bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ecological impacts of the late Quaternary megaherbivore extinctions
Authors: Gill Jacquelyn L. 
Published: November 2013

SummaryAs a result of the late Quaternary megafaunal extinctions (50 000–10 000 before present (BP)), most continents today are depauperate of megaherbivores. These extinctions were time‐transgressive, size‐ and taxonomically selective, and were caused by climate change, human hunting, or both. The surviving megaherbivores often act as ecological keystones, which was likely true in the past. In spite of this and extensive research on the causes of the Late Quaternary Extinctions, the long‐term ecological consequences of the loss of the Pleistocene megafauna remained unknown until recently, due to difficulties in linking changes in flora and fauna in paleorecords. The quantification of Sporormiella and other dung fungi have recently allowed for explicit tests of the ecological consequences of megafaunal extirpations in the fossil pollen record. In this paper, I review the impacts of the loss of keystone megaherbivores on vegetation in several paleorecords. A growing number of studies support the hypothesis that the loss of the Pleistocene megafauna resulted in cascading effects on plant community composition, vegetation structure and ecosystem function, including increased fire activity, novel communities and shifts in biomes. Holocene biota thus exist outside the broader evolutionary context of the Cenozoic, and the Late Quaternary Extinctions represent a regime shift for surviving plant and animal species.
Neonatal Hyperpigmentation: Diagnosis of Familial Glucocorticoid Deficiency with a Novel Mutation in the Melanocortin‐2 Receptor Gene
Authors: Jacoby Elad , Barzilai Aviv , Laufer Joseph , Pade Shai , Anikster Yair , Pinhas‐Hamiel Orit , Greenberger Shoshana 
Published: November 2013

AbstractFamilial glucocorticoid deficiency (FGD), a rare autosomal recessive disorder of insensitivity to adrenocorticotropic hormone (ACTH), is characterized by isolated glucocorticoid deficiency and preserved mineralocorticoid production. The clinical features include generalized hyperpigmentation, hypoglycemia, failure to thrive, and recurrent infections. Here we describe the case of an infant who exhibited generalized hyperpigmentation and hypoglycemia. A high morning blood ACTH level and low blood cortisol level confirmed the diagnosis of FGD. The patient was found to be homozygous for a novel mutation in the melanocortin‐2 receptor gene (635insC, I154H). Early initiation of corticosteroid treatment led to normalization of morning blood ACTH levels and the patient thrived, with subsequent fading of the hyperpigmentation.
Preadjusted Non-Parametric Estimation of a Conditional Distribution Function
Authors: Veraverbeke Noël , Gijbels Irène , Omelka Marek 
Published: November 2013

SummaryThe paper deals with non-parametric estimation of a conditional distribution function. We suggest a method of preadjusting the original observations non-parametrically through location and scale, to reduce the bias of the estimator. We derive the asymptotic properties of the estimator proposed. A simulation study investigating the finite sample performances of the estimators discussed is provided and reveals the gain that can be achieved. It is also shown how the idea of the preadjusting opens the path to improved estimators in other settings such as conditional quantile and density estimation, and conditional survival function estimation in the case of censored data.
Two-stage Adaptive Randomization for Delayed Response in Clinical Trials
Authors: Xu Jiajing , Yin Guosheng 
Published: November 2013

SummaryDespite the widespread use of equal randomization in clinical trials, response-adaptive randomization has attracted considerable interest. There is typically a prerun of equal randomization before the implementation of response-adaptive randomization, although it is often not clear how many subjects are needed in this prephase, and in practice the number of patients in the equal randomization stage is often arbitrary. Another concern that is associated with realtime response-adaptive randomization is that trial conduct often requires patients' responses to be immediately available after the treatment, whereas clinical responses may take a relatively long period of time to exhibit. To resolve these two issues, we propose a two-stage procedure to achieve a balance between power and response, which is equipped with a likelihood ratio test before skewing the allocation probability towards a better treatment. Furthermore, we develop a non-parametric fractional model and a parametric survival design with an optimal allocation scheme to tackle the common problem caused by delayed response. We evaluate the operating characteristics of the two-stage designs through extensive simulation studies and illustrate them with a human immunodeficiency virus clinical trial. Numerical results show that the methods proposed satisfactorily resolve the arbitrary size of the equal randomization phase and the delayed response problem in response-adaptive randomization.
The plant fossil record reflects just two great extinction events
Authors: Cascales‐Miñana Borja , Cleal Christopher J. 
Published: November 2013

AbstractFive great taxonomic extinctions (the so‐called ‘Big Five Mass Extinctions’) are widely recognized in life history, at the end of the Ordovician, Frasnian (Late Devonian), Permian, Triassic and Cretaceous. All of them were originally identified in the marine fossil record and have been interpreted as the result of abrupt global environmental changes. Previous evidence has suggested that terrestrial biota were also subjected to ecological disruption during these events, but it is unknown whether they suffered the same level of large‐scale taxonomic disruption as marine organisms. Here we show that the plant fossil record in fact only provides evidence of two mass taxonomic extinction events, one through the Carboniferous‐Permian transition, the other during middle‐late Permian times. This differs significantly from the mass extinctions recognized in the marine realm and suggests that vascular plants have a special capacity for surviving abrupt environmental changes.
Advances in the Development of a Micro-Gas Turbine Engine at Onera
Authors: Dessornes O. , Landais S. , Valle R. , Fourmaux A. , Burguburu S. , Zwyssig C. , Kozanecki Z. 
Published: November 2013

To reduce the size and weight of power generation machines for portable devices, several systems to replace the currently used heavy batteries are being investigated worldwide. As micro gas turbines are expected to offer the highest power density, several research groups launched programs to develop ultra micro gas turbines: IHI firm (Japan), PowerMEMS Consortium (Belgium).
At Onera, a research program called DecaWatt is under development in order to realize a demonstrator of a micro gas turbine engine in the 50 to 100 Watts electrical power range. A single-stage gas turbine is currently being studied. First of all, a calculation of the overall efficiency of the micro gas turbine engine has been carried out according to the pressure ratio, the turbine inlet temperature and the compressor and turbine efficiencies. With realistic hypotheses, we could obtain an overall efficiency of about 5% to 10% which leads to around 200 W/kg when taking into account the mass of the micro gas turbine engine, its electronics, fuel and packaging. Moreover, the specific energy could be in the range 300 to 600 Wh/kg which exceeds largely the performance of secondary batteries.
To develop such a micro gas turbine engine, experimental and computational work focused on:
• a 10 mm in diameter centrifugal compressor, with the objective to obtain a pressure ratio of about 2.5
• a radial inflow turbine
• journal and thrust gas bearings (lobe bearings and spiral grooves) and their manufacturing
• a small combustor working with hydrogen or hydrocarbon gaseous fuel (propane)
• a high rotation speed micro-generator
• the choice of materials
Components of this tiny engine were tested prior to the test with all the parts assembled together. Tests of the generator at 700,000 rpm showed a very good efficiency of this component. In the same way, compressor testing has been performed up to 500,000 rpm and has shown that the nominal compression rate at the 840,000 rpm nominal speed should be nearly reached.
Design and Development of the Inter-Turbine Structure and Power Turbine for MTR390-E Turboshaft Engine
Authors: de la Calzada Pedro , Villanueva Miguel A. , Parra Jorge , Ruiz-Gopegui Juan I. 
Published: November 2013

The MTR390-E is a turboshaft engine of 1000 kW class developed for the TIGER European helicopter. The project was launched back in 2004 and was certified in 2011. The engine is based on the previous MTR390-2C engine but redesigned for 14% more power at high and hot conditions. ITP is the design authority of the inter-turbine duct (ITD) and structure (IC) and the two stages Power Turbine (PT) as part of the MTRI European consortium (MTU, Turbomeca, RR, ITP) for the design and development of the Enhanced engine.
The requirement of higher power, while maintaining the physical envelope of the engine for avoiding changes in the helicopter, led to higher mass flow and turbine inlet temperature. Consequently, the Mach number along the ITD and the PT was increased. A local increase in the flowpath around the area of the ITD and the NGV1 maximum thickness is introduced to avoid high peak Mach numbers and to reduce the flow diffusion. The PT aerofoils feature higher flow velocities leading to transonic Mach numbers at the suction side. The increase in temperature drove the introduction of internal cooling on the ITD and the NGV1 to maintain similar materials while avoiding risk of melting at Super Emergency Conditions (SUP).
Due to the high shaft rotation speed and high operating temperatures the blades are subject to very high mechanical demanding conditions. Single crystal materials are used in both stages where also tip shroud cut outs were introduced to reduce centrifugal stresses. Life requirements were met in both statics and rotating parts.
A complete development test plan was performed to achieve certification and qualification with 7 development engines and 4 flight proto engines. Performance was demonstrated at sea level and altitude conditions.
Successful mechanical condition of parts was obtained after the 150-hrs Type Test plus additional SUP shots. Also good conditions were obtained after sand ingestion test. Good mechanical robustness was proved all along the development programme.
A Novel Methodology for Optimal Design of Compressor Plants Using Probabilistic Plant Design
Authors: Kurz Rainer , Thorp Joseph M. , Zentmyer Eric G. , Brun Klaus 
Published: November 2013

Equipment sizing decisions in the Oil and Gas Industry often have to be made based on incomplete data. Often, the exact process conditions are based on numerous assumptions about well performance, market conditions, environmental conditions and others. Since the ultimate goal is to meet production commitments, the traditional way of addressing this is, to use worst case conditions, and often adding margins onto these. This will invariably lead to plants that are oversized, in some instances by large margins. In reality, the operating conditions are very rarely the assumed worst case conditions, but they are usually more benign most of the time. Plants designed based on worst case conditions, once in operation, will therefore usually not operate under optimum conditions, have reduced flexibility, and therefore cause both higher capital expenses and operating expenses.
The authors outline a new probabilistic methodology that provides a framework for more intelligent process-machine designs. A standardized framework using Monte Carlo simulation and risk analysis is presented that more accurately defines process uncertainty and its impact on machine performance. Case studies are presented that highlight the methodology as applied to critical turbo-machinery.
SOFC/mGT Coupling: Different Options With Standard Boosters
Authors: Larosa Luca , Ferrari Mario L. , Magistri Loredana , Massardo Aristide F. 
Published: November 2013

In this paper an innovative SOFC hybrid system is proposed, equipped with ejector-based cathodic recirculation. The cathodic flow is preheated by recirculating hot exhausts. However, this approach needs higher pressure values than those available with commercial micro gas turbines (mGT): a possible but expensive solution could be to design a completely new mGT. Another option could be to use a booster with the function of re-compressor installed between the mGT compressor and the ejector (in order to increase ejector inlet pressure). This choice allows the use of commercial machines with a substantial cost reduction by comparison with designing a new micro gas turbine. Moreover, this layout is able to separate the compressor ratio of the mGT from the ejector inlet pressure, generating more flexibility from the point of view of the control system.
In this paper, a thermodynamic study of this machine coupling is carried out considering the hybrid system emulator developed by TPG at the University of Genoa. For this purpose, three different boosting approaches were examined with a steady-state model built in Matlab-Simulink environment. The results presented here were obtained to show emulator performance and flexibility. Available power and thermal aspects are discussed in detail.
Flow Field Investigations on the Effect of Rib Placement in a Cooling Channel With Film-Cooling
Authors: Kunze Martin , Vogeler Konrad 
Published: November 2013

This paper presents experimental investigations on flat plate film-cooling in combination with a ribbed cooling channel. The effect of rib placement on the film-cooling injection and the flow in the cooling channel was studied. The velocity fields were measured using optical laser measurement techniques as LDA (Laser-Doppler-Anemometry) and PIV (Particle-Image-Velocimetry). A row of three cylindrical film holes is placed in the center rib segment of the cooling channel. The dimensionless rib-to-hole position s/D is varied from 4.5 to 10.5. The investigations are conducted at isothermal conditions for a variation of the coolant Reynolds number Rec,Dh from 10000 up to 60000 and for three blowing rates M = 0.5, 0.75 and 1.00.
The flow field results for the film-cooling injection showed only small influence of the rib placement. Due to different coolant-to-main flow pressure ratios across the row, a slight non-uniform share of coolant flow occurs. Intense streamwise mixing and decay of the turbulence in the film jet was observed within the first 10 hole diameters. Enhancement of the turbulence intensity inside the jet core was found with increasing coolant Reynolds numbers.
Inside the internal cooling channel, the flow field showed significant influence of the rib position which is most pronounced at low Reynolds number (Rec,Dh = 10000) and high blowing ratios (M = 1.0). The effect becomes significantly smaller when the Reynolds number is increased. This is mainly attributed to the strongly increasing channel mass flow which equals to a decreasing suction ratio SR = uh/uc of the holes. The experimental results are compared to comprehensive numerical simulations.
Centrifugal Compressor Design Impacts: Lean and Meridional Shape
Authors: Xu Cheng , Amano R. S. 
Published: November 2013

Optimization procedures are widely used in centrifugal compressor developments to enable high efficiency and wide operating ranges of compressors. It is very important to understand how to set the parameters and which parameter needs to be optimized. This paper demonstrates a case study on the importance of mechanical and structure combination optimization and also discusses the meridional impacts of compressor performance.
Recently, the high pressure ratio and the efficiency of centrifugal compressors require impeller designs to pay attention to multi-disciplinary optimization. High efficiency and a wide operation range are always the design goal. The geometry of the blades and the meridional profile are very important contributors to compressor performance and structure reliability. Therefore, it is critical to consider all aspects of compressor optimization. The goal of currently used centrifugal compressors is to design a compressor with the same back-disc diameter with the best efficiency and the highest-pressure ratio.
Design and Development of a Specially Modified Positive Displacement Rotary Screw Pump and Relevant Hydraulic Circuit to Enhance “Entrained Air Handling” Capability in a Closed Loop Lube Oil System
Authors: Berti Simone , Fracassi Pietro , Mattioli Alessandra , Potula Varuna Reddy , Lotti Cristiano 
Published: November 2013

Rotary screw type positive displacement (RSPD) pumps are commonly used in Oil and Gas Industry for pumping of mineral lube oil in services where they can be mechanically driven by gears coupled to a train driver. Installation of these pumps is critical and should be designed jointly by vendors and users according to project specific restrictions (i.e. the arrangement of the entire oil circulation system). This paper describes a real case in which restrictions due to lube oil system arrangement have produced low pump suction head and have amplified the influence of air bubbles that remained entrained in oil despite lube oil tank degassing.
The investigations have been directed toward the mathematical modeling of the aeration phenomenon coupled with experimental measurements of critical parameters taken on the shop plant. Among corrective actions identified and considered there are reduction of quantity of air entering the lube oil system and revamping of the entire lube oil system with changes in piping, tank and also in pump model together with special modifications of internal path to enhance air handling capabilities. In order to validate pump behavior with reference to resistance to aeration (monitoring noise and vibration) a special simulation set-up was jointly developed by end user and manufacturer on a pilot test bench to carry out the various performance tests.
The numerical data collected during shop aeration test have confirmed that the pump was able to handle the expected amount of entrained air with noise and vibrations within industrial limits. The pumps tested in the pilot bench were installed at user’s site and the effectiveness of the synergic corrective actions listed above was successfully verified.
The study concludes that an early estimation of entrained air in the lube oil system is critical for design and development of either the RSPD pump or the entire lube oil circuit of a motor compressor train. When a critical quantity of entrained air is likely to be reached at pump suction (near 10% in volume), pump manufacturers and end users should apply some basic rules related to “design for aeration” of the pump and agree on a non-routine test to be performed at manufacturer’s shop before pump installation at site. This will serve as a reliable prediction of pump air handling capabilities, without which effective operation, reliability and durability of the pump could be jeopardized.
Numerical and Experimental Investigation of Tangential Endwall Contoured Blades in a 2-Stage Turbine
Authors: Schwab Stephan , Wendland Dominik , Wirsum Manfred 
Published: November 2013

This paper deals with the results of numerical and experimental investigations of tangential endwall contoured (TEWC) blades. The contouring is restricted to the blade passage and is implemented on the root and the shrouds for all blade rows. The investigated results of the new blade design have been compared to a reference blade design, which differs only in terms of the contouring. For this reason, the differences of the flow conditions can solely be attributed to the endwall contouring. All investigations have been carried out at different blade loadings in order to determine the potential improvement of the blading with respect to the efficiency.
The analysis has emphasized an efficiency improvement for the design point and an efficiency decrease for high blade loading. The under- and overturning are considered by means of the angle distributions behind the stages and serve as an indicator for the losses caused by the passage vortex. An attenuation of the passage vortex in the casing area resulting from the load relief in the casing-sided area can be observed. The contouring in the hub-area however leads to a higher development of the horseshoe vortex at high blade loading.
Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System
Authors: Liu Kexin , Martin Pete , Sanderson Victoria , Hubbard Phill 
Published: November 2013

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission (DLE) engine. Ignition, engine starting, emissions, combustion dynamics and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance.
Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9 and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio (AFR) at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas.
The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2 and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas).
Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design.
Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change.
Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.