bluuebunny/crossref_metadata_2025 huggingface dataset:
An Experimental Study for Fatigue Performance of 7% Nickel Steels for Type B Liquefied Natural Gas Carriers
Authors: Kim Young Woo , Jin Oh Dong , Lee Jae Myung , Noh Byeong Jae , Sung Hee Joon , Ando Ryuichi , Matsumoto Toshiyuki , Hyun Kim Myung
Published: February 2016

Structural safety is one of the most important issues associated with liquefied natural gas (LNG) storage systems, such as LNG carriers, LNG Floating Production Storage Offloading (FPSO), and Floating Storage Regasification Unit (FSRU). One of the most common materials for the LNG storage systems has been 9% nickel steel over the last 50 years as it has excellent mechanical properties under cryogenic temperature. Recently, there have been efforts for lowering the nickel content due to the increased nickel price as well as the high price of nickel based welding consumables. In this respect, 7% nickel steels are recently developed for reducing the associated costs mainly for cryogenic applications. The newly developed 7% nickel steels are known to have improved toughness comparable to that of 9% nickel steels by thermomechanical control process (TMCP) and micro-alloying technology. The main objective of this study is to evaluate the fatigue performance of 7% nickel steels with a special attention to type B LNG carrier applications. Cyclic fatigue and fatigue crack growth rate (FCGR) tests for 7% nickel steels were conducted at room and cryogenic temperatures. Fatigue tests were carried out with three different types of specimens such as base metal, butt weld, and fillet weld to characterize the fatigue properties at various locations. In addition, FCGR tests were carried out using compact tension (C(T)) specimens. The difference of FCGR characteristics among base, weld, and heat affected zone (HAZ) is investigated. The fatigue and FCGR test results of 7% nickel steels are evaluated and compared with reference data of 9% nickel steel. Based on this study, it is observed that the 7% nickel steel exhibits similar fatigue performance in comparison with that of 9% nickel steel.
Predicting Dimensions of a Rectangular Fin Satisfying a Given Internal Heat Generation Using Inverse Method
Authors: Das Ranjan
Published: February 2016

This paper deals with a computational study to predict important dimensions of a rectangular fin used in gas turbine blade cooling for satisfying a prescribed internal heat generation. The heat transfer is assumed to occur by simultaneous conduction, convection and radiation. The effect of temperature-dependent thermal conductivity has been also taken into consideration. Rectangular fin geometry has been considered due to its simplicity and easiness of fabrication. Corresponding to known values of various thermo-physical parameters, at first using the fourth order implicit Runge-Kutta-based forward method, the relevant steady-state temperature distribution is evaluated. Forward method has been well-validated with three numerical schemes and experimental data. Thereafter, an inverse problem is solved using the genetic algorithm (GA) for predicting fin dimensions satisfying a prescribed temperature distribution corresponding to a fixed internal heat generation. The relevant objective function has been formulated using a three-point error minimization technique represented by square of residuals between guessed and available temperature distributions. The analysis has been done for three different fin materials such as Inconel, Hastelloy and Titanium. These materials are generally used in gas turbine blade applications due to their high melting point along with good fatigue, corrosion and creep properties. Effects of random measurement errors following a Gaussian profile are analyzed. The variations of relevant parameters are studied at different generations of GA. It is observed that for a given fin material, many feasible dimensions can sustain a given amount of internal heat generation which offer sufficient scopes to the fin designer. For the required amount of heat generation, the suitability of estimated parameters has been verified by the comparison between actual and reconstructed temperature distributions alongwith minimization of total fin volume. The present work is proposed to be useful in selecting appropriate dimensional fin configurations corresponding to a given material which can satisfy a fixed amount of internal heat generation.
Effect of Downstream Contraction on Liner Heat Transfer in a Gas Turbine Combustor Swirl Flow
Authors: Kedukodi Sandeep , Ekkad Srinath
Published: February 2016

Established numerical approaches for performing detailed flow analysis happens to be an effective tool for industry based applied research. In the present study, computations are performed on multiple gas turbine combustor geometries for turbulent, non-reactive and reactive swirling flow conditions for an industrial swirler. The purpose of this study is to identify the location of peak convective heat transfer along the combustor liner under swirling inlet flow conditions and to investigate the influence of combustor geometry on the flow field. Instead of modeling the actual swirler along with the combustor, an inlet swirl flow profile is applied at the inlet boundary based on previous literature. Initially, the computed results are validated against available experimental data for an inlet Reynolds number flow of 50000 using a 2D axi-symmetric flow domain for non-reacting conditions. A constant heat flux on the liner is applied for the study. Two turbulence models (RNG k-ε and k-ω SST) are utilized for the analysis based on its capability to simulate swirling flows. It is found that both models predict the peak liner heat transfer location similar to experiments. However, k-ε RNG model predicts heat transfer magnitude much closer to the experimental values except displaying an additional peak whereas k-ω model predicts only one peak but tends to over-predict in magnitude. Since the overall characteristic liner heat transfer trend is captured well by the latter one, it is chosen for future computations. A 3D sector (30°) model results also show similar trends as 2D studies. Simulations are then extended to 3 different combustors (Case 1: full cylinder and Case 2 and 3: cylinders with downstream contractions having reduced exit areas) by adopting the same methodology for same inlet flow conditions. Non-reacting simulations predict that the peak heat transfer location is marginally reduced by the downstream contraction of the combustor. However the peak location shifts towards downstream due to the presence of accelerated flow.

Reacting flow simulations are performed with Flamelet Generation Manifold (FGM) model for simulating premixed combustion for the same inlet flow conditions as above. It is observed that Case 3 predicts a threefold increase in the exit flow velocity in comparison to non-reacting flow simulations. The liner heat transfer predictions show that both geometries predict similar peak temperatures. However, only one fourth of the initial liner length experiences peak temperature for Case 1 whereas the latter continues to feel the peak till the end. This behavior of Case 3 can be attributed to rapid convection of high temperature products downstream due to the prevailing accelerated flow.
Stall Margin Improvement of a Single Stage Transonic Axial Flow Compressor Using Naturally Aspirated Slots
Authors: Borra Hari Krishna , Alone Dilipkumar Bhanudasji
Published: February 2016

This paper describes the method to improve the stall margin of transonic axial flow compressor by controlling the boundary layer on the suction surface of the rotor blade tip through natural aspiration. Aspiration slots in the compressor blade are intended to energize the flow by increasing its momentum on the suction surface. This phenomenon of boundary layer control can delay the flow separation and hence results in enhancement of the stall margin of the compressor stage. Flow behavior with aspiration slots and its performance are evaluated using commercially available numerical software. Steady state RANS simulations with three dimensional implicit pressure-based coupled solver and turbulence model SST k-ω are used.

The effect of natural aspiration slot on the rotor blade performance is computed numerically. The main objective of the study was to identify the optimum location of the aspiration slot along the chord of the compressor on the rotor blade. The axial location chosen for the performance evaluations were 20%,40%,50%,60% and 70% of the rotor blade axial tip chord. By comparing the numerical simulation results with the steady state behavior in the absence of the aspirated slots, the optimized location of the aspiration slot that results in maximum stall improvement is identified. At the optimized location, natural aspiration slots on the rotor blade tip improved the stall margin with the minimum reduction in efficiency and stage pressure ratio when compared to base model. After critically understanding the performance with straight aspiration slots the compressor stage performance has enhanced further by orienting the aspiration slots. The numerical three dimensional results conclude an optimal improvement in the stall margin for the slots near the trailing edge of the rotor. The prediction shows that with the inclined aspiration slots at proper location it is possible to improve the stall margin of the compressor stage and also to restore the stage efficiency.
On Site Testing of a Zero Head Vertical Axis Helical Water Turbine for Power Generation
Authors: Talukdar Parag K. , Kumar Sarbindu , Kulkarni Vinayak , Das Amarendra K. , Saha Ujjwal K.
Published: February 2016

The need of an efficient, low cost and environment friendly hydraulic energy converter provides motivation to many researchers to contribute in the field of renewable energy. In the present investigation, one such requirement is addressed for the possibility of electrical power generation from free stream of water. The implementation of such a low head or zero head turbine does not require a dam for energy conversion, thereby making it a low cost and environmental friendly source of power generation. The present study deals with the development of a zero head vertical-axis helical water turbine, and its subsequent testing in an open channel. The main parameters that influence the performance of a helical water turbine are its blade profile, aspect ratio, helix angle, number of blades and solidity ratio. Considering these parameters and the numerical work reported in literature, a three-bladed helical turbine has been developed and tested under different loading conditions. The variation of power coefficient at various tip-speed ratios of the turbine has been investigated and analyzed.
Flow Behavior in a Transonic Axial Compressor Stage
Authors: Kumar S. Satish , Ganguli Ranjan , Kandagal S. B. , Jana Soumendu
Published: February 2016

The steady and unsteady flow characteristics typically vary along and across the axial compressor stage. This coupled with asymmetric rotor tip clearance that occurs in practice makes flow even more complex. Understanding the complex flow behavior inside the transonic compressor stage will aid in developing flow control devices that are meant for purposes such as improving the rotating stall margin, flutter margin, etc. Here, a detailed time averaged numerical analysis is performed on the single stage transonic axial compressor with averaged rotor tip clearance (1.75% of rotor tip axial chord). An attempt is made to study the compressor stall phenomenon. Computational Fluid Dynamics (CFD) helps in resolving the complex flow features involved in a turbomachinery component and at transonic Mach numbers fairly well. Commercial tool ANSYS CFX is used for solving the 3D compressible Reynolds Averaged Navier-Stokes (RANS) equation with Shear Stress Transport (SST) turbulence model.

Grid independency is carried out for three different mesh size models. All mesh models chosen have fine mesh near wall boundary regions to capture the boundary layer effects. Overall performance maps of the compressor are generated for 50% to 100% rated design speeds in steps of 10% for the chosen optimum grid. Flow variations along the blade annulus are studied for three different operating conditions: choke/free flow, peak efficiency and near stall flow conditions and for different speeds.

Flow parameters such as Mach number, static and total pressure variations, etc. are studied at the inlet to rotor, exit to rotor and exit to stator for the various flow conditions and speeds. The boundary layer growth is clearly captured when the flow is throttled from choke/free flow conditions to near stall condition for all the speeds investigated. Mach number variation along blade height clearly shows decrease in Mach number as stall is approached. Blade loading distribution of the rotor at hub, mean and tip sections are clearly captured. Shock motion from around mid-chord region at free flow condition to towards the leading edge at near stall condition is clearly highlighted. Velocity streamlines near the tip section show the complex interaction of the tip leakage and clearance flows. Velocity vectors near the blade tip shows, the backflow near the trailing edge and tendency for leading edge spillage as the back pressure is increased. The flow blockage region is captured in the meridional plot and the motion of vortex core region as stall is approached is demarcated in the r-θ plots.

Tangential velocity variation across the annulus for the two flow conditions investigated shows stall initiating from the tip section of the blade as compressor is throttled. Flow compensation at near stall conditions is explained.
Selection of Models to Assess the Profile Losses in Blade Rows Using the Methods of Mathematical Statistics
Authors: Baturin Oleg , Kolmakova Daria , Gorshkov Aleksey , Popov Grigorii
Published: February 2016

An investigation of five models used to assess the profile losses in axial turbine cascades appears in this article: Soderberg model, Ainley&Mathieson model, Dunhem&Came model, Kaker&Ocapu model and Central Institute of Aviation Motors (CIAM, Russia) model. Using them, the calculation results were compared with experimental data for 170 airfoil cascades of axial turbines. These cascades include a diversity of blade profiles of axial turbines used in aircraft gas turbine engines. Direct comparison of the calculated and experimental results did not make it possible to uniquely choose the best model. For this reason, the analysis method of loss models based on the statistical analysis of calculation and experimental data deviation was developed. It is shown that the deviations are subject to the normal distribution law. Based on the analysis of mathematical expectations μΔζ and standard deviation σΔζ, it was found that CIAM model gives the results closest to the experimental data. It shows the deviation from the real values of the loss 2±82% with a probability of 95%.
Modeling and Design of Fractional-Order IMC Based Controller for Power Plant Gas Turbine
Authors: Jadhav Sharad P. , Chile Rajan H. , Hamde Satish T.
Published: February 2016

Fractional-order modeling and controller design by a simplified way is the demanding research area and is gearing more and more momentum. This paper is the attempt of application of fractional-order modeling and controller design for the power plant gas turbine. The Gas Turbine is most important equipment in power, aviation and automotive industry. It converts the thermal energy of fuel into the mechanical power. Therefore, important requirement of gas turbine system is to control the flow of input fuel. The existing identified model of the gas turbine between the input fuel flow and the output speed, is of high-order and integer type, which is reduced to the simple and compact integer-order (IO) and fractional-order (FO) models using local optimization technique. The fractional-order internal model controller (FO-IMC) is designed and to show the performance efficacy it is compared with integer-order internal model controller (IO-IMC), which is also designed using the same methodology and specification. Simulation results show that FO-IMC based controller gives better performance for the set point tracking, plant uncertainty and disturbance rejection than the IO-IMC. FO-IMC controller also satisfy the robust stability condition.
Simulations of Non-Reacting Transient N-Dodecane Spray in a High-Pressure Combustion Vessel
Authors: Saini Rohit , De Ashoke
Published: February 2016

In many combustion systems, fuel atomization and the spray breakup process play an important role in determining combustion characteristics and emission formation. Due to the ever-rising need for better fuel efficiency and lower emissions, the development of a fundamental understanding of its process is essential and remains a challenging task. The Spray-A case of the Engine Combustion Network (ECN) is considered in the study, in which liquid n-Dodecane (Spray-A) is injected at 1500 bar through a nozzle diameter of 90 μm into a constant volume vessel with an ambient density of 22.8 kg / m3 and an ambient temperature of 900 K. The unsteady Reynolds averaged Navier-Stokes (URANS) in conjunction with k-ε turbulence model is used to investigate the flow physics in a two-dimensional axisymmetric computational domain. A reduced chemical mechanism from Wang et al. [1] with 100 species and 432 reactions is invoked to represent the kinetics. The gas and liquid phases are modeled using Eulerian-Lagrangian coupled approach. The present model is validated with the experimental data as well as computational data of Pei et al. [2]. Initially, the effects of various turbulence models with modified constants are examined without introducing the breakup phenomena in the computational physics. Later on, primary and secondary breakup processes of the liquid fuel are taken into account. In the present study, we examine the effects of secondary breakup modeling on the spray under high-pressure conditions using different breakup models, including Wave, Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) and Stochastic Secondary Droplet (SSD) models. It has been observed that KH-RT model is more dominant in such high-pressure sprays and predict physics more accurately as compared to other models. The dominance of convection as well as diffusion controlled vaporization model is also realized over the diffusion controlled vaporization model. The investigations at different fuel injection pressures are also modeled and validated with the experimental data [3]. The results strongly suggest that applying high-pressure, leads to high injection velocity and momentum which enhances the air entrainment near the injector region and the mixing process.
Damage Diagnostics of Composite Fan Blades Using the Modified Time Reversal Method
Authors: Jayakody Nimesh , Jha Ratneshwar , Lacy Thomas E.
Published: February 2016

This experimental study presents the Lamb wave based baseline-free diagnostics of damage in a carbon-fiber composite fan blade using the Modified Time Reversal Method (MTRM). A fan blade with delamination was selected as the test specimen and two piezoelectric transducers (PZT) were surface bonded using epoxy adhesive. The system (fan blade and transducers) was then waveform-tuned from which 5.5 cycle tone burst was selected as the optimum excitation waveform. The system was then mode-tuned in order to determine the optimum excitation center frequency. The 55 kHz, 5.5 cycle tone burst was used to generate fundamental asymmetric Lamb waves with high signal-to-noise ratio and low dispersion. Damage Index (DI) values for the fan blade was calculated at equidistant points on a line using both PZTs. Results show that magnitudes of the DI values have strong correlation with the severity of damage present in the fan blade. The procedure followed in this experimental study is directly applicable to the Non Destructive Evaluation (NDE) conducted on composite fan blades. Additionally, this method can be extended to develop a real-time structural health monitoring system for composite fan blades which employs embedded PZTs for actuating and sensing waves.
Multiaxial Fatigue Life Estimation in the Absence of Fatigue Properties: A Case Study on a Turbine Rotor Used in a Typical Turbo Shaft Engine
Authors: Sivaramaiyer Dileep , Shanmugam Esakki Muthu , Udayanan Palani , Degaonkar Girish K.
Published: February 2016

Complex stress strain response of a turbine rotor used in a gas turbine engine was studied. Simple and comprehensive approximation techniques developed by Muralidharan–Manson, Bäumel-Seeger (from data obtained from tension tests) and Roessle–Fatemi (from data obtained from hardness tests) were used to predict the fatigue constants of the rotor material. Multiaxial Fatigue damage models like von Mises equivalent strain model, Smith Watson Topper model, Fatemi–Socie Model, Kandil Brown and Miller model were used to predict the fatigue life of the rotor. Predictions were then compared with the life obtained from the same damage models using the experimental fatigue constants and the life obtained from Low Cycle Fatigue (LCF) testing of the turbine rotor. Acceptable life predictions were obtained with SWT model and FS model using the fatigue constants obtained from the experiment as well as from the approximation techniques. von-Mises equivalent strain model failed to give reasonable life predictions with fatigue constants obtained from the experiment and approximation techniques. The life predicted by KBM model using fatigue constants obtained from approximation techniques (Bäumel-Seeger and Roessle-Fatemi) was found unsatisfactory. The approximation technique proposed by Muralidharan-Manson in combination with all the damage models fitted the failure data within a factor of 5. Finite Element tools were used to determine the stress/strain response of the component under the mutiaxial loading condition.
Probabilistic Fatigue Life Assessment of a Titanium Alloy Impeller for Turbo Shaft Engine Application
Authors: Shanmugam Esakki Muthu , Prakash Raghu V. , Ammaiappan Sakthivel
Published: February 2016

The fatigue life of the titanium alloy centrifugal impeller is estimated based on strain life method. a) Equivalent Strain Method and b) Smith Watson Topper Method are used. The probabilistic analysis of fatigue life is carried out by Weibull distribution method. The fatigue life of the impeller is assessed through cyclic spin test. The results are compared. The Equivalent Strain Method is found non conservative. The average fatigue life of the impeller is estimated as 12000 cycles by SWT method, which is found more closer to test results. The reliability improvement from 95% to 99% reduces the fatigue life around 18%.
A Comparative Study Between Classical and Finite Element Model for Multilayer Viscoelastic Rotors
Authors: Roy H. , Chandraker S.
Published: February 2016

Nowadays, heavy and bulky rotors are replaced by the light yet strong rotor, where the composite material is only supplementary. The composite may be constructed either by reinforcing long unidirectional fiber into matrix material or stacking of lamina, where each lamina has different orientation of fiber. But mathematical modelling of such type of rotor is little difficult when considering different orientation of fiber. This invokes us to construct multilayer rotors of different isotropic material and associated formulation to show its better dynamic performance.

Generally internal damping has an enormous effect on the dynamics of rotor shaft system. For the sake of modelling, all layers are assumed to made of viscoelastic material and perfectly bonded. The constitutive relationship of each layer is represented by two element voigt model and equation of motion is obtained in time domain.

This paper involves the development of both classical and finite element mathematical model of multilayer viscoelastic rotors, which contents system characteristics. Under these conditions, the complex modal behaviour of the rotor-shaft is studied to get an insight of the dynamic characteristics of the system, in terms of Decay rate, Stability Limit of Spin-speed, First Natural Frequency and also Unbalance frequency response.
Thickness and Blade Angle Distribution for Design of Centrifugal Compressor Stage Return Channel Vane
Authors: Bera Arindam , Singh N. K.
Published: February 2016

Return channel de-swirl vanes form an integral part of a centrifugal compressor stage for multi-stage configuration. In this paper, a few configurations of return channel vanes (RCV) are arrived at by modifying the blade angle and thickness distribution from leading edge to the trailing edge. Influence of these two parameters on the overall performance of return channel in terms of total pressure loss co-efficient and static pressure recovery co-efficient along with stage exit flow angle are evaluated through CFD analysis.

CFD results show that, proper thickness distribution after maximum thickness point to the trailing edge improves the stage exit flow angle but not the total pressure loss co-efficient and static pressure recovery co-efficient. Whereas, by suitably modifying the blade angle distribution, all the three performance parameters can be improved considerably.
Experimental Investigation of Overall Cooling Effectiveness on Combustion Chamber Liner With and Without Impingement Holes
Authors: Jesuraj Felix , Rajendran Raghavan , Gottekre Narayanappa Kumar , Yepuri Giridhara Babu , Sasikumar Vivek , Poozhiyil Sinith
Published: February 2016

The gas turbine combustor liner which is subjected to high temperature requires efficient cooling. In earlier days concept of slot film cooling is utilized in the combustion liners and in modern combustors multiple row film cooling (effusion cooling) is mainly used. This study aims at the experimental investigation of overall film cooling effectiveness of an effusion plate with and without impingement holes at the backside. The experiments are done at different blowing ratios and the surface temperature measurements are taken using infrared thermography. The effusion and impingement holes are arranged in staggered manner on two parallel plates and each effusion hole is surrounded by four impingement holes. Effusion holes are drilled at an angle of 27° and the impingement plate is kept at a distance of 6D away from the effusion plate. The experiments are done on the effusion plate with and without impingement plate at the backside. The results show, increase in cooling effectiveness as the blowing ratio increases. The comparative results shows that at a particular blowing ratio the overall cooling effectiveness is higher for effusion plate with impingement holes at the backside due to the higher convective heat transfer coefficients produced by the impinging jets at the cold side of the effusion plate.
Forced Vibration Analysis of Functionally Graded Plates With Geometric Nonlinearity
Authors: Kumar Saurabh , Mitra Anirban , Roy Haraprasad
Published: February 2016

Forced vibration analysis has been carried out on functionally graded plates where the material properties vary along axial direction. The geometric nonlinearity is incorporated in the system using nonlinear strain displacement relations. An indirect methodology is adopted in which the dynamic system is assumed to satisfy the force equilibrium condition at peak excitation amplitude, thus reducing the problem to an equivalent static case. The computational points are selected and start functions are generated at those points by satisfying the flexural and membrane boundary conditions of the plate. The start functions are later used for generating higher order functions using Gram-Schmidt orthogonalisation procedure. The mathematical formulation is based on the variational form of energy principles and the governing equations are derived using Hamilton’s principle. The set of nonlinear governing equations is solved using an iterative direct substitution method employing an appropriate relaxation technique. The results are generated for combinations of clamped and simply supported boundary conditions and presented in amplitude-frequency plane. Three dimensional operational deflection shape plots along with contour plots are also provided for some cases. Results are validated with the works available in the literature.
Effect of Vortex Generators on Film Cooling Effectiveness
Authors: Sarkar S. , Ranakoti Ganesh
Published: February 2016

Film cooling is often adopted, where coolant jets are ejected to form a protective layer on the surface against the hot combustor gases. The bending of jets in crossflow results in Counter Rotating Vortex Pair (CRVP), which is a cause for high jet lift-off and poor film cooling effectiveness in the near field. There are efforts to mitigate this detrimental effect of CRVP and thus to improve the film cooling performance. In the present study, the effects of both downwash and upwash type of vortex generator on film cooling are numerically analysed. A series of discrete holes on a flat plate with 35° streamwise orientation and connected to a common delivery plenum is used here, where the vortex generators are placed upstream of the holes. The blowing ratio and the density ratio are considered as 0.5 and 1.2 respectively with a Reynolds number based on free-stream velocity and diameter of hole being 15885. The computations are performed by ANSYS Fluent 13.0 using k-ε realizable turbulence model. The results show that vortices generated by downwash vortex generator (DWVG) counteracts the effect of CRVP preventing the jet lift-off, which results in increased effectiveness in streamwise as well as in spanwise directions. However, upwash vortex generator (UWVG) augments the effect of CRVP, resulting in poor performance of film cooling.
A Bayesian spatial temporal mixtures approach to kinetic parametric images in dynamic positron emission tomography
Authors: Zhu W. , Ouyang J. , Rakvongthai Y. , Guehl N. J. , Wooten D. W. , El Fakhri G. , Normandin M. D. , Fan Y.
Published: February 2016

Purpose:

Estimation of parametric maps is challenging for kinetic models in dynamic positron emission tomography. Since voxel kinetics tend to be spatially contiguous, the authors consider groups of homogeneous voxels together. The authors propose a novel algorithm to identify the groups and estimate kinetic parameters simultaneously. Uncertainty estimates for kinetic parameters are also obtained.

Methods:

Mixture models were used to fit the time activity curves. In order to borrow information from spatially nearby voxels, the Potts model was adopted. A spatial temporal model was built incorporating both spatial and temporal information in the data. Markov chain Monte Carlo was used to carry out parameter estimation. Evaluation and comparisons with existing methods were carried out on cardiac studies using both simulated data sets and a pig study data. One‐compartment kinetic modeling was used, in which K1 is the parameter of interest, providing a measure of local perfusion.

Results:

Based on simulation experiments, the median standard deviation across all image voxels, of K1 estimates were 0, 0.13, and 0.16 for the proposed spatial mixture models (SMMs), standard curve fitting, and spatial K‐means methods, respectively. The corresponding median mean squared biases for K1 were 0.04, 0.06, and 0.06 for abnormal region of interest (ROI); 0.03, 0.03, and 0.04 for normal ROI; and 0.007, 0.02, and 0.05 for the noise region.

Conclusions:

SMM is a fully Bayesian algorithm which determines the optimal number of homogeneous voxel groups, voxel group membership, parameter estimation, and parameter uncertainty estimation simultaneously. The voxel membership can also be used for classification purposes. By borrowing information from spatially nearby voxels, SMM substantially reduces the variability of parameter estimates. In some ROIs, SMM also reduces mean squared bias.
Effect of reconstruction methods and x‐ray tube current–time product on nodule detection in an anthropomorphic thorax phantom: A crossed‐modality JAFROC observer study
Authors: Thompson J. D. , Chakraborty D. P. , Szczepura K. , Tootell A. K. , Vamvakas I. , Manning D. J. , Hogg P.
Published: February 2016

Purpose:

To evaluate nodule detection in an anthropomorphic chest phantom in computed tomography (CT) images reconstructed with adaptive iterative dose reduction 3D (AIDR3D) and filtered back projection (FBP) over a range of tube current–time product (mAs).

Methods:

Two phantoms were used in this study: (i) an anthropomorphic chest phantom was loaded with spherical simulated nodules of 5, 8, 10, and 12 mm in diameter and +100, −630, and −800 Hounsfield units electron density; this would generate CT images for the observer study; (ii) a whole‐body dosimetry verification phantom was used to ultimately estimate effective dose and risk according to the model of the BEIR VII committee. Both phantoms were scanned over a mAs range (10, 20, 30, and 40), while all other acquisition parameters remained constant. Images were reconstructed with both AIDR3D and FBP. For the observer study, 34 normal cases (no nodules) and 34 abnormal cases (containing 1–3 nodules, mean 1.35 ± 0.54) were chosen. Eleven observers evaluated images from all mAs and reconstruction methods under the free‐response paradigm. A crossed‐modality jackknife alternative free‐response operating characteristic (JAFROC) analysis method was developed for data analysis, averaging data over the two factors influencing nodule detection in this study: mAs and image reconstruction (AIDR3D or FBP). A Bonferroni correction was applied and the threshold for declaring significance was set at 0.025 to maintain the overall probability of Type I error at α = 0.05. Contrast‐to‐noise (CNR) was also measured for all nodules and evaluated by a linear least squares analysis.

Results:

For random‐reader fixed‐case crossed‐modality JAFROC analysis, there was no significant difference in nodule detection between AIDR3D and FBP when data were averaged over mAs [F(1, 10) = 0.08, p = 0.789]. However, when data were averaged over reconstruction methods, a significant difference was seen between multiple pairs of mAs settings [F(3, 30) = 15.96, p < 0.001]. Measurements of effective dose and effective risk showed the expected linear dependence on mAs. Nodule CNR was statistically higher for simulated nodules on images reconstructed with AIDR3D (p < 0.001).

Conclusions:

No significant difference in nodule detection performance was demonstrated between images reconstructed with FBP and AIDR3D. mAs was found to influence nodule detection, though further work is required for dose optimization.
Putting a chain on mutant
KRAS
Authors: Behjati Sam
Published: February 2016

A promising inhibitor of the oncogene
KRAS
, which locks KRAS in its inactive state, has been developed.
Mycobacterium and Aerobic Actinomycete Culture: Are Two Medium Types and Extended Incubation Times Necessary?
Authors: Simner Patricia J. , Doerr Kelly A. , Steinmetz Lory K. , Wengenack Nancy L.
Published: February 2016

Mycobacterial cultures are historically performed using a liquid medium and a solid agar medium with an incubation period of up to 60 days. We performed a retrospective analysis of 21,494 mycobacterial and aerobic actinomycetes cultures performed over 10 months to determine whether two medium types remain necessary and to investigate whether culture incubation length can be shortened. Specimens were cultured using Bactec MGIT liquid medium and Middlebrook 7H11/S7H11 solid medium with incubation periods of 42 and 60 days, respectively. Time-to-positivity and the identity of isolates recovered from each medium were evaluated. A total of 1,205/21,494 cultures (6%) were positive on at least one medium. Of the 1,353 isolates recovered, 1,110 (82%) were nontuberculous mycobacteria, 145 (11%) were aerobic actinomycetes, and 98 (7%) were
Mycobacterium tuberculosis
complex. Assessing medium types, 1,121 isolates were recovered from solid medium cultures, 922 isolates were recovered from liquid medium cultures, and 690 isolates were recovered on both media. Liquid cultures were positive an average of 10 days before solid cultures when the two medium types were positive (
P
< 0.0001). Isolates detected on solid medium after 6 weeks of incubation included 65 (5%) nontuberculous mycobacteria, 4 (0.3%) aerobic actinomycetes, and 2 (0.2%) isolates from the
M. tuberculosis
complex. Medical chart review suggested that most of these later-growing isolates were insignificant, as the diagnosis was already known, or they were considered colonizers/contaminants. This study reaffirms the need for both liquid medium and solid medium for mycobacterial and aerobic actinomycetes culture and demonstrates that solid medium incubation times may be reduced to 6 weeks without significantly impacting sensitivity.
Development of a Highly Specific IgM Enzyme-Linked Immunosorbent Assay for Bartonella henselae Using Refined
N
-Lauroyl-Sarcosine-Insoluble Proteins for Serodiagnosis of Cat Scratch Disease
Authors: Otsuyama Ken-ichiro , Tsuneoka Hidehiro , Kondou Kaori , Yanagihara Masashi , Tokuda Nobuko , Shirasawa Bungo , Ichihara Kiyoshi
Published: February 2016

The conventional anti-
Bartonella henselae
IgM enzyme-linked immunosorbent assay (IgM-ELISA) methods for diagnosing cat scratch disease (CSD) remain poor in both sensitivity and specificity. We sought to develop an IgM-ELISA with improved accuracy in the serodiagnosis of CSD by exploring the antigens that are most suitable for an ELISA. We prepared 5 different protein antigens: antigen I (sonicated
B. henselae
whole-cell antigen), antigen II (
N
-lauroyl-sarcosine-insoluble antigen), antigen III (processed sarcosine-soluble antigen), and antigen IV and antigen V (sarcosine-insoluble and sarcosine-soluble antigens refined by DEAE-Sepharose Fast Flow ion-exchange chromatography). The IgM antibodies in the sera of 47 patients with clinically suspected CSD (24 definite, 23 suspected) and of 85 healthy individuals were examined by ELISAs using the 5 antigens, and the results were compared with those of an IgM indirect fluorescent antibody assay (IgM-IFA). In a reference panel, which consisted of 5 positive and 5 negative sera, antigen I and antigen III failed to distinguish between the two statuses, whereas the other three antigens succeeded in distinguishing between them. When the cutoff value was set at the 98th percentile of the ELISA index for healthy individuals, the sensitivity of IgM-IFA for the 24 cases of definite CSD was 54%, whereas the sensitivities of the IgM-ELISAs with antigen II, IV, and V were 75%, 83%, and 75%, respectively. The sensitivities of these three IgM-ELISAs for all 47 of the clinically suspected cases were 49%, 64%, and 51%, respectively. In contrast, the sensitivity of IgM-IFA was 28%. These results indicate that the refined sarcosine-insoluble proteins (antigen IV), which possessed the highest specificity among the 5 antigens, are the most appropriate for developing an IgM-ELISA for the highly specific serodiagnosis of CSD.
Comparative Evaluation of the Novel bioNexia Legionella Test with the BinaxNOW Legionella Card Assay and the Sofia Legionella FIA Assay for Detection of Legionella pneumophila (Serogroup 1) Antigen in Urine Samples
Authors: Congestrì Francesco , Crepaldi Elisabetta , Gagliardi Marina , Pedna Maria Federica , Sambri Vittorio
Published: February 2016

A new immunochromatographic test (bioNexia
Legionella
; bioMérieux) for the detection of
Legionella pneumophila
urinary antigen was evaluated in 255 urine samples. The results were compared with those obtained by the BinaxNOW and Sofia
Legionella
tests. The novel test compared well with those currently in use.
Evaluation of GenoFlow DR-MTB Array Test for Detection of Rifampin and Isoniazid Resistance in Mycobacterium tuberculosis
Authors: Molina-Moya B. , Kazdaglis G. , Lacoma A. , Prat C. , Gómez A. , Villar-Hernández R. , García-García E. , Haba L. , Maldonado J. , Samper S. , Ruiz-Manzano J. , Ausina V. , Domínguez J.
Published: February 2016

The aim of this study was to evaluate the GenoFlow DR-MTB array test (DiagCor Bioscience, Hong Kong) on 70 cultured isolates and 50 sputum specimens. The GenoFlow array test showed good sensitivity and specificity compared to the phenotypic Bactec 460TB. This array accurately detected mutations in
rpoB
,
katG
, and
inhA
associated with resistance to rifampin and isoniazid.
Sequence Diversity, Intersubgroup Relationships, and Origins of the Mouse Leukemia Gammaretroviruses of Laboratory and Wild Mice
Authors: Bamunusinghe Devinka , Naghashfar Zohreh , Buckler-White Alicia , Plishka Ronald , Baliji Surendranath , Liu Qingping , Kassner Joshua , Oler Andrew J. , Hartley Janet , Kozak Christine A.
Published: February 2016

Mouse leukemia viruses (MLVs) are found in the common inbred strains of laboratory mice and in the house mouse subspecies of
Mus musculus
. Receptor usage and envelope (
env
) sequence variation define three MLV host range subgroups in laboratory mice: ecotropic, polytropic, and xenotropic MLVs (E-, P-, and X-MLVs, respectively). These exogenous MLVs derive from endogenous retroviruses (ERVs) that were acquired by the wild mouse progenitors of laboratory mice about 1 million years ago. We analyzed the genomes of seven MLVs isolated from Eurasian and American wild mice and three previously sequenced MLVs to describe their relationships and identify their possible ERV progenitors. The phylogenetic tree based on the receptor-determining regions of
env
produced expected host range clusters, but these clusters are not maintained in trees generated from other virus regions. Colinear alignments of the viral genomes identified segmental homologies to ERVs of different host range subgroups. Six MLVs show close relationships to a small xenotropic ERV subgroup largely confined to the inbred mouse Y chromosome.
env
variations define three E-MLV subtypes, one of which carries duplications of various sizes, sequences, and locations in the proline-rich region of
env
. Outside the
env
region, all E-MLVs are related to different nonecotropic MLVs. These results document the diversity in gammaretroviruses isolated from globally distributed
Mus
subspecies, provide insight into their origins and relationships, and indicate that recombination has had an important role in the evolution of these mutagenic and pathogenic agents.

IMPORTANCE
Laboratory mice carry mouse leukemia viruses (MLVs) of three host range groups which were acquired from their wild mouse progenitors. We sequenced the complete genomes of seven infectious MLVs isolated from geographically separated Eurasian and American wild mice and compared them with endogenous germ line retroviruses (ERVs) acquired early in house mouse evolution. We did this because the laboratory mouse viruses derive directly from specific ERVs or arise by recombination between different ERVs. The six distinctively different wild mouse viruses appear to be recombinants, often involving different host range subgroups, and most are related to a distinctive, largely Y-chromosome-linked MLV ERV subtype. MLVs with ecotropic host ranges show the greatest variability with extensive inter- and intrasubtype envelope differences and with homologies to other host range subgroups outside the envelope. The sequence diversity among these wild mouse isolates helps define their relationships and origins and emphasizes the importance of recombination in their evolution.
An 86-year-old man with acute abdominal pain
Authors: van Dam Paul M E L , Posthouwer Dirk
Published: February 2016

An 86-year-old man presented with severe pain in the upper abdomen along with fever. On physical examination, we found an arterial blood pressure of 84/43 mm Hg, a heart rate of 80 bpm and a temperature of 38.3°C. The abdomen was painful and peristalsis was absent. Empiric antibiotic therapy for sepsis was started with amoxicillin/clavulanate and gentamicin. CT scan of the abdomen revealed an emphysematous cholecystitis. Percutaneous ultrasound-guided cholecystostomy was applied. Bile cultures revealedClostridium perfringens. Emphysematous cholecystitis is a life-threatening form of acute cholecystitis that occurs as a consequence of ischaemic injury to the gallbladder, followed by translocation of gas-forming bacteria (ie,C. perfringens,Escherichia coli, Klebsiellaand Streptococci). The mortality associated with emphysematous cholecystitis is higher than in non-emphysematous cholecystitis (15% vs 4%). Therefore, early diagnosis with radiological imaging is of vital importance.
Predicting admission at triage: are nurses better than a simple objective score?
Authors: Cameron Allan , Ireland Alastair J , McKay Gerard A , Stark Adam , Lowe David J
Published: February 2016

Aim

We compared two methods of predicting hospital admission from ED triage: probabilities estimated by triage nurses and probabilities calculated by the Glasgow Admission Prediction Score (GAPS).

Methods

In this single-centre prospective study, triage nurses estimated the probability of admission using a 100 mm visual analogue scale (VAS), and GAPS was generated automatically from triage data. We compared calibration using rank sum tests, discrimination using area under receiver operating characteristic curves (AUC) and accuracy with McNemar's test.

Results

Of 1829 attendances, 745 (40.7%) were admitted, not significantly different from GAPS’ prediction of 750 (41.0%, p=0.678). In contrast, the nurses’ mean VAS predicted 865 admissions (47.3%), overestimating by 6.6% (p<0.0001). GAPS discriminated between admission and discharge as well as nurses, its AUC 0.876 compared with 0.875 for VAS (p=0.93). As a binary predictor, its accuracy was 80.6%, again comparable with VAS (79.0%), p=0.18. In the minority of attendances, when nurses felt at least 95% certain of the outcome, VAS’ accuracy was excellent, at 92.4%. However, in the remaining majority, GAPS significantly outperformed VAS on calibration (+1.2% vs +9.2%, p<0.0001), discrimination (AUC 0.810 vs 0.759, p=0.001) and accuracy (75.1% vs 68.9%, p=0.0009). When we used GAPS, but ‘over-ruled’ it when clinical certainty was ≥95%, this significantly outperformed either method, with AUC 0.891 (0.877–0.907) and accuracy 82.5% (80.7%–84.2%).

Conclusions

GAPS, a simple clinical score, is a better predictor of admission than triage nurses, unless the nurse is sure about the outcome, in which case their clinical judgement should be respected.