed combustion model for turbulent premixed combustion to a swirl-stabilized premix burner. Computations are carried out for atmospheric pressure and elevated pressure of 9 atm. Results of computations for atmospheric pressure are compared to experimental data.
The combustion model is of the joint-pdf type. The model is based on the characteristics of turbulent combustion under conditions typical for gas turbine burners. It incorporates a systematically reduced 6-step reaction mechanism yielding direct computation of radical concentrations via transport equations or steady-state assumptions. The model is able to simulate combustion of fuel gases containing methane, carbon monoxide, hydrogen, carbon dioxide and water. It is therefore applicable to both methane and low-BTU fuel gas combustion.
Based on computed radical concentrations, a post-processor for NOx-formation is applied. This post-processor considers thermal formation of nitrogen oxides and NO-formation via the nitrous-oxide path.