bluuebunny/crossref_metadata_2025 huggingface dataset:
Ceramics Reliability: Statistical Analysis of Multiaxial Failure Using the Weibull Approach and the Multiaxial Elemental Strength Model
Authors: Lamon Jacques
Published: March 2015

Methodology for designing reliable ceramic components requires a precise evaluation and correlation of strengths in different stress states. The present paper compares the merits of the Weibull approach and the Multiaxial Elemental Strength model on an experimental case involving mixed mode failure in the presence of bimodal flaw populations (surface and volume flaws). The experimental data were obtained using flexure specimens of Si3N4 tested at various spans, with the purpose of enhancing shearing effects. The analysis of data was refined by developing an advanced post-processor program to finite element codes, for failure probability determination based upon the Barnett-Freudenthal approximation of the Weibull approach and the Multiaxial Elemental Strength Model. In a second step, the strengths of the specimens exhibiting failures from the two concurrent populations of flaws (intermediate span) were predicted using both approaches from data obtained with different span lengths (long and short spans). Comparison with experimental data showed that the Multiaxial Elemental Strength Model is an improvement over the Weibull approach. It also allowed the short span bending test to be assessed. Finally, important implications for structural design with ceramics are discussed.
A UK Perspective on Engine Health Monitoring (EHM) Systems for Future Technology Military Engines
Authors: Bairsto N. A.
Published: March 2015

The first part of the paper deals with the background to the UK experience in EHM. The programmes that have led to the UK’s experience are given and some lessons learnt are outlined which will be applied to Engine Health Monitoring (EHM) in future engines. The UK policy for the fleetwide fit of EHM equipment is stated. In the second part, the application of EHM to advanced technology engines is examined from a personal viewpoint. Future engines will include materials and aerothermal cycles that are in the research and development field. The impact of a structured approach to durability, the anticipated reduction of engine spares holdings and the requirement to improve flight safety and enhance engine availability are advanced as arguments in support of the development of EHM techniques alongside the development of future engines.
The Effects of Diffuser Geometry on Rotating Stall Behavior
Authors: Otugen M. V. , So R. M. C. , Hwang B. C.
Published: March 2015

Experiments were carried out in a model vaneless diffuser rig to investigate the rotating stall phenomenon and its relation to diffuser geometry. The experimental rig consisted of an actual impeller which was used to deliver the flow to the vaneless diffuser. Mass flow rate through the system could be adjusted by varying the rotational speed of the impeller at a fixed inlet opening or by changing the inlet opening at a fixed impeller speed. The flow exited to room condition. As such, the rig was designed to investigate the fluid mechanics of vaneless diffuser rotating stall only. Attention was focused on the effects of diffuser width and radius on rotating stall. Three diffuser widths and three outlet radii were examined. The width-to-inlet radius ratio varied between 0.09 and 0.142 while the outlet-to-inlet radius ratio varied between 1.5 and 2.

Results showed that the critical mass flow rate for the onset of rotating stall decreases with decreasing diffuser width. The critical mass flow rate is affected also by the diffuser radius ratio; larger radius ratios resulted in smaller critical mass flow rates. The ratio of the speed of rotation of the stall cell to impeller speed is found to decrease with increasing number of stall cells. This relative speed also decreases with increasing diffuser radius ratio, but it is largely independent of the diffuser width.
Active Magnetic Bearings for Gas Turbomachinery in Closed-Cycle Power Plant Systems
Authors: McDonald Colin F.
Published: March 2015

Bearing lubrication systems in closed-loop plants using gas (air or helium) as the working fluid (e.g., gas turbine, gas-cooled nuclear reactor, gas compressor, etc.) are very demanding since liquid lubricant ingress could contaminate the circuit, unlike open-cycle systems where the products would be expelled in the exhaust. Oil-lubricated bearings, the tribology mainstay in the power plant field, are reliable, but in the event of a failure in the seal or buffer system, the impact of oil ingress (e.g., saturation of insulation, coking on high-temperature surfaces, or in the extreme case, conflagration of equipment) can be costly and result in extended plant downtime.

The emergence in the early 1980s of a new tribology technology, namely a system in which the turbomachine rotor is levitated by a magnetic field, and positively sensed and controlled in real-time by an electronic system, now offers the designer an additional option. While an active magnetic system has many advantages, its foremost are (1) potential for very high reliability, (2) obviates the possibility of closed circuit contamination by lubricant ingress, (3) system simplicity, (4) ease of operation, and (5) ease of critical speed problems.

It is projected that utilization of “electronic chips instead of liquid films” will have a significant impact on the design of high-speed rotating machinery across the full spectrum of applications. This paper outlines the emergence of active magnetic bearings in rotating machinery for closed-cycle gas turbines, and in helium circulators for future high-temperature gas-cooled nuclear power plants. The paper highlights the existing industrial technology base that will make possible the deployment of active magnetic bearings in rotating machinery for the next generation of power plants that utilize closed-loop circuits.
The Influence of a Mainstream Thermal Boundary Layer on Film Effectiveness
Authors: Paxson D. E. , Mayle R. E.
Published: March 2015

A theoretical and experimental investigation on the effect of a mainstream thermal boundary layer on adiabatic film effectiveness is presented. The theory is based on a simple model which accounts for mixing between the the injected flow and a mainstream flow which has a viscous and thermal boundary layer. In order to apply this theory, the adiabatic film effectiveness in a flow with uniform temperature must be known either from experiments or from another theory. Experiments are described for an injection geometry having a simple two-dimensional slot. These tests were conducted with an insulated lip having a lip-diameter to slot-height ratio of 0.6. The mainstream thermal boundary layer was produced by heating the surface in contact with the mainstream flow upstream of the slot. Velocity and temperature distributions were measured at various distances downstream of the slot, along with measurements of the adiabatic wall temperatures. All tests were performed at a secondary to mainstream mass flux ratio of 0.7, but with different amounts of mainstream heating. While a comparison between theoretical and experimental results shows a discrepancy near injection, the trend is correct, and the agreement downstream is good.
Design Possibilities and Performance of Combined Cycle Operation of Converted Steam Power Plants
Authors: Linnemeijer M. J. J. , Van Buijtenen J. P.
Published: March 2015

An interesting method for “boosting thermal efficiency and/or power output of an existing steam power plant is repowering through the addition of gas turbines.

The forced draught fan is replaced by a gas turbine and the air heater by low-temperature economisers.

This conversion will change the performance of the installation significantly. Therefore the design of the existing installation has to be reviewed based on new unit performance calculations.

Since the conversion has to be economical, it is important to find a good compromise between investment and improvement of performance.

This paper describes the change in performance of the installation created by the conversion in general and a number of design possibilities based on the experience gained with the realisation of a number of conversion projects.

These projects show a possible efficiency increase of over 10% and a power increase of up to 30%.
Electron Microscopy Techniques for the Microstructural Characterization of Silicon Nitride
Authors: Siebein Kerry N. , Yeckley Russell L.
Published: March 2015

It is well known that the mechanical properties of ceramic materials are directly dependent upon their microstructure with respect to the size, crystallinity, distribution and composition of the phases present. Our understanding of the microstructural details of silicon nitride was enhanced through the application of scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM). The SEM and STEM are necessary for analyzing the microstructure of silicon nitride because it is a fine grained material. The SEM is used to analyze the etched microstructure and fracture surfaces of bulk silicon nitride samples. Relationships between the grain size distribution, aspect ratio of the grains and fracture toughness of the material are summarized, as well as fracture origin identity and bend strength data. STEM is employed to analyze the crystallinity, distribution and composition of the phases present in a material. These features are related to the processing parameters, fracture toughness and bend strength of silicon nitride. This paper presents a short description of the microscopy techniques employed to characterize silicon nitride, the results obtained using the various techniques and the relationship between the microstructural features and mechanical properties.
Investigation Into the Effect of Tip Clearance on Centrifugal Compressor Performance
Authors: Brasz Joost J.
Published: March 2015

The axial clearance between the tip of the blades of an unshrouded impeller and its stationary shroud has been varied to study its effect on overall compressor performance. The compressor under investigation consisted of an inlet nozzle, a 3D open impeller with full inducer, a parallel-wall vaneless diffuser and a collector. High-accuracy overall performance data were obtained for this compressor.

The experiments were carried out in a closed-loop centrifugal compressor test rig with the impeller running at a rotational Mach number u2/a0 = 1.39. The impeller tip diameter was 0.516 m, its tip width 0.021 m and the impeller blade exit angle was 30 degrees from radial.

Assuming a linear relationship, the experimental data indicates a pressure ratio decrease of 0.77 percent, an efficiency loss of 0.31 points, an input head reduction of about 0.25 percent and an output head reduction of about 0.65 percent for each percent increase in clearance ratio. However, the data seems to indicate a non-linear effect showing stronger performance sensitivity at smaller clearances.

The test data are compared against a clearance loss model. Improved performance prediction is obtained by including the effect of clearance on impeller work input.
Whisker Orientation Measurements in Injection Molded Si3N4-SiC Composites
Authors: Neil J. T. , Norris D. A.
Published: March 2015

Hot pressed composites of Si3N4 containing 30% SiC whiskers have shown substantial improvements in strength and fracture toughness relative to monolithic silicon nitride. Injection molded samples made of this composite material distorted in a systematic manner during densification by hot isostatic pressing. Whisker orientation and aspect ratio measurements based on digitized SEM micrographs were used to evaluate microstructure with respect to injection molding direction. Results show definite orientation of whiskers during injection molding which can be related to the observed densification distortion.
Decentralized Control and Automation of Gas Turbine and Combined-Cycle Power Plants
Authors: Bluhm Karl-Werner , Joyce John S. , Leemburg Anthoon
Published: March 2015

Unfired combined-cycle power plants of Siemens/KWU design each comprise five different package-engineered functional areas of mechanical and associated electrical equipment which are matched to different fuels, site conditions and operating requirements in order to achieve optimum power generation with each application. A modular programmable microprocessor-based automation station allocated to each functional area sequentially controls and protects all the equipment therein. By means of a redundant bus system all the functionally distributed automation stations are connected to one another and to a central control room where VDU screens provide operators with an in-depth insight into the running performance status of the entire combined-cycle block at all times. Function keyboards and back-up conventional hardwired controls permit operators to intervene in the automatic operation of the station whenever desired.
AGT 100 Project Summary
Authors: Helms H. E.
Published: March 2015

The Allison Gas Turbine Division of General Motors Corporation (GMC) completed the Advanced Gas Turbine Technology Project under contract to the National Aeronautics and Space Administration (NASA) Lewis Research Center (LeRC) using funding received from the Heat Engine Propulsion Division, Office of Transportation Systems in the Conservation and Renewable Energy Group of the Department of Energy (DOE) in the summer of 1987. This advanced, high risk work was initiated in the fall of 1979 under charter from the U. S. Congress to promote an engine for transportation that would provide an alternative to reciprocating spark-ignition (SI) engines for the U. S. automotive industry and simultaneously establish the feasibility of advanced ceramic materials for hot section components to be used in an automotive gas turbine (AGT).
Small Diameter Film Cooling Holes: Wall Convective Heat Transfer
Authors: Andrews G. E. , Alikhanizadeh M. , Asere A. A. , Hussain C. I. , Khoshkbar Azari M. S. , Mkpadi M. C.
Published: March 2015

The wall heat transfer resulting from small diameter holes drilled at 90° through gas turbine combustion chamber and turbine blade walls is considered. Available information is briefly reviewed and shown to generally omit the hole approach surface heat transfer and to relate only to the internal hole heat transfer. Experimental techniques are described for the determination of the overall heat transfer in a metal plate with a large number of coolant holes drilled at 90°. The results are compared with conventional short-tube internal heat transfer measurements and shown to involve much higher heat transfer rates and this mainly resulted from the additional hole approach flow heat transfer.
Numerical Correlation of Gas Turbine Combustor Ignition
Authors: Lee F. P. , Koblish T. , Marchionna N.
Published: March 2015

In single can combustor ignition tests, different results were obtained for pressure atomizing and airblast atomizing fuel injectors as well as for various ignition locations. In order to understand the effect of fuel spray characteristics and ignition locations on gas turbine combustion ignition characteristics, a computer simulation of fuel droplet ignition at engine starting flow conditions has been conducted. An ignition model for evaporating fuel droplets was incorporated with the numerical droplet tracking scheme in the computational flow field, which included a simulated ignition point source. A large number of various size droplets were computed for their trajectories and ignition reactions. A statistical data base was established to calculate the ignition probability of droplets in terms of number and mass fraction. A correlation between predicted ignition probability trends and experimental ignition data for two different injector/ignitor configurations was demonstrated.
Gas Turbine Application Over Thirty Years in a Middle East Oil Production Facility
Authors: Norris Patrick J. , Cunningham John
Published: March 2015

Kuwait Oil Company (KOC) has installed and operated gas turbines since 1957. There are currently 79 Gas Turbines ranging in size from 700 to 33,000 H.P. of various types, from industrial to aero-derivative.

Gas turbines provide more than half a million in horsepower, which is more than 80% of the power, for machinery and power generation at KOC.

This paper covers the introduction and the rappid growth of gas turbine power at KOC. Operational sites at KOC are subject to severe heat, dust and humidity. The experience in the operation and maintenance in the early years of the gas turbines at KOC are described.

Gas turbines have played a major role in the success of the Company.
Numerical Integration of the 3D Unsteady Euler Equations for Flutter Analysis of Axial Flow Compressors
Authors: Gerolymos G. A.
Published: March 2015

In order to analyze axial-flow compressor flutter, methods are required that compute the unsteady flow through vibrating cascades. A 3D fully nonlinear method has been developed by numerically integrating the 3D unsteady Euler equations, in the time-domain. The equations are discretized in a moving grid, which conforms with the vibrating blades and are integrated using the explicit MacCormack scheme, in finite-difference formulation. The method assumes a traveling-wave assembly mode of vibration. In this manner, the flow is computed in a single channel by applying the corresponding chorochronical periodicity condition at the permeable pitchwise limits. The blade vibratory mode is an input to the method obtained by a standard finite element method structural analysis code. A number of results are presented, for a transonic fan rotor, illustrating the possibilities of the method, both in started and unstarted supersonic flow conditions.
Full Coverage Impingement Heat Transfer: Cooling Effectiveness
Authors: Abdul Husain R. A. A. , Andrews G. E. , Asere A. A. , Ndiema C. K. W.
Published: March 2015

Cooling effectiveness data are presented for impingement cooled surfaces with no film cooling and the results are directly compared with both effusion film and combined impingement/effusion cooling. The aim was to evaluate the potential of optimised impingement cooling designs to adequately cool combustor wall and turbine blade surfaces. Specific designs relevant to a combustor wall cooling application were investigated, and in particular the situation where all the combustor air flow was used for wall cooling prior to combustion. This requires the impingement pressure loss to be minimised so that an adequate pressure loss remains for the combustion process. Consequently, the impingement plate pressure loss or X/D was the major parameter investigated for a fixed number of holes of 4306/m2. It was shown that a high cooling effectiveness was achieved with a low pressure loss, thus establishing total impingement cooled combustors as a viable design possibly removing any requirement for the present large combustor film cooling flows.
Development of Ceramic Turbine Rotors
Authors: Katayama K. , Sasaki M. , Itoh T.
Published: March 2015

A ceramic gas turbine engine is one of the most promising candidates for future automotive engines. Among the different ceramic components required to build such an engine, the turbine rotor is thought to be the most difficult to fabricate with ceramics. This is because the rotor has a very complex shape and is subjected to high stress.

This paper describes reliability evaluations of ceramic radial turbine rotors for a gas turbine engine and for a turbocharger. Each rotor was analyzed using a probabilistic approach. This included the use of finite element analysis, Weibull’s distribution function for brittle materials and lifetime predictions based on slow crack growth. The influence of blade thickness on foreign particle damage to a ceramic rotor is also discussed.

The results of these evaluations led to the design and development of a highly reliable turbocharger rotor, which has been used since October 1985 in Nissan passenger cars sold in the domestic market.
Increasing the Capacity Factors of Base Load Generating Facilities by Storage of Electrical Energy in Aquifers as Compressed Air
Authors: Longardner Robert L. , Visnesky Anthony , Strother J. R.
Published: March 2015

This paper sets out the advantages of using “off-the-shelf” equipment to produce an effective Compressed Air Energy System (CAES) and to develop the storage parameters of those geological entrapments that can be pressurized with air for the generation of electrical energy on demand.

The long lead time and the developmental cost needed to perfect turbo-machinery for aquifer storage has been a deterrant on the utilities in their desire to implement air storage in aquifers. Off-the-shelf hardware and predesigned turbo-machinery specified herein is readily adaptable to aquifer storage parameters and can be manufactured without the expense and uncertainty related to developmental hardware. Hence, normal equipment manufacturer’s assurances and guarantees are available for these applications.

When compared to the alternative storage opportunities such as; pumped hydro, battery storage and superconducting magnetic storage, the cost of compressed air storage in aquifers is a fraction of the first cost of these alternatives and as good or better in operating costs.
Turbomachinery Alloys Affected by Solid Particles
Authors: Tabakoff W.
Published: March 2015

In operating gas turbine engines in dusty environments, severe erosion of compressor and turbine components results. This erosion adversely effects engine performance. Predicting erosion in the rotating machine of gas turbine is a complex problem. This paper presents test data from the high temperature material erosion facility at the University of Cincinnati. Data was obtained between a target temperature of ambient and 649°C (1200°F) for AM355, Rene 41 and L605 cobalt. In addition, particle velocity and impingement angle were varied.
Competitive Acquisition: What Makes Sense for Engines?
Authors: Coalson Michael S.
Published: March 2015

Acquisition of aeronautical gas turbine engines is a very critical and very expensive aspect of weapon system procurement. The Air Force uses various acquisition strategies in developing and procuring new engines which have the intent of reducing cost in both buying and operating engines. One of those strategies is the fostering of competition. The topic of this paper is to review various opportunities for fostering competition and to describe areas, other than the obvious one of initial cost, where a responsive contractor can enhance his competitive position. We will consider only opportunities for competition at the prime contractor level; vendor and spares competition are left for other papers.
An Investigation of Axial Pump Backflow and a Method for its Control
Authors: Abramian M. , Howard J. H. G. , Hermann P.
Published: March 2015

The flow field within an axial flow inducer pump near the blade leading edge was explored by laser-Doppler velocimetry to extend the previous studies of the recirculation zone which is observed at low flow rates. Although a considerable region of upstream reverse flow and swirl was observed, the recirculation zone within the impeller was of limited axial extent and was confined to the pressure side of the passage. In an attempt to reduce the flow reversal, a series of perforated disks were placed in front of the inducer. The optimum disk geometry produced minor changes in the pump performance. LDV measurements of the flow field ahead and behind the disk showed considerable reduction of the swirl velocity under reverse flow conditions, with the observed upstream swirl opposite to the inducer rotation.
How to Achieve Strain Tolerant Thermal Barrier Coatings (TBC’s) by Means of Varying Spray Parameters
Authors: Johner G. , Wilms V. , Schweitzer K. K.
Published: March 2015

Small gas turbine engines, especially if they are used as automotive propulsion systems, are often compared to diesel engines with regard to their specific fuel consumption. Aside from high gas temperatures and the use of very efficient heat exchangers, there has to be a form of thermal insulation of the turbine casing which can be achieved by means of a thick Thermal Barrier Coating (TBC).

Theoretical considerations about the necessary morphology are made on the calculated stress situation within the coating. It will be described, how the TBC morphology can be influenced as desired, by means of a specific selection of spray parameters. In addition, the correlation between spray parameters and the phase distribution, as obtained from neutron diffraction analyses, will be reported.

The compatibility between theory and practice will be proven by means of a turbine case dummy with an inner TBC with a thickness of 5 mm which was tested very realistically in a specially designed flame rig. Microsections of this coating are used to confirm the theoretical considerations of the necessary morphology.
Temperature Rise in the Multistage Axial Flow Compressor During Rotating Stall and Surge
Authors: Nácovská Katerina
Published: March 2015

An experimental investigation of rotating stall and surge was carried out on a four stage axial flow compressor. Results of flow and blade temperature measurements in the compressor are presented. Internal temperature levels during rotating stall and surge are considerably higher than those obtained during unstalled compressor operation. In the pure rotating stall regime, the temperature is almost identical in all compressor stages and depends only on rotor speed and mass flow rate. During surge, the highest temperature is found at the tip diameter prior to the first stage rotor. The absolute level depends on rotor speed, mass flow rate (i.e. throttle position) and on the number of compressor stages. A model of the temperature changes in the multistage compressor during the surge cycle has been derived from the experiments.
Laminar Flow Velocity and Temperature Distributions Between Coaxial Rotating Disks of Finite Radius
Authors: Orletsky D. T. , Louis J. F.
Published: March 2015

Predictions of the laminar flow and temperature distribution between coaxial rotating disks of finite radius have been obtained using a computer model solving the Navier-Stokes equation for a laminar fluid of constant properties. To do this, a stream vorticity model in the r-z plane is used in the solution of the Navier-Stokes equation. The velocity fields were obtained for both shrouded and unshrouded disks with or without radial throughflow for either co-rotating or counter-rotating disks. Velocity profiles predicted by this model were compared to experimental data, to a similarity solution and to a large aspect ratio model. The results obtained by this model closely matched the experimental data, and the large aspect ratio solution for the cases considered. The uncoupled energy equation was then solved using the calculated velocity distribution for the temperature distribution between the disks. This was done for two cases: i) two isothermal disks, and ii) one isothermal disk and one adiabatic disk.
Prediction of the Pressure Distribution for Radial Inflow Between Co-Rotating Discs
Authors: Chew John W. , Snell Robert J.
Published: March 2015

The problem of radial inflow between two plane co-rotating discs with the angular velocity of the fluid at inlet equal to that of the discs is considered. An integral solution technique for turbulent flow, based on that of von Karman (1921), is described. Solutions are shown to be in good agreement with most of the available experimental data. For incompressible flow the pressure drop coefficient is a function of just two non-dimensional parameters; the radius ratio for the cavity and a throughflow parameter. For air flows compressibility can be important and an additional non-dimensional parameter is needed. Results for a wide range of conditions are presented graphically. These show the sensitivity of the pressure coefficient to the governing parameters and provide a quick method for estimating the pressure drop.
Total Corrosion Control for Industrial Gas Turbines: Airborne Contaminants and Their Impact on Air/Fuel/Water Management
Authors: Hsu L. L.
Published: March 2015

Turbine longevity in the field is determined by the extent of its operation within design limits under mechanical and thermal loads as well as the environmental effects that undermine material properties on component surfaces. It is standard practice for the original equipment manufacturer (OEM) to specify maximum concentrations of harmful contaminants in the fuel for corrosion control. Some manufacturers have deployed on-line, in-service monitoring systems designed to incorporate data, such as temperature, speeds and start-stop cycles, into a functional, quasi-empirical equation, with an environmental factor, to continuously assess the condition of the turbine package for maintenance and overhaul purposes. This environmental factor simply categorizes fuel types in some generic correlation of fuel with hot section degradation.

This paper discusses the concept of air, fuel and water management, an approach that has evolved at the author’s Company as a focused and cost-effective means of assessing the total turbomachinery environment. The ultimate objective is to employ the methodology described above for hot section corrosion life prediction and optimized maintenance planning with minimal capitalization and operating costs for maximum economic payback.

The fundamental principle of this approach is represented schematically in Fig. 1 and discussed in more detail in Ref. 1. For total corrosion control, the engine environment is the sum of all contaminants present in the air, fuel and water (or steam). Tradeoffs in fluid quality can be tolerated provided the combined total concentration of a critical contaminant does not exceed the maximum allowable limits. Instead of separate restrictions on air, fuel and water quality, combined limits on total concentrations should be defined which then allows each fluid to vary in quality, thus providing greater flexibility for accommodating customer requirements or site specific conditions.
Development of a 3D Navier Stokes Solver for Application to all Types of Turbomachinery
Authors: Dawes W. N.
Published: March 2015

This paper describes the current stage of development of a code aimed at solving the 3D Navier-Stokes equations in any type of turbomachinery geometry. The basic algorithm time marches the fully 3D unsteady equations of motion expressed in finite volume form with a two step explicit / one step implicit method. Full multigrid acceleration is used to reduce solution time and maintain code performance on fine meshes. Turbulence modelling is via mixing-length closure and the widely used Baldwin-Lomax model.

The generality and robustness of the code is demonstrated by application to five different test cases, three axial and two radial configurations. Also included is a grid independence study which demonstrates near grid independent solutions for transonic compressor cascade flow (albeit with the actual result subject to transition modelling constraints).

For two of the axial cases (transonic compressor in cascade, secondary flow in a high speed compressor) and one radial case (Eckardt high speed impellor) sufficient mesh is employed for the predictions to be essentially quantitative. The other two cases (radial inflow turbine with clearance and compressor stator with hub clearance) are really simulations rather than predictions, but are included as the flows are novel and provide much physical insight.
Effects of CT‐based attenuation correction of rat microSPECT images on relative myocardial perfusion and quantitative tracer uptake
Authors: Strydhorst Jared H. , Ruddy Terrence D. , Wells R. Glenn
Published: March 2015

Purpose:

Our goal in this work was to investigate the impact of CT‐based attenuation correction on measurements of rat myocardial perfusion with 99mTc and 201Tl single photon emission computed tomography (SPECT).

Methods:

Eight male Sprague‐Dawley rats were injected with 99mTc‐tetrofosmin and scanned in a small animal pinhole SPECT/CT scanner. Scans were repeated weekly over a period of 5 weeks. Eight additional rats were injected with 201Tl and also scanned following a similar protocol. The images were reconstructed with and without attenuation correction, and the relative perfusion was analyzed with the commercial cardiac analysis software. The absolute uptake of 99mTc in the heart was also quantified with and without attenuation correction.

Results:

For 99mTc imaging, relative segmental perfusion changed by up to +2.1%/−1.8% as a result of attenuation correction. Relative changes of +3.6%/−1.0% were observed for the 201Tl images. Interscan and inter‐rat reproducibilities of relative segmental perfusion were 2.7% and 3.9%, respectively, for the uncorrected 99mTc scans, and 3.6% and 4.3%, respectively, for the 201Tl scans, and were not significantly affected by attenuation correction for either tracer. Attenuation correction also significantly increased the measured absolute uptake of tetrofosmin and significantly altered the relationship between the rat weight and tracer uptake.

Conclusions:

Our results show that attenuation correction has a small but statistically significant impact on the relative perfusion measurements in some segments of the heart and does not adversely affect reproducibility. Attenuation correction had a small but statistically significant impact on measured absolute tracer uptake.
Watching harmonics beat
Authors: Keeports David
Published: March 2015

Suppose you record a song on magnetic tape and duplicate your recording. You then simultaneously play back both tapes. To the rim of one of the tape reels, also known as the reel's flange, you keep applying gentle pressure and then releasing that pressure so that your reel alternates between slightly lagging the other and then catching up with it. The resulting small pitch differences between the two tapes give rise to an intriguing and pleasant sound often described as swirling or jet-like. A Wikipedia article1 lists dozens of popular songs that incorporate this “flanging” effect. Well represented are songs by the Beatles and Jimi Hendrix as well as by artists from recent decades. But perhaps the most important is an obscure 1945 recording by guitarist and musical inventor Les Paul, who is recognized as the discoverer of flanging.
Contextual plasticity, top-down, and non-auditory factors in sound localization with a distractor
Authors: Kopčo Norbert , Marcinek Ľuboš , Tomoriová Beáta , Hládek Ľuboš
Published: March 2015

Localization of a 2-ms-click target was previously shown to be influenced by interleaved localization trials in which the target was preceded by an identical distractor [Kopčo, Best, and Shinn-Cunningham (2007). J. Acoust. Soc. Am. 121, 420–432]. Here, two experiments were conducted to explore this contextual effect. Results show that context-related bias is not eliminated (1) when the response method is changed so that vision is available or that no hand-pointing is required; or (2) when the distractor-target order is reversed. Additionally, a keyboard-based localization response method is introduced and shown to be more accurate than traditional pointer-based methods.
A comparison of spectral estimation methods for the analysis of sibilant fricatives
Authors: Reidy Patrick F.
Published: March 2015

It has been argued that, to ensure accurate spectral feature estimates for sibilants, the spectral estimation method should include a low-variance spectral estimator; however, no empirical evaluation of estimation methods in terms of feature estimates has been given. The spectra of /s/ and /ʃ/ were estimated with different methods that varied the pre-emphasis filter and estimator. These methods were evaluated in terms of effects on two features (centroid and degree of sibilance) and on the detection of four linguistic contrasts within these features. Estimation method affected the spectral features but none of the tested linguistic contrasts.
Understanding Dignity: Experiences of Impairment in an Exercise Facility
Authors: Johnston Keith R. , Goodwin Donna L. , Leo Jennifer
Published: March 2015

Dignity, as an essential quality of being human, has been overlooked in exercise contexts. The aim of this interpretative phenomenological study was to understand the meaning of dignity and its importance to exercise participation. The experiences of 21 adults (11 women and 10 men) from 19 to 65 yr of age who experience disability, who attended a specialized community exercise facility, were gathered using the methods of focus-group and one-on-one interviews, visual images, and field notes. The thematic analysis revealed 4 themes: the comfort of feeling welcome, perceptions of otherness, negotiating public spaces, and lost autonomy. Dignity was subjectively understood and nurtured through the respect of others. Indignities occurred when enacted social and cultural norms brought dignity to consciousness through humiliation or removal of autonomy. The specialized exercise environment promoted self-worth and positive self-beliefs through shared life experiences and a norm of respect.
Nonabelian holomorphic Lie algebroid extensions
Authors: Bruzzo Ugo , Mencattini Igor , Rubtsov Vladimir N. , Tortella Pietro
Published: March 2015

We classify nonabelian extensions of Lie algebroids in the holomorphic category. Moreover we study a spectral sequence associated to any such extension. This spectral sequence generalizes the Hochschild–Serre spectral sequence for Lie algebras to the holomorphic Lie algebroid setting. As an application, we show that the hypercohomology of the Atiyah algebroid of a line bundle has a natural Hodge structure.
GENERALIZED WEIERSTRASS–MANDELBROT FUNCTION MODEL FOR ACTUAL STOCKS MARKETS INDEXES WITH NONLINEAR CHARACTERISTICS
Authors: ZHANG L. , YU C. , SUN J. Q.
Published: March 2015

It is difficult to simulate the dynamical behavior of actual financial markets indexes effectively, especially when they have nonlinear characteristics. So it is significant to propose a mathematical model with these characteristics. In this paper, we investigate a generalized Weierstrass–Mandelbrot function (WMF) model with two nonlinear characteristics: fractal dimension D where 2 > D > 1.5 and Hurst exponent (H) where 1 > H > 0.5 firstly. And then we study the dynamical behavior of H for WMF as D and the spectrum of the time series γ change in three-dimensional space, respectively. Because WMF and the actual stock market indexes have two common features: fractal behavior using fractal dimension and long memory effect by Hurst exponent, we study the relationship between WMF and the actual stock market indexes. We choose a random value of γ and fixed value of D for WMF to simulate the S&P 500 indexes at different time ranges. As shown in the simulation results of three-dimensional space, we find that γ is important in WMF model and different γ may have the same effect for the nonlinearity of WMF. Then we calculate the skewness and kurtosis of actual Daily S&P 500 index in different time ranges which can be used to choose the value of γ. Based on these results, we choose appropriate γ, D and initial value into WMF to simulate Daily S&P 500 indexes. Using the fit line method in two-dimensional space for the simulated values, we find that the generalized WMF model is effective for simulating different actual stock market indexes in different time ranges. It may be useful for understanding the dynamical behavior of many different financial markets.
Penny-Shaped Crack in a Poroelastic Plate
Authors: Gilbert Robert P. , Lee Doo-Sun
Published: March 2015

Hydraulic fracking is used in the petroleum industry for the secondary production of either oil or natural gas. Normally a high pressure fluid is injected through a well bore to create cracks or fissures in the oil bearing sediment. Usually small grains of sand are suspended in the fracking fluid and remain after the pressure is released; thereby, allowing the oil or gas to pass more freely through the fissure. Because of the large difference of permeability of the fissure to the oil bearing strata, oil or gas flows easily into the fissure and is easily produced through the well bore. In our model we consider the fractured vein to be approximated by a penny-shaped crack, placed horizontal to the well bore. Because of symmetry conditions, in the case of a gravity drainage model for producing oil, a crack lying at the bottom of the oil bearing strata can be modeled by a sediment of twice that size with a crack lying in the center. For the case of producing natural gas a similar argument may be made. What is of interest to the petroleum industry is to determine the size of the fracture, in our case that would be the radius. This problem may be reformulated as an inverse problem where we attempt to find the radius of the fracture from sonic information, for example, by measuring the scattered Lamb waves which are created by a suddenly imposed stress on the fracture. In the present work we consider the direct problem, namely what are the amplitudes of the scattered wave for known penny-shaped crack. In a subsequent paper we will consider the inversion of the Lamb wave data to reveal the radius of the fissure.
Synthesis of carboxylated chlorophylls and their application as functional materials
Authors: Sasaki Shin-ichi , Wang Xiao-Feng , Ikeuchi Toshitaka , Tamiaki Hitoshi
Published: March 2015

A series of chlorophyll derivatives possessing a carboxy group were synthesized aiming at their application as sensing materials and to dye-sensitized solar cells (DSSCs). Their absorption and fluorescence responses to amine concentrations in THF and photovoltaic performance of DSSCs on TiO 2 films were investigated.
A Note on Boolean Stochastic Processes
Authors: Fidaleo Francesco
Published: March 2015

For the quantum stochastic processes generated by the Boolean commutation relations, we prove the following version of De Finetti Theorem: each of such Boolean processes is exchangeable if and only if it is independent and identically distributed with respect to the tail algebra.
State of the Art of Fuzzy Methods for Gene Regulatory Networks Inference
Authors: Al Qazlan Tuqyah Abdullah , Hamdi-Cherif Aboubekeur , Kara-Mohamed Chafia
Published: March 2015

To address one of the most challenging issues at the cellular level, this paper surveys the fuzzy methods used in gene regulatory networks (GRNs) inference. GRNs represent causal relationships between genes that have a direct influence, trough protein production, on the life and the development of living organisms and provide a useful contribution to the understanding of the cellular functions as well as the mechanisms of diseases. Fuzzy systems are based on handling imprecise knowledge, such as biological information. They provide viable computational tools for inferring GRNs from gene expression data, thus contributing to the discovery of gene interactions responsible for specific diseases and/or ad hoc correcting therapies. Increasing computational power and high throughput technologies have provided powerful means to manage these challenging digital ecosystems at different levels from cell to society globally. The main aim of this paper is to report, present, and discuss the main contributions of this multidisciplinary field in a coherent and structured framework.
A Fuzzy Multiobjective Model for Supplier Selection under Considering Stochastic Demand in a Supply Chain
Authors: Pan Wei , Wang Fengxia , Guo Ying , Liu Shan
Published: March 2015

With the development of market competition, company faces more and more pressures. Meanwhile, procurement has a vital effect on achieving competitive advantages in a supply chain. Selecting the appropriate suppliers is one of the most important sections in purchase management. However, in real situation, supplier selection is a multiple objective problem about different items with vagueness and randomness of the data. It is very complex. Hence, research about supplier selection is relatively scarce under considering multiple items, discount price, and fuzzy and stochastic information. In our paper, we develop a fuzzy multiobjective supplier selection model for overcoming uncertainty and multiple items. Stochastic demand, fuzzy objectives, and weights are simultaneously applied to help the managers to select the suitable suppliers about different items. For illustration purpose, a numerical example is presented to verify the effectiveness of the proposed model.
Optimization on Preparation Conditions of Salidroside Liposome and Its Immunological Activity on PCV-2 in Mice
Authors: Feng Yibo , Zhao Xiaojuan , Lv Fang , Zhang Jinqiu , Deng Bihua , Zhao Yanhong , Hu Yuanliang , Wang Deyun , Liu Jiaguo , Lu Yu , Bo Ruonan , Liu Zhenguang
Published: March 2015

The aim of this study was to optimize the preparation conditions of salidroside liposome with high encapsulation efficiency (EE) and to study the immunological enhancement activity of salidroside liposome as porcine circovirus type 2 virus (PCV-2) vaccine adjuvant. Response surface methodology (RSM) was selected to optimize the conditions for the preparation of salidroside liposome using Design-Expert V8.0.6 software. Three kinds of salidroside liposome adjuvants were prepared to study their adjuvant activity. BALB/c mice were immunized with PCV-2 encapsulated in different kinds of salidroside liposome adjuvants. The PCV-2-specific IgG in immunized mice serum was determined with ELISA. The results showed that when the concentration of ammonium sulfate was 0.26 mol·L−1, ethanol volume 6.5 mL, temperature 43°C, ethanol injection rate 3 mL·min−1, and salidroside liposome could be prepared with high encapsulation efficiency of 94.527%. Salidroside liposome as adjuvant could rapidly induce the production of PCV-2-specific IgG and salidroside liposome I adjuvant proved to provide the best effect among the three kinds of salidroside liposome adjuvants.
Kernel Method Based Human Model for Enhancing Interactive Evolutionary Optimization
Authors: Pei Yan , Zhao Qiangfu , Liu Yong
Published: March 2015

A fitness landscape presents the relationship
between individual and its reproductive success in evolutionary
computation (EC). However, discrete and approximate
landscape in an original search space may
not support enough and accurate information for EC
search, especially in interactive EC (IEC). The fitness
landscape of human subjective evaluation in IEC is very
difficult and impossible to model, even with a hypothesis
of what its definition might be. In this paper, we
propose a method to establish a human model in projected
high dimensional search space by kernel classification
for enhancing IEC search. Because bivalent logic
is a simplest perceptual paradigm, the human model
is established by considering this paradigm principle.
In feature space, we design a linear classifier as a human
model to obtain user preference knowledge, which
cannot be supported linearly in original discrete search
space. The human model is established by this method
for predicting potential perceptual knowledge of human.
With the human model, we design an evolution
control method to enhance IEC search. From experimental
evaluation results with a pseudo‐IEC user, our proposed model and method can enhance IEC search
significantly.
Characterization of the Oxides Present in a Polydimethylsiloxane Layer Obtained by Polymerisation of Its Liquid Precursor in Corona Discharge
Authors: Groza A. , Surmeian A.
Published: March 2015

By combining the reflection‐absorption infrared spectral studies with the peak fitting analysis we determined the type of the silicon oxides present in polydimethylsiloxane layers obtained on germanium and aluminium substrates in corona discharges. We have also evidenced that the dependence of silicon oxides density on the corona discharge current intensity is related to the existence of a concurrent anodizing process occurring at the polymer/Al substrate interface. The morphology of the Al substrate surface investigated by scanning electron microscopy proved that the anodizing process occurs.