bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Real-Time Degradation Model for Hardware in the Loop Simulation of Fuel Cell Gas Turbine Hybrid Systems
Authors: Zaccaria Valentina , Traverso Alberto , Tucker David 
Published: August 2015

The theoretical efficiencies of gas turbine fuel cell hybrid systems make them an ideal technology for the future. Hybrid systems focus on maximizing the utilization of existing energy technologies by combining them. However, one pervasive limitation that prevents the commercialization of such systems is the relatively short lifetime of fuel cells, which is due in part to several degradation mechanisms. In order to improve the lifetime of hybrid systems and to examine long-term stability, a study was conducted to analyze the effects of electrochemical degradation in a solid oxide fuel cell (SOFC) model.
The SOFC model was developed for hardware-in-the-loop simulation with the constraint of real-time operation for coupling with turbomachinery and other system components. To minimize the computational burden, algebraic functions were fit to empirical relationships between degradation and key process variables: current density, fuel utilization, and temperature.
Previous simulations showed that the coupling of gas turbines and SOFCs could reduce the impact of degradation as a result of lower fuel utilization and more flexible current demands. To improve the analytical capability of the model, degradation was incorporated on a distributed basis to identify localized effects and more accurately assess potential failure mechanisms. For syngas fueled systems, the results showed that current density shifted to underutilized sections of the fuel cell as degradation progressed. Over-all, the time to failure was increased, but the temperature difference along cell was increased to unacceptable levels, which could not be determined from the previous approach.
Open Loop and Closed Loop Performance of Solid Oxide Fuel Cell Turbine Hybrid Systems During Fuel Composition Changes
Authors: Harun Nor Farida , Tucker David , Adams Thomas A. 
Published: August 2015

The dynamic behavior of a solid oxide fuel cell gas turbine hybrid system (SOFC/GT) from both open and closed loop transients in response to sudden changes in fuel composition was experimentally investigated. A pilot-scale (200kW – 700kW) hybrid facility available at the U.S. Department of Energy, National Energy Technology Laboratory was used to perform the experiments using a combination of numerical models and actual equipment.
In the open loop configuration, the turbine speed was driven by the thermal effluent fed into the gas turbine system, where the thermal effluent was determined by the feedforward fuel cell control system. However, in the closed loop configuration, a load-based speed control system was used to maintain the turbine speed constant at 40,500rpm by adjusting the load on the turbine, in addition to the implementation of the fuel cell system control.
The open loop transient response showed that the impacts of fuel composition changes on key process variables, such as fuel cell thermal effluent, turbine speed and cathode feed stream conditions in the SOFC/GT systems were propagated over the course of the test, except for the cathode inlet temperature. The trajectories of the aforementioned variables are discussed in this paper to better understand the resulting mitigation/propagation behaviors. This will help lead to the development of novel control strategies to mitigate the negative impacts experienced during fuel composition transients of SOFC/GT systems.
Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Acoustic Resonance
Authors: Holzinger F. , Wartzek F. , Nestle M. , Schiffer H.-P. , Leichtfuß S. 
Published: August 2015

This paper investigates the acoustically induced rotor blade vibration that occurred in a state-of-the-art 1.5-stage transonic research compressor. The compressor was designed with the unconventional goal to encounter self-excited blade vibration within its regular operating domain.
Despite the design target to have the rotor blades reach negative aerodamping in the near stall region for high speeds and open inlet guide vane, no vibration occurred in that area prior to the onset of rotating stall. Self-excited vibrations were finally initiated when the compressor was operated at part speed with fully open inlet guide vane along nominal and low operating line. The mechanism of the fluid-structure-interaction behind the self-excited vibration is identified by means of unsteady compressor instrumentation data. Experimental findings point towards an acoustic resonance originating from separated flow in the variable inlet guide vanes. A detailed investigation based on highly resolved wall pressure data confirms this conclusion.
The paper documents the spread in aerodynamic damping calculated by various partners with their respective aeroelastic tools for a single geometry and speed line. This significant spread proves the need for calibration of aeroelastic tools to reliably predict blade vibration. The paper contains a concise categorization of flow induced blade vibration and defines criteria to quickly distinguish the different types of blade vibration. It further gives a detailed description of a novel test compressor and thoroughly investigates the encountered rotor blade vibration.
Multi-Disciplinary Multi-Point Optimization of a Turbocharger Compressor Wheel
Authors: Demeulenaere Alain , Bonaccorsi Jean-Charles , Gutzwiller David , Hu Leon , Sun Harold 
Published: August 2015

The paper describes the application of an optimization method to the redesign of a turbocharger compressor wheel. The starting design presents quite high performance. Previous attempts to improve this design have shown it difficult to increase aerodynamic performance without compromising mechanical stress levels.
The optimization methodology relies on the combination of a genetic algorithm, a neural network, a database, and user generated objective functions. The originality of the paper is that the optimization is not only coupled to a CFD solver, but also to a CSM solver, so that mechanical stresses can be included in the optimization objectives. A parametric model of the solid sector of the blade, back plate and bore zone is built and included in the optimization. The challenging turbocharger test case has allowed gaining experience with design objectives of different nature. The results show that the optimization has been able to improve the aero performance, while also decreasing the peak mechanical stress levels significantly.
Cooling Optimisation Theory: Part 1 — Optimum Wall Temperature, Coolant Exit Temperature and the Effect of Wall/Film Properties on Performance
Authors: Kirollos Benjamin , Povey Thomas 
Published: August 2015

Gas turbine cooling system design is constrained by a maximum allowable wall temperature (dictated by the material and the life requirements of the component), minimum coolant mass flow rate (the requirement to minimise cycle-efficiency cost) and uniform wall temperature (to reduce thermal stresses). These three design requirements form the basis of an iterative design process. The relationship between the requirements has received little discussion in the literature, despite being of interest from both a theoretical and a practical viewpoint. In this paper, we consider the optimum cooling system for parts with both internal and film cooling. We show analytically that the coolant mass flow rate is minimised when the wall temperature is uniform and equal to the maximum allowable wall temperature. Thus, we show that achieving uniform wall temperature achieves minimum coolant flow rate, and vice versa. The purpose is to clarify the interplay between two design requirements that are often discussed separately in the literature. The penalty (in terms of coolant mass flow) associated with cooling non-isothermal components is quantified. We show that a typical high pressure nozzle guide vane (HPNGV) operating isothermally at the maximum allowable wall temperature requires two-thirds the coolant of a typical non-isothermal vane.
The optimum coolant exit temperature is also considered. It is shown analytically that the optimum coolant exit temperature depends on the balance between the mean adiabatic film cooling effectiveness, the non-dimensional mass flow rate and the Biot number of the thermal barrier coating (TBC). For the large majority of gas turbine cooling systems (e.g., a typical HPNGV) it is shown that the optimum coolant exit temperature is equal to the local wall temperature at the point of injection. For a small minority of systems (e.g., long effusion cooling systems operating at low mass flow rates) it is shown that the coolant exit temperature should be minimised.
An approximation relating the wall/film properties, the non-dimensional mass flow, and the overall cooling effectiveness is derived. It is used to estimate the effect of Biot number (TBC and metal), HTC ratio and film properties on the performance of a typical HPNGV and effusion cooling system.
In the companion paper, we show that designs which achieve uniform wall temperature have a particular corresponding internal heat transfer coefficient (HTC) distribution.
Drive Train Over-Speed Prediction for Gas Fuel Based Gas Turbine Power Generation Units
Authors: Forhad M. Moinul I. , Bloomberg Mark 
Published: August 2015

Under all circumstances, an engine and its driven equipment(s) must be prevented from operating at a speed above the maximum allowed speed — to ensure the safety of the equipment, plant and its personnel. However, meeting this requirement is particularly challenging for power generation units where the drive train is composed of electric generators driven by free power turbines (i.e. aerodynamically-coupled power turbines), since during load-shed events or circuit breaker failure, full loss of load happens almost instantly.
During these events, usually the Fuel Metering Valve is fully closed by the Engine Control System and the Fuel Isolation Valve is closed by the safety system. But, fuel gas continues to flow to the system during the closing of the valves, and furthermore, the fuel gas trapped in the piping between the valve and the fuel injectors still has enough pressure to flow to the combustion chamber and add energy to the system, which at that point has almost no external load, thus likely to cause an over-speeding of the drive-train.
This paper is to report a dynamic model created for drive-train over-speed predictions. In this model, fuel flow rate to the engine is calculated based on the principle of conservation of mass together with the fuel gas equation of state. The calculated fuel flow rate is then used to find the amount of power supply to the drive train, which in the next step is converted to the torque applied on the shaft. Finally, Newton’s second law is used to determine the angular acceleration and the angular speed. This approach is applied to two different variations of the Industrial RB211 Engine — the DLE (Dry Low Emission) RB211 and Non-DLE RB211 — which have different designs of the fuel gas system and the burners. For both cases, the results using the modeling approach presented in this paper demonstrate around 99% agreement with the actual measured over-speed values recorded during trip events. The model allows studying the drive train speed for different operating conditions and failure cases, and also makes it easy to understand and quantify the effect of fuel gas system parameter variation on drive-train over-speed.
Reduced dose measurement of absolute myocardial blood flow using dynamic SPECT imaging in a porcine model
Authors: Timmins Rachel , Klein Ran , Petryk Julia , Marvin Brian , Wei Lihui , deKemp Robert A. , Ruddy Terrence D. , Wells R. Glenn 
Published: August 2015

Purpose:Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements provide important additional information over traditional relative perfusion imaging. Recent advances in camera technology have made this possible with single‐photon emission tomography (SPECT). Low dose protocols are desirable to reduce the patient radiation risk; however, increased noise may reduce the accuracy of MBF measurements. The authors studied the effect of reducing dose on the accuracy of dynamic SPECT MBF measurements.Methods:Nineteen 30–40 kg pigs were injected with 370 + 1110 MBq of Tc‐99m sestamibi or tetrofosmin or 37 + 111 MBq of Tl‐201 at rest + stress. Microspheres were injected simultaneously to measure MBF. The pigs were imaged in list‐mode for 11 min starting at the time of injection using a Discovery NM 530c camera (GE Healthcare). Each list file was modified so that 3/4, 1/2, 1/4, 1/8, 1/16, and 1/32 of the original counts were included in the projections. Modified projections were reconstructed with CT‐based attenuation correction and an energy window‐based scatter correction and analyzed with FlowQuant kinetic modeling software using a 1‐compartment model. A modified Renkin‐Crone extraction function was used to convert the tracer uptake rate K1 to MBF values. The SPECT results were compared to those from microspheres.Results:Correlation between SPECT and microsphere MBF values for the full injected activity was r ≥ 0.75 for all 3 tracers and did not significantly degrade over all count levels. The mean MBF and MFR and the standard errors in the estimates were not significantly worse than the full‐count data at 1/4‐counts (Tc99m‐tracers) and 1/2‐counts (Tl‐201).Conclusions:Dynamic SPECT measurement of MBF and MFR in pigs can be performed with 1/4 (Tc99m‐tracers) or 1/2 (Tl‐201) of the standard injected activity without significantly reducing accuracy and precision.
Low tube voltage dual source computed tomography to reduce contrast media doses in adult abdomen examinations: A phantom study
Authors: Thor Daniel , Brismar Torkel B. , Fischer Michael A. 
Published: August 2015

Purpose:To evaluate the potential of low tube voltage dual source (DS) single energy (SE) and dual energy (DE) computed tomography (CT) to reduce contrast media (CM) dose in adult abdominal examinations of various sizes while maintaining soft tissue and iodine contrast‐to‐noise ratio (CNR).Methods:Four abdominal phantoms simulating a body mass index of 16 to 35 kg/m2 with four inserted syringes of 0, 2, 4, and 8 mgI/ml CM were scanned using a 64‐slice DS‐CT scanner. Six imaging protocols were used; one single source (SS) reference protocol (120 kV, 180 reference mAs), four low kV SE protocols (70 and 80 kV using both SS and DS), and one DE protocol at 80/140 kV. Potential CM reduction with unchanged CNRs relative to the 120 kV protocol was calculated along with the corresponding increase in radiation dose.Results:The potential contrast media reductions were determined to be approximately 53% for DS 70 kV, 51% for SS 70 kV, 44% for DS 80 kV, 40% for SS 80 kV, and 20% for DE (all differences were significant, P < 0.05). Constant CNR could be achieved by using DS 70 kV for small to medium phantom sizes (16–26 kg/m2) and for all sizes (16–35 kg/m2) when using DS 80 kV and DE. Corresponding radiation doses increased by 60%–107%, 23%–83%, and 6%–12%, respectively.Conclusions:DS single energy CT can be used to reduce CM dose by 44%–53% with maintained CNR in adult abdominal examinations at the cost of an increased radiation dose. DS dual‐energy CT allows reduction of CM dose by 20% at similar radiation dose as compared to a standard 120 kV single source.
Viral Agents Causing Brown Cap Mushroom Disease of Agaricus bisporus
Authors: Eastwood Daniel , Green Julian , Grogan Helen , Burton Kerry 
Published: August 2015

ABSTRACT

The symptoms of viral infections of fungi range from cryptic to severe, but there is little knowledge of the factors involved in this transition of fungal/viral interactions. Brown cap mushroom disease of the cultivated
Agaricus bisporus
is economically important and represents a model system to describe this transition. Differentially expressed transcript fragments between mushrooms showing the symptoms of brown cap mushroom disease and control white noninfected mushrooms have been identified and sequenced. Ten of these RNA fragments have been found to be upregulated over 1,000-fold between diseased and nondiseased tissue but are absent from the
Agaricus bisporus
genome sequence and hybridize to double-stranded RNAs extracted from diseased tissue. We hypothesize that these transcript fragments are viral and represent components of the disease-causing agent, a bipartite virus with similarities to the family
Partitiviridae
. The virus fragments were found at two distinct levels within infected mushrooms, at raised levels in infected, nonsymptomatic, white mushrooms and at much greater levels (3,500 to 87,000 times greater) in infected mushrooms exhibiting brown coloration. In addition, differential screening revealed 9 upregulated and 32 downregulated host
Agaricus bisporus
transcripts. Chromametric analysis was able to distinguish color differences between noninfected white mushrooms and white infected mushrooms at an early stage of mushroom growth. This method may be the basis for an “on-farm” disease detection assay.
Distribution and Genetic Diversity of Bacteriocin Gene Clusters in Rumen Microbial Genomes
Authors: Azevedo Analice C. , Bento Cláudia B. P. , Ruiz Jeronimo C. , Queiroz Marisa V. , Mantovani Hilário C. 
Published: August 2015

ABSTRACT

Some species of ruminal bacteria are known to produce antimicrobial peptides, but the screening procedures have mostly been based on
in vitro
assays using standardized methods. Recent sequencing efforts have made available the genome sequences of hundreds of ruminal microorganisms. In this work, we performed genome mining of the complete and partial genome sequences of 224 ruminal bacteria and 5 ruminal archaea to determine the distribution and diversity of bacteriocin gene clusters. A total of 46 bacteriocin gene clusters were identified in 33 strains of ruminal bacteria. Twenty gene clusters were related to lanthipeptide biosynthesis, while 11 gene clusters were associated with sactipeptide production, 7 gene clusters were associated with class II bacteriocin production, and 8 gene clusters were associated with class III bacteriocin production. The frequency of strains whose genomes encode putative antimicrobial peptide precursors was 14.4%. Clusters related to the production of sactipeptides were identified for the first time among ruminal bacteria. BLAST analysis indicated that the majority of the gene clusters (88%) encoding putative lanthipeptides contained all the essential genes required for lanthipeptide biosynthesis. Most strains of
Streptococcus
(66.6%) harbored complete lanthipeptide gene clusters, in addition to an open reading frame encoding a putative class II bacteriocin. Albusin B-like proteins were found in 100% of the
Ruminococcus albus
strains screened in this study. The
in silico
analysis provided evidence of novel biosynthetic gene clusters in bacterial species not previously related to bacteriocin production, suggesting that the rumen microbiota represents an underexplored source of antimicrobial peptides.
Interactions between Cooccurring Lactic Acid Bacteria in Honey Bee Hives
Authors: Rokop Z. P. , Horton M. A. , Newton I. L. G. 
Published: August 2015

ABSTRACTIn contrast to the honey bee gut, which is colonized by a few characteristic bacterial clades, the hive of the honey bee is home to a diverse array of microbes, including many lactic acid bacteria (LAB). In this study, we used culture, combined with sequencing, to sample the LAB communities found across hive environments. Specifically, we sought to use network analysis to identify microbial hubs sharing nearly identical operational taxonomic units, evidence which may indicate cooccurrence of bacteria between environments. In the process, we identified interactions between noncore bacterial members (FructobacillusandLactobacillaceae) and honey bee-specific “core” members. BothFructobacillusandLactobacillaceaecolonize brood cells, bee bread, and nectar and may serve the role of pioneering species, establishing an environment conducive to the inoculation by honey bee core bacteria. Coculture assays showed that these noncore bacterial members promote the growth of honey bee-specific bacterial species. Specifically,Fructobacillusby-products in spent medium supported the growth of the Firm-5 honey bee-specific cladein vitro. Metabolic characterization ofFructobacillususing carbohydrate utilization assays revealed that this strain is capable of utilizing the simple sugars fructose and glucose, as well as the complex plant carbohydrate lignin. We testedFructobacillusfor antibiotic sensitivity and found that this bacterium, which may be important for establishment of the microbiome, is sensitive to the commonly used antibiotic tetracycline. Our results point to the possible significance of “noncore” and environmental microbial community members in the modulation of honey bee microbiome dynamics and suggest that tetracycline use by beekeepers should be limited.
Changes in Microbial Biofilm Communities during Colonization of Sewer Systems
Authors: Auguet O. , Pijuan M. , Batista J. , Borrego C. M. , Gutierrez O. 
Published: August 2015

ABSTRACT

The coexistence of sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) in anaerobic biofilms developed in sewer inner pipe surfaces favors the accumulation of sulfide (H
2
S) and methane (CH
4
) as metabolic end products, causing severe impacts on sewerage systems. In this study, we investigated the time course of H
2
S and CH
4
production and emission rates during different stages of biofilm development in relation to changes in the composition of microbial biofilm communities. The study was carried out in a laboratory sewer pilot plant that mimics a full-scale anaerobic rising sewer using a combination of process data and molecular techniques (e.g., quantitative PCR [qPCR], denaturing gradient gel electrophoresis [DGGE], and 16S rRNA gene pyrotag sequencing). After 2 weeks of biofilm growth, H
2
S emission was notably high (290.7 ± 72.3 mg S-H
2
S liter
−1
day
−1
), whereas emissions of CH
4
remained low (17.9 ± 15.9 mg COD-CH
4
liter
−1
day
−1
). This contrasting trend coincided with a stable SRB community and an archaeal community composed solely of methanogens derived from the human gut (i.e.,
Methanobrevibacter
and
Methanosphaera
). In turn, CH
4
emissions increased after 1 year of biofilm growth (327.6 ± 16.6 mg COD-CH
4
liter
−1
day
−1
), coinciding with the replacement of methanogenic colonizers by species more adapted to sewer conditions (i.e.,
Methanosaeta
spp.). Our study provides data that confirm the capacity of our laboratory experimental system to mimic the functioning of full-scale sewers both microbiologically and operationally in terms of sulfide and methane production, gaining insight into the complex dynamics of key microbial groups during biofilm development.