bluuebunny/crossref_metadata_2025 huggingface dataset:
Transfer of the DDG-51 Ship Service Gas Turbine Generator (SSGTG) Marine Electrical Power System Assembly and Installation to the Republic of Korea Navy KDX-III Destroyer Program
Authors: Shaw Jesse , Kim Sungon
Published: September 2014

In 2004, Rolls-Royce Naval Marine, Inc. (RRNMI, Walpole, MA, USA, now Rolls-Royce Marine North America, RRMNA) reached an agreement with Samsung Techwin Co. Ltd. (Seoul and Changwon, Korea) for the transfer of the assembly and installation of a marine electrical power system. This agreement culminated in the installation and use of Rolls-Royce Ship Service Gas Turbine Generators (SSGTGs) in the Republic of Korea Navy (RoKN) KDX-III Destroyers. In order to deliver success for this program, both companies had to overcome numerous technical and non-technical challenges.

Among these challenges were:

- Development of a kitting structure supplemented with tailored assembly drawings and instructions that could duplicate an established production process

- Agreement on the amount of Korean labor and materials to be utilized, referred to as “in-country” content

- Development of appropriate and necessary training for the assembly and testing of AG9140RF SSGTGs

- Determination of a correlation factor which equalizes the variables between RRMNA’s engine test cell and Samsung Techwin’s engine test cell

- Application of DAPA Quality Assurance (QA) requirements upon a system designed in accordance with US Navy QA requirements

- Ensuring compliance with Export Control guidelines, Export License requirements, and Manufacturing License Agreements

- Obtaining US Government approval for sale and transfer of technology and hardware to the Republic of Korea (RoK)
Microscopic Analysis of Fatigue Damage Accumulation in TiAl Intermetallics
Authors: Patriarca Luca , Içöz Can , Filippini Mauro , Beretta Stefano
Published: September 2014

In order to design efficient and light components for the aircraft industry preserving the safety of the design, more sophisticated design criteria are required for the application of new materials. In particular, the usage of novel manufacturing processes to produce advanced materials such as the gamma titanium aluminide alloys (γ-TiAl) requires the investigation of the microstructure influence in the fatigue damage accumulation processes. In this work we examine a Ti-48Al-2Cr-2Nb alloy obtained with an additive manufacturing technique by Electron Beam Melting (EBM) by conducting monotonic and fatigue experiments both on tension and compression samples. The full-field residual strain maps corresponding to different applied stress levels and number of cycles are obtained through the use of high-resolution Digital Image Correlation (DIC). The strain maps were overlaid with the images of the microstructure and detailed analyses were performed to investigate the features of the microstructure where high local strain heterogeneities arise. High local residual plastic shear strains were measured inside lamellar colonies, which are detected as the precursor to fatigue crack initiation. The measure of the residual strains also provides further information on the role of the intermetallic phases on the fatigue behavior of γ-TiAl alloys.
An Experimental Study of Influence of the Steam Injection on the Profile Surface on the Turbine Nozzle Cascade Performance
Authors: Gribin Vladimir , Tishchenko Aleksandr , Tishchenko Victor , Gavrilov Ilya , Khomiakov Sergey , Popov Vitalij , Lisyanskiy Alexander , Nekrasov Alexander , Nazarov Vladimir , Usachev Konstantin
Published: September 2014

The paper presents the results of experiments on the effect of steam injection on the performance of the wet steam turbine nozzle cascade. The steam injection destroys a liquid film on the surface of the blade and reduces erosion and dangerous droplets after cascade. The results obtained in the vane package cascade which include a slot on the concave surface of the airfoil near the trailing edge of blades. Experimental studies were carried out on wet and superheated steam. A pneumatic measurement system was used to determine the parameters of the main and injection steam. A laser diagnostics system “POLIS” that includes PIV/PTV was used to analyze the impact of heating steam injection on the characteristics of the liquid phase. Profile losses were obtained at different steam parameters and steam injection speeds. The characteristics of the liquid phase behind the trailing edge were obtained in a wide range of operating parameters.
A Soot Chemistry Model That Captures Fuel Effects
Authors: Puduppakkam Karthik V. , Modak Abhijit U. , Naik Chitralkumar V. , Camacho Joaquin , Wang Hai , Meeks Ellen
Published: September 2014

A detailed chemistry model is necessary to simulate the effects of variations in fuel composition on soot emissions. In this work, we have developed a detailed chemistry model for the soot formation and oxidation chemistry, with a focus on the surface kinetics of the soot-particle. The model has been compared to a unique set of soot particle-size data measured in flames for several single-component fuels. Fuel components used in the experiments represent the chemical classes found in jet, gasoline, and diesel fuels, including n-heptane (representative of n-alkanes) and toluene (aromatic). Measurements were taken in burner-stabilized stagnation-flame (BSSF) experiments, which can be simulated well using the 1-dimensional BSSF flame model in CHEMKIN-PRO. Soot volume fraction and particle size distributions are modeled using the sectional method option for Particle Tracking, within CHEMKIN-PRO software. The well-characterized flow of the BSSF experiments allows the modeling to focus on the kinetics. Validated detailed reaction mechanisms for fuel combustion and PAH production, combined with the new soot surface-kinetics mechanism, were used in the simulations. Simulation results were compared to measurements for both particle size distributions and total soot volume fraction. Observed effects of fuel, temperature, pressure, equivalence ratio and residence time on the soot size distribution shape and soot quantity were reproduced by the model.

The chemistry in the soot surface model includes particle nucleation, growth through the HACA (hydrogen-abstraction/carbon-addition) and PAH-condensation (polycyclic aromatic hydrocarbons) pathways, as well as soot-oxidation pathways. In addition to soot chemistry, the physics of particle coagulation and aggregation were included in the model. The results demonstrate the ability of well-validated chemistry to predict both dramatic and subtle effects related to soot mass and soot particle size.
Reduction in Greenhouse Gas Emissions in the Power Industry Using Compressed Air Power Enhancement Technology in Gas Turbines
Authors: Arias Quintero S. , Auerbach S. , Randel J. , Kraft R.
Published: September 2014

Environmental and supply considerations are playing a pivotal key in the economics and operation rationale behind power generation. A once fossil-fuel dependent industry is embracing renewable sources, albeit slowed by technical and economic challenges. With gas turbines comprising a large part of the world’s electric generation pool, increasing the power output of the existing combined cycle plants and avoiding the use of less efficient peakers has the potential of reducing greenhouse gas emissions. Performance simulations show that compressed air injection can increase the power output of 2×1 combined cycle “F” class plants above 40 MW, equivalent to the typical output of simple cycle peaking units. Resultant total power output can be maintained while reducing pollutants, infrastructure resources, and capital cost compared to peaking plants.
Ceramic Matrix Composites for High Pressure Turbine Vanes
Authors: Boyle Robert J. , Parikh Ankur H. , Nagpal Vinod K. , Halbig Michael C. , DiCarlo James A.
Published: September 2014

Through thickness, hoop, and spanwise component stresses were calculated for two Ceramic Matrix Composite (CMC) vane configurations. The analyses are for the first stage vane of a High Pressure Turbine. One configuration is for a vane with trailing edge ejection, and the other has no trailing edge ejection. The effects of analyzing separate pressure and thermal loads, as well as combining these loads, are examined. For the case without trailing edge ejection the effects of variations in the stiffness modulus are given. Results are discussed for the midspan region as well as for the entire span. Pressure loads were determined assuming a mainstream gas and coolant pressure of 50 atm. Thermal loads were determined assuming a gas temperature of 2141°K(3394°F), and a maximum Environmental Barrier Coating temperature of 1756°K(2700°F). The desired maximum CMC temperature was 1589°C(2400°F).
Development and Validation of a Modal Analysis Code for Wind Turbine Blades
Authors: Lennie Matthew , Marten David , Pechlivanoglou Georgios , Nayeri Christian Navid , Paschereit Christian Oliver
Published: September 2014

QBlade is an open source wind turbine design and simulation tool developed at the Berlin Institute of Technology. To enable a coupling with the aeroelastic simulation tool FAST from NREL an aditional module, called QFEM, was created and integrated with QBlade. This module performs a modal analysis on rotor blades designed in QBlade using isotropic tapered Euler Beam elements. The newly developed module now provides structural properties to the National Renewable Energy Laboratorys aeroelasticity simulation tool FAST. The 2D structural properties of the beam elements are created using integration methods. A number of test cases show that the 2D integration methods and beam element code work with adaquete accuracy. The integration of the modal analysis code greatly facilitates the structural design and analysis of rotor blades and will be made available to the public under an open source license.
Flow in a Rotating Cavity With Axial Throughflow at Engine Representative Conditions
Authors: Atkins Nicholas R. , Kanjirakkad Vasudevan
Published: September 2014

The prediction of compressor drum cavity heat transfer is an important factor in the overall design of an aero engine. The rotationally dominated flow field within the cavity governs the heat transfer conditions by suppressing the motion of the fluid. Without heating, the fluid in the outer region of the cavity can approach solid body rotation. The outer cavity fluid is disturbed by the bore flow at the inner radius. The resultant bore flow vortex has been shown to exhibit many different modes of behaviour, dependent on the Rossby number. At higher Rossby number the bore flow vortex has been shown to break down into a precessing radial arm. It has also been shown that the hot drive arm (shroud) between the compressor stages destabilises the flow field through natural convection. This paper presents data from the Sussex Multiple Cavity Rig, which matches the fluid dynamic conditions of a compressor bore in terms of axial throughflow, rotational Reynolds number and Grashof number. It features titanium alloy discs, which are instrumented with surface thermocouples. This paper presents data which helps to separate the effects of throughflow Reynolds number, rotational Reynolds number and Grashof number on the dimensionless disc temperature profiles. In order to illustrate the flow structures this paper presents a hybrid RANS/LES model for the two highest Reynolds number cases. For these cases, the numerical simulations show a change from stable to unstable stratification with an increase in the bore to shroud temperature ratio in good qualitative agreement with the measured data.
Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry: Part II — Detailed Flow Analysis
Authors: Ubben Stefan , Niehuis Reinhard
Published: September 2014

The combination of variable speed control and adjustable diffuser vanes offers an attractive design option for centrifugal compressors applied in industrial applications where a wide operating range at high efficiency level and a favorable surge line is required. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall which is mandatory since the diffuser geometry adjustment has to take place during operation, is still not satisfying.

The results of characteristic line and probe measurements presented in Part I [18] of this two-part paper showed that an one-sided diffuser clearance not necessarily need to lead to a negative impact on compressor operating behavior but is able to contribute to an increase in flow range, stall margin, pressure ratio and efficiency, as long as the diffuser passage is broad enough with respect to the clearance height.

In order to reveal the relevant flow phenomena, in Part II the results of detailed measurements of the pressure distribution at diffuser exit and Particle Image Velocimetry (PIV) measurements inside the diffuser channel performed at three clearance configurations and three diffuser angles at a fixed radial gap are discussed. It was found, that for defined diffuser configurations the clearance flow amplifies the diffuser throat vortex capable to reduce the loading of the highly loaded vane pressure side and to support a more homogenous diffuser flow. It turned out that the coaction of the geometry parameter diffuser vane angle and diffuser clearance height is of particular importance.

The experimental results are published as an open CFD testcase “Radiver 2” [17], extending the experimental data base of the testcase “Radiver” published in 2003 by Ziegler [24].
Experimental and Numerical Investigation of Corner Stall in a Highly-Loaded Compressor Cascade
Authors: Zhang Yanfeng , Mahallati Ali , Benner Michael
Published: September 2014

Three-dimensional corner stall is one of the most important factors limiting compressor performance. This paper presents a complementary experimental and computational study of corner stall in a highly-loaded compressor cascade subjected to three inlet boundary layer thicknesses, two levels of freestream turbulence intensity and two Reynolds numbers. Experiments included seven-hole pressure probe traverses, airfoil loading and surface oil flow visualization. Measurements were supplemented with the numerical predictions from a commercially available CFD code. It was found that the low momentum boundary layer on the endwall was unable to overcome the large streamwise adverse pressure gradient in this high-lift profile and turned sharply towards the midspan due to the strong cross-passage pressure gradient. The corner stall, with distinct regions of three-dimensional reversed flow, started at 50% chord and occupied a large area of the suction surface as well as the downstream passage. Only a small region of the inlet boundary layer, very close to the endwall seemed to play a role in the corner stall. As such, the flow in the endwall region was found to be nearly independent of the inlet boundary layer thickness, freestream turbulence intensity and Reynolds number. Based on the endwall flow structures, a new topology of corner stall for compressor cascades with high airfoil diffusion factor and high flow turning has also been proposed.
POD-Driven Adaptive Sampling for Efficient Surrogate Modeling and its Application to Supersonic Turbine Optimization
Authors: Kato Hiromasa , Funazaki Ken-ichi
Published: September 2014

A new approach for adaptively sampling a design parameter space using an error estimate through the reconstruction of flow field by a combination of proper orthogonal decomposition (POD) and radial basis function network (RBFN) is presented. It differs from other similar approaches in that it does not use the reconstructed flow field by POD for the evaluation of objective functions, and thus it can be a subset of the flow field. Advantages of this approach include the ease of constructing a chain of simulation codes as well as the flexibility of choosing where and what to reconstruct within the solution domain. An improvement in achieving a good prediction quality, with respect to other adaptive sampling methods, has been demonstrated using supersonic impulse turbine optimization as the test case. A posteriori validation of the surrogate models were also carried out using a set of separately-evaluated samples, which showed a similar trend as the Leave-One-Out (LOO) cross-validation. The progressively enriched surrogate model was then used to achieve the more uniformly populated Pareto front with fewer number of function evaluations.
High Pressure Subsonic Nucleation in 1D Nozzles — An Experimental Study
Authors: Guo Tao , Burnett Mark , Turnquist Norman , Moraga Francisco
Published: September 2014

The presence of moisture in steam turbines is known to cause blade erosion and reduce turbine performance. As a result, nucleating wet steam flow has been the topic of both academic and engineering research for many decades. However, almost all of the previous experimental studies on steam nucleation have been carried out under low pressure supersonic flow conditions, either in converging-diverging (Laval) nozzles or in supersonic airfoil cascades. Some recent experimental studies conducted droplet size/wetness measurements within actual turbines, but these tests in general only give qualitative assessment on the nucleation phenomena. They are not intended to study the mechanisms of the nucleating steam flow.

In this paper, an experimental study of nucleating wet steam flow under high-pressure subsonic flow conditions is presented. In particular, the world’s first high-pressure subsonic nucleation test rig was designed and built at the GE Global Research Center. This advanced test rig takes high pressure (up to 1000 psia) clean steam with controlled inlet superheat and expands it through 1D subsonic nozzles. The Wilson line location and the length of the nucleation zone are controlled through different combinations of inlet steam pressure and superheat, and overall pressure ratios.

An advanced optical measurement system was developed and used to measure the Wilson line, the ensuing condensation zone, and the droplet size and number density generated from nucleation. The flow path in the nozzle is visible through specially designed sapphire windows. The optical system is essentially comprised of two laser-photodiode pairs (405 nm and 689 nm wavelength), which can be traversed along the length of the nozzle.

The experiment data have indicated that significant differences exist between high pressure subsonic nucleation and low pressure supersonic nucleation. Further, an in-house 1D analytical tool as well as a 3D multiphase CFD have been used to model the test runs, and reasonable agreements have been obtained. This study has direct application in the design of Nuclear and Concentrated Solar high pressure steam turbines.
Using Tiptiming and Strain Gauge Data for the Estimation of Consumed Life in a Compressor Blisk Subjected to Stall-Induced Loading
Authors: Kharyton Vsevolod , Bladh Ronnie
Published: September 2014

Using tip timing technology to record blade vibratory behavior has grown to become an industry standard over the past decade. Typically, the technology gets used during engine prototype testing to verify safe operation of the blades and thus the engine through synchronous and non-synchronous excitation events. Another common application is blade health monitoring, where the technique is used to detect deviations in natural frequencies and/or amplitudes compared to the virgin state. In both cases, acquired response data are used to establish that blade stresses remain below the high cycle fatigue limit. More rarely is tip timing data used as basis for remaining life estimation.

As an example of how tip timing technology can be used beyond traditional resonance clearance for new blade designs, this paper presents an assessment of the fatigue damage incurred to a transonic compressor rotor subjected to stall-induced dynamic loading. The compressor rotor in question is equipped with tip timing, as well as strain gauges for a limited set of airfoils. The dynamic loads at stall are non-synchronous and highly erratic in nature, leading to quasi-static response of multiple modes. To facilitate a conceptually straightforward time domain finite life fatigue analysis, different strategies are employed to reconstruct the stress-time signal from tip timing data. This in turn allows for quantification of accumulated damage cycles, which is here done through simplified and traditional rainflow counting techniques.

Additionally, a non-standard way of processing of tip timing data was employed to overcome one of tip timing method drawbacks — frequency aliasing. As an approach the nonuniform Fourier transform was applied to the same data sets. The results obtained are thoroughly evaluated and compared with strain gauges results highlighting the benefits and limitations of the respective approaches for highly complex stress-time histories such as stall events.
Switch Triggers for Optimal Vibration Reduction via Resonance Frequency Detuning
Authors: Lopp Garrett K. , Kauffman Jeffrey L.
Published: September 2014

For systems subjected to linear frequency sweep excitation, piezoelectric-based resonance frequency detuning provides vibration reduction by altering the stiffness state of the material as it passes through resonance. This vibration reduction technique applies to turbomachinery experiencing changes in rotation speed, for example on spool-up and spool-down. The peak response dynamics are determined by the system’s sweep rate, modal damping ratio, electromechanical coupling coefficient, and, most importantly, the frequency at which the stiffness state is altered. An analytical approach is employed to solve the nondimensional single degree of freedom equation of motion and is scaled to incorporate the altered system frequency following the stiffness state switch. This paper provides an extensive study over a range of sweep rates, damping ratios, and electromechanical coupling coefficients to determine the optimal frequency switch trigger that minimizes the response envelope. This switch trigger is primarily a function of the electromechanical coupling coefficient and the phase of vibration at which the switch occurs. As the coupling coefficient increases, the switch trigger decreases and is approximately linear with the square of this coupling coefficient. Furthermore, as with other state-switching techniques, the optimal frequency switch occurs when the phase of vibration is at the point of maximum displacement, or peak strain energy.
Volute CFD Modeling Evaluation for Centrifugal Compressors
Authors: Samale Anil , Pacheco Jorge E.
Published: September 2014

Significant effort has been spent over the years to improve the accuracy and reduce the Computational Fluid Dynamics (CFD) simulation time required to predict performance for centrifugal compressors. Most of the emphasis has been on modeling the impeller and diffuser components. This paper presents an evaluation of volute modeling targeted at reducing simulation time while increasing the accuracy of the results. Providing accurate predictions of performance and operating range is critical to the equipment users as it allows reduction in design margins for plant equipment dependent on compressor performance (i.e. drivers, intercoolers and other auxiliary equipment).

The volute is the component that collects the flow from the diffuser and guides it into the discharge nozzle. Due to the circumferential variation (tongue) in the geometry, this component has to be modeled in its entirety (360 degrees); which results in very large grid sizes. The impeller and diffuser, normally modeled as a sector or pie slice, result in significantly smaller meshes. The volute models require large numbers of computing nodes to be solved and tend to have convergence issues.

The investigation, with the objective of reducing the amount of time required to run these simulations and improve the convergence of the runs, evaluated several mesh configurations that focused on grid density (element count), element aspect ratio and use of inflation layers. The domain evaluated consisted of several stationary components and one rotating component. The model started at the inlet guide vane section followed by the impeller, vanned diffuser, volute, and discharge nozzle. Commercial software ANSYS CFX was used to develop the meshes using tetrahedral/prism elements and complete steady-state CFD analyses.

Detailed flow field characteristics (total and static pressure, velocity streamlines, etc.) and key performance parameters (loss coefficient, pressure ratio, etc.) were compared for the various configurations evaluated. In addition, experimental measurements were used to validate the CFD results. The configuration that resulted in the shortest cycle time with the best performance accuracy was selected as optimum. Accuracy is paramount for performance prediction and reduction in simulation time will allow more volute iterations to be investigated, which would help improve volute performance in centrifugal compressors.
Effect of Cavities on Impeller Aeromechanical Forcing in a Low Pressure Ratio Centrifugal Compressor Stage
Authors: Clancy Cathal , Moyroud François , Ramakrishnan Kishore
Published: September 2014

Previous experimental and CFD investigation on a GE Oil & Gas centrifugal compressor stage with a vaneless diffuser revealed a complex excitation mechanism caused by aero-acoustic interaction between three blade rows. Recent published studies have indicated that cavities enclosing shrouded impellers may strongly amplify the acoustic excitation of the impeller by Tyler-Sofrin modes. In this current research therefore, the previous CFD study is expanded to include a model of the disk and shroud cavities. A linearized Navier-Stokes frequency sweep in forced response mode shows a well-defined peak in cavity acoustic activity at a certain frequency. It also shows that the inclusion of cavities noticeably increases the modal forcing on the impeller, qualitatively confirming findings in existing literature. A significant difference in modal force magnitude is found between the shroud-disk out-of-phase mode and the in-phase mode, which is consistent with experimental measurements of vibratory response.
Analysis of Stochastic Bifurcation and Chaos in a Rub-Impact Rotor System With Random Parameter
Authors: Yang Yongfeng , Gao Zhe , Zhang Meng , Wang Gang
Published: September 2014

Stochastic bifurcation and chaos of a rub-impact rotor system with random parameter is studied in this paper. Due to an irrational and fractional expression existing in the rub-impact force, there is a very complicated integral operation. Then, the Taylor series expansion is proposed, and it expands the rub-impact force into a polynomial. Firstly, take SD oscillator for example, the results show the taylor series expansion method is acceptable. Secondly, expand the rub-impact force, the numerical results indicate that the method is available to the rub-impact rotor system. At last, the Chebyshev polynomial approximation method is applied to reduce the system with random parameter to its equivalent deterministic one, and the responses of stochastic system can be obtained by numerical methods. Numerical simulations show that random parameters have a significant effect on the rub-impact rotor system.
On the Effect of Altitude on the Performance of a Small Wind Turbine Blade
Authors: Pourrajabian Abolfazl , Mirzaei Masoud , Ebrahimi Reza , Wood David
Published: September 2014

This study deals with the effect of the altitude on the performance of a Small Wind Turbine (SWT) blade. Four potential regions of wind energy with altitudes up to 3,000 m were selected and a three-bladed, 2 m diameter small HAWT was designed for those regions. Starting time was combined with output power in an objective function to improve the performance of the turbine at low wind speeds. The goals of the objective function, the output power and the starting performance, were addressed by geometry optimization of the blade which was carried out by the genetic algorithm. The modified Blade-Element Momentum (BEM) theory was applied to calculate the output power and starting time. Results show that the performance of an optimal blade which was optimized for operating at sea level degrades for other regions. That degradation is more important for the starting performance in comparison with the reduction of the power coefficient. To improve the performance of the blade in the considered regions, two redesign procedures were carried out. First, the geometry of the blade was optimized respect to the air density of the regions which led to increase of the power coefficient and the starting time. Much more power was achieved using the second approach in which the tip speed ratio was added to the geometry of the blade as an additional design variable. Results also indicate that the generator resistive torque remarkably puts off the starting of the turbine especially at very high altitudes.
Cascaded systems analysis of photon counting detectors
Authors: Xu J. , Zbijewski W. , Gang G. , Stayman J. W. , Taguchi K. , Lundqvist M. , Fredenberg E. , Carrino J. A. , Siewerdsen J. H.
Published: September 2014

Purpose:

Photon counting detectors (PCDs) are an emerging technology with applications in spectral and low‐dose radiographic and tomographic imaging. This paper develops an analytical model of PCD imaging performance, including the system gain, modulation transfer function (MTF), noise‐power spectrum (NPS), and detective quantum efficiency (DQE).

Methods:

A cascaded systems analysis model describing the propagation of quanta through the imaging chain was developed. The model was validated in comparison to the physical performance of a silicon‐strip PCD implemented on an experimental imaging bench. The signal response, MTF, and NPS were measured and compared to theory as a function of exposure conditions (70 kVp, 1–7 mA), detector threshold, and readout mode (i.e., the option for coincidence detection). The model sheds new light on the dependence of spatial resolution, charge sharing, and additive noise effects on threshold selection and was used to investigate the factors governing PCD performance, including the fundamental advantages and limitations of PCDs in comparison to energy‐integrating detectors (EIDs) in the linear regime for which pulse pileup can be ignored.

Results:

The detector exhibited highly linear mean signal response across the system operating range and agreed well with theoretical prediction, as did the system MTF and NPS. The DQE analyzed as a function of kilovolt (peak), exposure, detector threshold, and readout mode revealed important considerations for system optimization. The model also demonstrated the important implications of false counts from both additive electronic noise and charge sharing and highlighted the system design and operational parameters that most affect detector performance in the presence of such factors: for example, increasing the detector threshold from 0 to 100 (arbitrary units of pulse height threshold roughly equivalent to 0.5 and 6 keV energy threshold, respectively), increased the f50 (spatial‐frequency at which the MTF falls to a value of 0.50) by ∼30% with corresponding improvement in DQE. The range in exposure and additive noise for which PCDs yield intrinsically higher DQE was quantified, showing performance advantages under conditions of very low‐dose, high additive noise, and high fidelity rejection of coincident photons.

Conclusions:

The model for PCD signal and noise performance agreed with measurements of detector signal, MTF, and NPS and provided a useful basis for understanding complex dependencies in PCD imaging performance and the potential advantages (and disadvantages) in comparison to EIDs as well as an important guide to task‐based optimization in developing new PCD imaging systems.
H3K27me and PRC2 transmit a memory of repression across generations and during development
Authors: Gaydos Laura J. , Wang Wenchao , Strome Susan
Published: September 2014

Establishing memory of gene repression

Although cells in the body contain the same DNA content, they can display widely varying form and function among tissues. This comes about by differential gene regulation and by establishing a type of gene expression memory that is passed down during cell division to daughter cells. Gaydos
et al.
report that in nematodes, both sperm and oocytes transmit a memory of chromatin repression to embryos in the form of modified histones. During DNA replication, modified histones are passed to daughter chromatids to provide chromatin memory for a few cell divisions. Histone-modifying enzymes replenish histone modifications and provide long-term chromatin memory.

Science
, this issue p.
1515
Observation of Fermi surface deformation in a dipolar quantum gas
Authors: Aikawa K. , Baier S. , Frisch A. , Mark M. , Ravensbergen C. , Ferlaino F.
Published: September 2014

Aligning a magnetic atomic gas

When a bunch of fermions get together, they obey the Pauli exclusion principle: No two fermions can be in the same quantum state. The fermions populate the available states, starting from those lowest in energy. The boundary between the empty and filled states is called the Fermi surface (FS). For cold gases of fermionic atoms in the lab, the FS is usually spherical. Now, Aikawa
et al.
observe the FS squishing in a gas of Er atoms, which behave like tiny magnets and align with their magnetic field environment. The squishing reflects the very directional interactions between the Er atoms.

Science
, this issue p.
1484
Synthesis and detection of a seaborgium carbonyl complex
Authors: Even J. , Yakushev A. , Düllmann Ch. E. , Haba H. , Asai M. , Sato T. K. , Brand H. , Di Nitto A. , Eichler R. , Fan F. L. , Hartmann W. , Huang M. , Jäger E. , Kaji D. , Kanaya J. , Kaneya Y. , Khuyagbaatar J. , Kindler B. , Kratz J. V. , Krier J. , Kudou Y. , Kurz N. , Lommel B. , Miyashita S. , Morimoto K. , Morita K. , Murakami M. , Nagame Y. , Nitsche H. , Ooe K. , Qin Z. , Schädel M. , Steiner J. , Sumita T. , Takeyama M. , Tanaka K. , Toyoshima A. , Tsukada K. , Türler A. , Usoltsev I. , Wakabayashi Y. , Wang Y. , Wiehl N. , Yamaki S.
Published: September 2014

A carbonyl compound that tips the scales

Life is short for the heaviest elements. They emerge from high-energy nuclear collisions with scant time for detection before they break up into lighter atoms. Even
et al.
report that even a few seconds is long enough for carbon to bond to the 106th element, seaborgium (see the Perspective by Loveland). The authors used a custom apparatus to direct the freshly made atoms out of the hot collision environment and through a stream of carbon monoxide and helium. They compared the detected products with theoretical modeling results and conclude that hexacarbonyl Sg(CO)
6
was the most likely structural formula.

Science
, this issue p.
1491
; see also p.
1451
Biomimetics and evolution
Authors: Patek S. N.
Published: September 2014

Linking biomechanical and evolutionary analysis helps to create viable biomimetic products
Superheavy carbonyls
Authors: Loveland Walter
Published: September 2014

The radioactive superheavy element seaborgium can form a carbonyl compound during its short lifetime

[Also see Report by

Even
et al.

]
The Pope tackles sustainability
Authors: McNutt Marcia
Published: September 2014

The war on environmental degradation has a powerful new ally: Pope Francis. Prompted by a Joint Workshop of the Pontifical Academy of Sciences and the Pontifical Academy of Social Sciences on sustainability that was convened in May 2014, the Vatican has articulated some of its strongest environmental statements to date, calling for all of us to take personal responsibility and redirect our relationship with nature to ensure the future habitability and sustainability of this planet (see the Perspective on p. 1457). The problems that motivate the Vatican are no different from those that concern the scientific community: depletion of nonrenewable resources, loss of ecosystem services, and risks from changing climate. But what the Vatican contributes is the rationale for taking action: because it is our moral responsibility to bequeath a habitable planet to future generations.
Ebola vaccine: Little and late
Authors: Cohen Jon
Published: September 2014

Scaling up production of Ebola vaccines and treatments will take many months.
No miracles
Authors: Morell Virginia
Published: September 2014

Biologist Russell Gray uses evolutionary ideas to probe the origin of languages and complex thinking.
16S rRNA Gene Sequencing, Multilocus Sequence Analysis, and Mass Spectrometry Identification of the Proposed New Species “Clostridium neonatale”
Authors: Bouvet Philippe , Ferraris Laurent , Dauphin Brunhilde , Popoff Michel-Robert , Butel Marie Jose , Aires Julio
Published: September 2014

In 2002, an outbreak of necrotizing enterocolitis in a Canadian neonatal intensive care unit was associated with a proposed novel species of
Clostridium
, “
Clostridium neonatale
.” To date, there are no data about the isolation, identification, or clinical significance of this species. Additionally,
C. neonatale
has not been formally classified as a new species, rendering its identification challenging. Indeed, the
C. neonatale
16S rRNA gene sequence shows high similarity to another
Clostridium
species involved in neonatal necrotizing enterocolitis,
Clostridium butyricum
. By performing a polyphasic study combining phylogenetic analysis (16S rRNA gene sequencing and multilocus sequence analysis) and phenotypic characterization with mass spectrometry, we demonstrated that
C. neonatale
is a new species within the
Clostridium
genus
sensu stricto
, for which we propose the name
Clostridium neonatale
sp. nov. Now that the status of
C. neonatale
has been clarified, matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) can be used for better differential identification of
C. neonatale
and
C. butyricum
clinical isolates. This is necessary to precisely define the role and clinical significance of
C. neonatale
, a species that may have been misidentified and underrepresented during previous neonatal necrotizing enterocolitis studies.
First Report of Westerdykella dispersa as a Cause of an Angioinvasive Fungal Infection in a Neutropenic Host
Authors: Sue Paul K. , Gurda Grzegorz T. , Lee Richard , Watkins Tonya , Green Rachel , Memon Warda , Milstone Aaron M. , Zelazny Adrian M. , Fahle Gary A. , Pham Thu Anh , Gibas Connie F. , Sutton Deanna A. , Wickes Brian L. , Wiederhold Nathan P. , Zhang Sean X.
Published: September 2014

Angioinvasive fungal infections (AFIs) are an important cause of morbidity and mortality among immunocompromised patients. However, clinicomicrobiological characteristics and treatment of many AFI agents remain poorly defined. We report the first human case of infection with
Westerdykella dispersa
, an emergent cause of AFI, which was successfully treated in a neutropenic pediatric patient.
A Single-Tube Multiple-Locus Variable-Number Tandem-Repeat Analysis of Mycoplasma pneumoniae Clinical Specimens by Use of Multiplex PCR-Capillary Electrophoresis
Authors: Yan Chao , Sun Hongmei , Xue Guanhua , Zhao Hanqing , Wang Liqiong , Feng Yanling , Li Shaoli
Published: September 2014

In this study, we developed a single-tube multiple-locus variable-number tandem-repeat (VNTR) analysis (MLVA) assay to type
Mycoplasma pneumoniae
directly from respiratory samples collected from children with respiratory infections. The multiplex PCR included four fluorescently primed VNTRs (Mpn13, Mpn14, Mpn15, and Mpn16) and was carried out in a single tube. A total of 137
M. pneumoniae
-positive specimens, collected in 2013 from Beijing, China, were divided among four types (M4-5-7-2, M4-5-6-2, M3-5-6-2, and M5-5-7-2) using the amended MLVA system. The most prevalent genotype was M4-5-7-2. No correlation was found between macrolide resistance in the
M. pneumoniae
samples and the MLVA types. To our knowledge, this is the first study to type and analyze
M. pneumoniae
clinical specimens using multiplex PCR-capillary electrophoresis in a single tube. This novel low-cost method can be used to rapidly type
M. pneumoniae
clinical specimens directly and shows great potential for monitoring outbreaks of
M. pneumoniae
.
Evaluation of the BD Max MRSA
XT
Assay for Use with Different Swab Types
Authors: Dalpke Alexander H. , Hofko Marjeta , Stock Christian , Zimmermann Stefan
Published: September 2014

We evaluated the performance of the BD Max MRSA
XT
assay for use with different swab types. The 90% detection rates (95% confidence intervals) were 387 (97 to 1,551), 877 (238 to 3,230), 986 (183 to 5,287), 1,292 (328 to 5,078), 2,400 (426 to 13,518), and 5,848 (622 to 55,021) CFU/swab for Liquid Stuart, Liquid Amies, dry, Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs (Becton Dickinson), respectively. Amies Gel without charcoal, ESwab collection, and Amies gel with charcoal swabs had a tendency to be less sensitive, but none of the differences was statistically significant.
Molecular Requirement for Sterols in Herpes Simplex Virus Entry and Infectivity
Authors: Wudiri George A. , Pritchard Suzanne M. , Li Hong , Liu Jin , Aguilar Hector C. , Gilk Stacey D. , Nicola Anthony V.
Published: September 2014

Herpes simplex virus 1 (HSV-1) required cholesterol or desmosterol for virion-induced membrane fusion. HSV successfully entered DHCR24
−/−
cells, which lack a desmosterol-to-cholesterol conversion enzyme, indicating that entry can occur independently of cholesterol. Depletion of desmosterol from these cells resulted in diminished HSV-1 entry, suggesting a general sterol requirement for HSV-1 entry and that desmosterol can operate in virus entry. Cholesterol functioned more effectively than desmosterol, suggesting that the hydrocarbon tail of cholesterol influences viral entry.
Development of Dose-Response Models of Creutzfeldt-Jakob Disease Infection in Nonhuman Primates for Assessing the Risk of Transfusion-Transmitted Variant Creutzfeldt-Jakob Disease
Authors: Huang Yin , Gregori Luisa , Anderson Steven A. , Asher David M. , Yang Hong
Published: September 2014

Estimates for the risk of transmitting variant Creutzfeldt-Jakob disease (vCJD) via blood transfusion have relied largely on data from rodent experiments, but the relationship between dose (amount of infected blood) and response (vCJD infection) has never been well quantified. The goal of this study was to develop a dose-response model based on nonhuman primate data to better estimate the likelihood of transfusion-transmitted vCJD (TTvCJD) in humans. Our model used dose-response data from nonhuman primates inoculated intracerebrally (i.c.) with brain tissues of patients with sporadic and familial CJD. We analyzed the data statistically by using a beta-Poisson dose-response model. We further adjusted model parameters to account for the differences in infectivity between blood and brain tissue and in transmission efficiency between intravenous (i.v.) and i.c. routes to estimate dose-dependent TTvCJD infection. The model estimates a mean infection rate of 76% among recipients who receive one unit of whole blood collected from an infected donor near the end of the incubation period. The nonhuman primate model provides estimates that are more consistent with those derived from a risk analysis of transfused nonleukoreduced red blood cells in the United Kingdom than prior estimates based on rodent models.

IMPORTANCE
TTvCJD was recently identified as one of three emerging infectious diseases posing the greatest immediate threat to the safety of the blood supply. Cases of TTvCJD were reported in recipients of nonleukoreduced red blood cells and coagulation factor VIII manufactured from blood of United Kingdom donors. As the quantity of abnormal prions (the causative agent of TTvCJD) varies significantly in different blood components and products, it is necessary to quantify the dose-response relationship for a wide range of doses for the vCJD agent in transfused blood and plasma derivatives. In this paper, we suggest the first mechanistic dose-response model for TTvCJD infection based on data from experiments with nonhuman primates. This new model may improve estimates of the possible risk to humans.
Characterization of an Alphamesonivirus 3C-Like Protease Defines a Special Group of Nidovirus Main Proteases
Authors: Blanck Sandra , Stinn Anne , Tsiklauri Lali , Zirkel Florian , Junglen Sandra , Ziebuhr John
Published: September 2014

Cavally virus (CavV) and related viruses in the family
Mesoniviridae
diverged profoundly from other nidovirus lineages but largely retained the characteristic set of replicative enzymes conserved in the
Coronaviridae
and
Roniviridae
. The expression of these enzymes in virus-infected cells requires the extensive proteolytic processing of two large replicase polyproteins, pp1a and pp1ab, by the viral 3C-like protease (3CL
pro
). Here, we show that CavV 3CL
pro
autoproteolytic cleavage occurs at two N-terminal (N1 and N2) and one C-terminal (C1) processing site(s). The mature form of 3CL
pro
was revealed to be a 314-residue protein produced by cleavage at FKNK
1386
|SAAS (N2) and YYNQ
1700
|SATI (C1). Site-directed mutagenesis data suggest that the mesonivirus 3CL
pro
employs a catalytic Cys-His dyad comprised of CavV pp1a/pp1ab residues Cys-1539 and His-1434. The study further suggests that mesonivirus 3CL
pro
substrate specificities differ from those of related nidovirus proteases. The presence of Gln (or Glu) at the P1 position was not required for cleavage, although residues that control Gln/Glu specificity in related viral proteases are retained in the CavV 3CL
pro
sequence. Asn at the P2 position was identified as a key determinant for mesonivirus 3CL
pro
substrate specificity. Other positions, including P4 and P1′, each are occupied by structurally related amino acids, indicating a supportive role in substrate binding. Together, the data identify a new subgroup of nidovirus main proteases and support previous conclusions on phylogenetic relationships between the main nidovirus lineages.

IMPORTANCE
Mesoniviruses have been suggested to provide an evolutionary link between nidovirus lineages with small (13 to 16 kb) and large (26 to 32 kb) RNA genome sizes, and it has been proposed that a specific set of enzymes, including a proofreading exoribonuclease and other replicase gene-encoded proteins, play a key role in the major genome expansion leading to the currently known lineages of large nidoviruses. Despite their smaller genome size (20 kb), mesoniviruses retained most of the replicative domains conserved in large nidoviruses; thus, they are considered interesting models for studying possible key events in the evolution of RNA genomes of exceptional size and complexity. Our study provides the first characterization of a mesonivirus replicase gene-encoded nonstructural protein. The data confirm and extend previous phylogenetic studies of mesoniviruses and related viruses and pave the way for studies into the formation of the mesonivirus replication complex and functional and structural studies of its functional subunits.