bluuebunny/crossref_metadata_2025 huggingface dataset:
Development and Demonstration of a Stability Management System for Gas Turbine Engines
Authors: Christensen D. , Cantin P. , Gutz D. , Szucs P. N. , Wadia A. R. , Armor J. , Dhingra M. , Neumeier Y. , Prasad J. V. R.
Published: May 2008

Rig and engine test processes and in-flight operation and safety for modern gas turbine engines can be greatly improved with the development of accurate on-line measurement to gauge the aerodynamic stability level for fans and compressors. This paper describes the development and application of a robust real-time algorithm for gauging fan/compressor aerodynamic stability level using over-the-rotor dynamic pressure sensors. This real-time scheme computes a correlation measure through signal multiplication and integration. The algorithm uses the existing speed signal from the engine control for cycle synchronization. The algorithm is simple and is implemented on a portable computer to facilitate rapid real-time implementation on different experimental platforms as demonstrated both on a full-scale high-speed compressor rig and on an advanced aircraft engine. In the multistage advanced compressor rig test, the compressor was moved toward stall at constant speed by closing a discharge valve. The stability management system was able to detect an impending stall and trigger opening of the valve so as to avoid compressor surge. In the full-scale engine test, the engine was configured with a one-per-revolution distortion screen and transients were run with a significant amount of fuel enrichment to facilitate stall. Test data from a series of continuous rapid transients run in the engine test showed that in all cases, the stability management system was able to detect an impending stall and manipulated the enrichment part of the fuel schedule to provide stall-free transients.
Rapid Prototyping Design Optimization Using Flow Sculpting
Authors: Dawes W. N.
Published: May 2008

Computational fluid dynamics has become a mature art form and its use in turbomachinery design has become commonplace. Simple blade-blade simulations run at near interactive rates but anything involving complex geometry—such as turbine cooling—turns around too slowly to participate in realistic design cycles; this is mostly due to the difficulty of modifying and meshing the geometry. Simulations for complex geometries are run afterwards as a check—rather than at the critical conceptual design phase. There is a clear opportunity for some sort of rapid prototyping but fully 3D simulation to remedy this. This paper reports work exploring the relationship between solid modeling, mesh generating, and flow solving in the general context of design optimization but with the emphasis on rapid prototyping. In particular, the work is interested in the opportunities derived by tightly integrating these traditionally separate activities together within one piece of software. The near term aim is to ask the question: how might a truly virtual, rapid prototyping design system, with a tactile response such as sculpting in clay, be constructed? This paper reports the building blocks supporting that ambition.
Aerodynamic Design, Model Test, and CFD Analysis for a Multistage Axial Helium Compressor
Authors: Yan X. , Takizuka T. , Kunitomi K. , Itaka H. , Takahashi K.
Published: May 2008

Results of an aerodynamic design study for the multistage axial helium compressor of a 300 MWe class nuclear gas turbine are presented. Helium compressor aerodynamics is challenged by the characteristically narrow and numerous-stage flow path, which enhances loss effects of blade surface and end wall boundary layer growth, secondary and clearance flows, and any occurrence of flow separation and stage mismatch. To meet the high efficiency and reliability requirements of the nuclear application, base line and advanced aerodynamic design techniques are incorporated with the intent to mitigate the flow path adverse working condition and losses. Design validation is carried out by test and test-calibrated 3D viscous CFD analyses of a subscale model compressor. In addition to verifying the success of the design intent, the data and computational insights of overall performance and internal flow behavior are used to establish a performance model based on Reynolds number and used for the full compressor performance prediction. The model applicable to all geometrically similar designs shows sensitive responses of helium compressor aerodynamic efficiency to Reynolds number and surface roughness. Presented in the paper is the first modern design with experimental validation for multistage axial helium compressor that concerned itself with a difficult past but which has strong current interest in countries now developing thermal and fast nuclear gas reactors.
A Novel Antivortex Turbine Film-Cooling Hole Concept
Authors: Heidmann James D. , Ekkad Srinath
Published: May 2008

A novel turbine film-cooling hole shape has been conceived and designed at NASA Glenn Research Center. This “antivortex” design is unique in that it requires only easily machinable round holes, unlike shaped film-cooling holes and other advanced concepts. The hole design is intended to counteract the detrimental vorticity associated with standard circular cross-section film-cooling holes. This vorticity typically entrains hot freestream gas and is associated with jet separation from the turbine blade surface. The antivortex film-cooling hole concept has been modeled computationally for a single row of 30 deg angled holes on a flat surface using the 3D Navier–Stokes solver GLENN-HT. A blowing ratio of 1.0 and density ratios of 1.05 and 2.0 are studied. Both film effectiveness and heat transfer coefficient values are computed and compared to standard round hole cases for the same blowing rates. A net heat flux reduction is also determined using both the film effectiveness and heat transfer coefficient values to ascertain the overall effectiveness of the concept. An improvement in film effectiveness of about 0.2 and in net heat flux reduction of about 0.2 is demonstrated for the antivortex concept compared to the standard round hole for both blowing ratios. Detailed flow visualization shows that as expected, the design counteracts the detrimental vorticity of the round hole flow, allowing it to remain attached to the surface.
Heat/Mass Transfer Characteristics in Angled Ribbed Channels With Various Bleed Ratios and Rotation Numbers
Authors: Kim Kyung Min , Park Suk Hwan , Jeon Yun Heung , Lee Dong Hyun , Cho Hyung Hee
Published: May 2008

The present study investigates the effects of secondary flow due to angled rib turbulators on the heat/mass transfer in the square channels with channel rotation and bleed flow. The angle of attack of the angled ribs was 45deg. The bleed holes were located between the rib turbulators on either the leading or trailing surface. The tests were conducted under the conditions corresponding to various bleed ratios (BR=0.0, 0.2, and 0.4) and rotation numbers (Ro=0.0, 0.2, and 0.4) at Re=10,000. The results suggest that the heat/mass transfer characteristics were influenced by the Coriolis force, the decrement of the main flow rate, and the secondary flow. In the 90deg angled ribbed channel, the heat/mass transfer reduced on the leading surface with an increment in the rotation number, but it increased on the trailing surface. However, it decreased on both surfaces in the 45deg angled ribbed channel. As the bleed ratio increased, the Sherwood number ratios decreased on both the bleeding and nonbleeding surfaces for the 45deg angled ribs but increased on the bleeding surface for the 90deg angled ribs.
An Experimental and Computational Heat Transfer Study of Pulsating Jets
Authors: Utturkar Yogen , Arik Mehmet , Seeley Charles E. , Gursoy Mustafa
Published: May 2008

Synthetic jets are meso or microscale fluidic devices, which operate on the “zero-net-mass-flux” principle. However, they impart a positive net momentum flux to the external environment and are able to produce the cooling effect of a fan sans its ducting, reliability issues, and oversized dimensions. The rate of heat removal from the thermal source is expected to depend on the location, orientation, strength, and shape of the jet. In the current study, we investigate the impact of jet location and orientation on the cooling performance via time-dependent numerical simulations and verify the same with experimental results. We firstly present the experimental study along with the findings. Secondly, we present the numerical models/results, which are compared with the experiments to gain the confidence in the computational methodology. Finally, a sensitivity evaluation has been performed by altering the position and alignment of the jet with respect to the heated surface. Two prime orientations of the jet have been considered, namely, perpendicular and cross jet impingement on the heater. It is found that if jet is placed at an optimum location in either impingement or cross flow position, it can provide similar enhancements.
Investigation of Turbulent Flow and Heat Transfer in Periodic Wavy Channel of Internally Finned Tube With Blocked Core Tube
Authors: Wang Qiu-Wang , Lin Mei , Zeng Min , Tian Lin
Published: May 2008

Three-dimensional complex turbulent flow and heat transfer of internally longitudinally finned tube with blocked core tube and streamwise wavy fin are numerically investigated. The numerical method is validated by comparing the calculated results with corresponding experimental data. The effects of both wave height and wave distance on heat transfer performance are examined. The range of wave height to hydraulic diameter ratio is from 0.61 to 2.45, and that of wave distance to hydraulic diameter ratio is from 3.06 to 14.69, while that of Reynolds number is from 904 to 4520. The computational results demonstrate that the Nusselt number and friction factor increase with the increase of the wave height, while they decrease with the increase of the wave distance. Furthermore, general correlations are proposed to describe the performance of the wavy configuration for 904⩽Re⩽4520, 0.61⩽s∕de⩽2.45, 6.12⩽l∕de⩽11.02, with the mean deviations for heat transfer and friction factor correlations being −2.8% and −1.9%, respectively.
Simultaneous Retrieval of Total Hemispherical Emissivity and Specific Heat From Transient Multimode Heat Transfer Experiments
Authors: Venugopal G. , Deiveegan M. , Balaji C. , Venkateshan S. P.
Published: May 2008

Transient cooling experiments of a heated vertical aluminum plate with an embedded heater, in quiescent air, were conducted for the simultaneous estimation of total hemispherical emissivity and specific heat of the plate material. During cooling, the heat loss from the hot plate by natural convection and radiation was taken into account. During the experiments, plate temperatures were recorded at several locations using a data acquisition system. A numerically computed transient response of the plate is then compared with the experimentally known transient response to estimate the residual, the minimization of which using Levenberg–Marquardt’s iterative procedure retrieves the parameters pertinent to the problem. The experiments were conducted for three different surface emissivities of the plate obtained by using suitable surface treatment. A consistency test for the present approach was also done by conducting transient heating experiments using the retrieved values of parameters and a comparison of simulated and calculated natural convection heat transfer coefficients as a function of temperature. The experiments have been performed over a temperature range of 320–430K and a Rayleigh number range of 2×106–2×107. The emissivity values are in good agreement with previous reported results.
Influence of Interfacial Mixing on Thermal Boundary Conductance Across a Chromium/Silicon Interface
Authors: Hopkins Patrick E. , Norris Pamela M. , Stevens Robert J. , Beechem Thomas E. , Graham Samuel
Published: May 2008

The thermal conductance at solid-solid interfaces is becoming increasingly important in thermal considerations dealing with devices on nanometer length scales. Specifically, interdiffusion or mixing around the interface, which is generally ignored, must be taken into account when the characteristic lengths of the devices are on the order of the thickness of this mixing region. To study the effect of this interfacial mixing on thermal conductance, a series of Cr films is grown on Si substrates subject to various deposition conditions to control the growth around the Cr∕Si boundary. The Cr∕Si interfaces are characterized with Auger electron spectroscopy. The thermal boundary conductance (hBD) is measured with the transient thermoreflectance technique. Values of hBD are found to vary with both the thickness of the mixing region and the rate of compositional change in the mixing region. The effects of the varying mixing regions in each sample on hBD are discussed, and the results are compared to the diffuse mismatch model (DMM) and the virtual crystal DMM (VCDMM), which takes into account the effects of a two-phase region of finite thickness around the interface on hBD. An excellent agreement is shown between the measured hBD and that predicted by the VCDMM for a change in thickness of the two-phase region around the interface.
Bipolar Plate Thermal Response to PEM Fuel Cell Stack Compressive Load
Authors: Fekrazad N. , Bergman T. L.
Published: May 2008

This technical brief reports new findings regarding the strong relationship between the temperature of the bipolar plates of a proton exchange membrane fuel cell stack and thermal conditions within the membranes of the stack. The unique feature of the study is the notion that bipolar plate temperature might be used as an indicator to identify optimal stack clamping pressures that lead to nearly isothermal conditions inside the stack. Uniform thermal (and humidity) conditions are expected to enhance fuel cell durability and reliability.
Hysteresis Curve in Reproduction of Reynolds’ Color-Band Experiments
Authors: Kanda Hidesada , Yanagiya Takayuki
Published: May 2008

This article describes the reproduction and extended analysis of Reynolds’ color-band experiment. Reynolds found two critical Reynolds numbers (Rc) in pipe flows: Rc1 of 12,830 from laminar to turbulent flow and Rc2 of 2030 from turbulent to laminar flow. Since no clear relationship has been established between them, we studied how the entrance shape affects Rc. Thus, for the first time, a hysteresis graph can be drawn by connecting the two curves of Rc1 and Rc2 such that the two Rc values lie on separate branches of the hysteresis plot.
A Separation Criterion With Experimental Validation for Shear-Driven Films in Separated Flows
Authors: Friedrich M. A. , Lan H. , Wegener J. L. , Drallmeier J. A. , Armaly B. F.
Published: May 2008

The behavior of a shear-driven thin liquid film at a sharp expanding corner is of interest in many engineering applications. However, details of the interaction between inertial, surface tension, and gravitational forces at the corner that result in partial or complete separation of the film from the surface are not clear. A criterion is proposed to predict the onset of shear-driven film separation from the surface at an expanding corner. The criterion is validated with experimental measurements of the percent of film mass separated as well as comparisons to other observations from the literature. The results show that the proposed force ratio correlates well to the onset of film separation over a wide range of experimental test conditions. The correlation suggests that the gas phase impacts the separation process only through its effect on the liquid film momentum.
A Series Pressure Drop Representation for Flow Through Orifice Tubes
Authors: Jankowski T. A. , Schmierer E. N. , Prenger F. C. , Ashworth S. P.
Published: May 2008

A simple model is developed here to predict the pressure drop and discharge coefficient for incompressible flow through orifices with length-to-diameter ratio greater than zero (orifice tubes) over wide ranges of Reynolds number. The pressure drop for flow through orifice tubes is represented as two pressure drops in series; namely, a pressure drop for flow through a sharp-edged orifice in series with a pressure drop for developing flow in a straight length of tube. Both of these pressure drop terms are represented in the model using generally accepted correlations and experimental data for developing flows and sharp-edged orifice flow. We show agreement between this simple model and our numerical analysis of laminar orifice flow with length-to-diameter ratio up to 15 and for Reynolds number up to 150. Agreement is also shown between the series pressure drop representation and experimental data over wider ranges of Reynolds number. Not only is the present work useful as a design correlation for equipment relying on flow through orifice tubes but it helps to explain some of the difficulties that previous authors have encountered when comparing experimental observation and available theories.
Comparison of Interfacial Forces During Post-Chemical-Mechanical-Polishing Cleaning
Authors: Ng Dedy , Liang Hong
Published: May 2008

This research investigates the interfacial forces involved in tribological interactions while removing nanosized particles during post-chemical-mechanical polishing cleaning. Surface and interfacial forces are discussed to understand the particle adhesion and subsequent removal through physical and chemical interactions. Approaches include theoretical analysis combined with experimental study. The theoretical analysis was focused on the forces that exist between particles and a substrate. Surface interaction consideration includes applied pressure, frictional force, and hydrodynamic drag. The polishing experiments were carried out on silicon wafers with SiO2 slurry. Cleaning experiments were performed in de-ionized water using a polyvinyl acetal brush to remove particles from a hydrophilic-silicon surface. The fluid-drag force was found to affect the lubricating behavior of cleaning through changing material properties. Values of interfacial forces and their effects on cleaning were discussed along with a lubricating model system.
Investigation of Contact Stiffness and Contact Damping for Magnetic Storage Head-Disk Interfaces
Authors: Shi Xi , Polycarpou Andreas A.
Published: May 2008

As the areal density of magnetic disk storage continues to increase and head-disk spacing decreases, contact between the recording slider and the rotating media becomes imminent. In order to predict contact forces, fly-height modulations, and off-track motions, dynamic models are typically used. A critical element of these models is the contact stiffness and damping arising from the interfacial interaction between the slider and the disk. In this paper, we review different models for predicting contact stiffness based on roughness and layered media and then we report experimental data of both contact stiffness and contact damping of typical head-disk interfaces. It is found that the contact stiffness models (based on roughness alone) overpredict the contact stiffness of actual head-disk interfaces by as much as an order of magnitude. Also, it is found that the contact damping ratio is typically few percent and its behavior is substrate dependent. In addition, the effects of a molecularly thin lubricant and humidity on contact stiffness and damping were experimentally investigated and no significant effects were found.
Interaction of Asperities on Opposing Surfaces in Thin Film, Mixed Elastohydrodynamic Lubrication
Authors: Choo Jian W. , Olver Andrew V. , Spikes Hugh A. , Dumont Marie-Laure , Ioannides Eustathios
Published: May 2008

A novel experimental method has been developed to investigate how model asperities, on opposing surfaces in an elastohydrodynamic (EHD) contact, interact to influence the lubricant film distribution. This technique allows direct measurements of lubricant film thickness during asperity-asperity collision. A surface having a single transverse ridge asperity was rubbed against a second surface having three different roughness features, a transverse ridge, multiple transverse ridges, and an array of hemispherical bumps to study the resultant micro-EHD films. This work reveals how the film thickness is greatly reduced when the peaks of opposing asperities coincide, and how asperities can combine to cause a larger volume of lubricant to be entrapped at their leading edges. The new technique described shows considerable promise for the study of mixed lubrication.
High-Speed Rotor With Air Bearings Mounted on Flexible Supports: Test Bench and Experimental Results
Authors: Belforte G. , Colombo F. , Raparelli T. , Viktorov V.
Published: May 2008

A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1kg mass and 37mm diameter is rotated up to 75,000rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown.
An Experimental Study of Oil-Lubricated Journal Bearings Undergoing Oscillatory Motion
Authors: Lu Xiaobin , Khonsari M. M.
Published: May 2008

A distinctive behavior of an oil-lubricated journal bearing undergoing oscillatory motion is the evolution of friction hysteresis as it traverses from boundary, to mixed, and to hydrodynamic regime. In this paper, the results of a series of experiments are reported to examine the effects of load, with or without oil, oil type, oil inlet temperature, and oscillating frequency on the friction hysteresis. Three types of hysteresis loop were found. The inertia of the lubricant flow contributes to the friction hysteresis.
Three-Dimensional Rough Surface Contact Model for Anisotropic Materials
Authors: He Ling , Ovaert Timothy C.
Published: May 2008

By applying the line integral of Barnett–Lothe tensors on oblique planes, the three-dimensional rough surface contact problem for a semi-infinite anisotropic elastic half-plane in contact with a rough rigid sphere is formulated. The conjugate gradient technique of analytical continuation was employed to determine the contact parameters. The general solutions due to varying degrees of anisotropy and mechanical boundary conditions are obtained, and examples with fiber-reinforced composites are presented.
Observations of Acoustic Emission Under Conditions of Varying Specific Film Thickness for Meshing Spur and Helical Gears
Authors: Raja Hamzah R. I. , Al-Balushi Khamis R. , Mba D.
Published: May 2008

This paper presents experimental findings on the generation of acoustic emission (AE) from operational spur and helical gears as a function of specific film thickness (λ). The latter was varied while the gears were operating by spraying liquid nitrogen onto the rotating gear wheel over a range of load and speed conditions. It was observed that the level of AE activity was dependent on the specific film thickness (λ) and consequently the level asperity contact. The presented finding on both spur and helical gears is the first known attempt at correlating friction, film thickness, and gear operating conditions with AE.
Transition in Wall-Bounded Flows
Authors: Lee C. B. , Wu J. Z.
Published: May 2008

In this paper, we present direct comparisons of experimental results on transition in wall-bounded flows obtained by flow visualizations, hot-film measurement, and particle-image velocimetry, along with a brief mention of relevant theoretical progresses, based on a critical review of about 120 selected publications. Despite somewhat different initial disturbance conditions used in experiments, the flow structures were found to be practically the same. The following observed flow structures are considered to be of fundamental importance in understanding transitional wall-bounded flows: the three-dimensional nonlinear wave packets called solitonlike coherent structures (SCSs) in boundary layer and pipe flows, the Λ-vortex, the secondary vortex loops, and the chain of ring vortices. The dynamic processes of the formation of these structures and transition as newly discovered by recent experiments include the following: (1) The sequential interaction processes between the Λ-vortex and the secondary vortex loops, which control the manner by which the chain of ring vortices is periodically introduced from the wall region into the outer region of the boundary layer. (2) The generation of high-frequency vortices, which is one of the key issues for understanding both transitional and developed turbulent boundary layers (as well as other flows), of which several explanations have been proposed but a particularly clear interpretation can be provided by the experimental discovery of secondary vortex loops. The ignorance of secondary vortex loops would make the dynamic processes and flow structures in a transitional boundary layer inconsistent with previous discoveries. (3) The dominant role of SCSs in all turbulent bursting, which is considered as the key mechanism of turbulent production in a low Reynolds-number turbulent boundary layer. Of direct relevance to bursting is the low-speed streaks, whose formation mechanism and link to the flow structures in wall-bounded flows can be answered more clearly than before in terms of the SCS dynamics. The observed SCSs and secondary vortex loops not only enable revisiting the classic story of wall-bounded flow transition, but also open a new avenue to reconstruct the possible universal scenario for wall-bounded flow transition.
Numerical Simulation for Vortex Structure in a Turbopump Inducer: Close Relationship With Appearance of Cavitation Instabilities
Authors: Kimura Toshiya , Yoshida Yoshiki , Hashimoto Tomoyuki , Shimagaki Mitsuru
Published: May 2008

Unsteady cavitation phenomena such as rotating cavitation and cavitation surge are often observed in a turbopump inducer of a rocket engine, sometimes causing undesirable oscillation of the system. Investigation of their mechanism and prediction of such unsteady phenomena are, therefore, crucial in the design of inducers. As many experiments have shown, the appearance of cavitation instability is highly related to the flow rate as well as to the inlet casing geometry. Experimental observations have shown that a very complex flow structure, including such phenomena as backflow and vortices, appears upstream of the inducer. In this work, therefore, we conducted 3D unsteady computational fluid dynamics simulations of noncavitating flow in a turbopump inducer, mainly focusing on the vortex structure, for three types of inlet casing geometry with various flow rates. Simulation results showed that the vortex structure for the geometry of the inlet casing and that for the flow rate differed. Especially, it was found that development of the tip leakage vortex was dependent on the inlet casing geometry and the flow rate. This tendency is analogous to that observed between the appearance of rotating cavitation and the casing geometry and flow rate in cavitation tunnel tests. This result strongly implies that the tip leakage vortex is responsible for the appearance of rotating cavitation. By adding a gutter to the inlet casing, it was found that backflow was completely confined to the gutter regardless of flow rates. This numerical result implies that the volume of cavity generated in the backflow region should be stable despite a change of the flow rate, resulting in the suppression of increase of the mass flow gain factor. This result also supports the experimental result that cavitation surge was effectively suppressed using such a casing with a gutter.
The Effects of Splitter Plates on Turbulent Boundary Layer on a Long Flat Plate Near the Trailing Edge
Authors: Jodai Yoshifumi , Takahashi Yoshikazu , Ichimiya Masashi , Osaka Hideo
Published: May 2008

An experimental investigation has been made on a turbulent boundary layer near the trailing edge on a long flat plate. The flow was controlled by an additional splitter plate fitted to the trailing edge along the wake centerline. The length of the splitter plate, l, was varied from a half, to five times the trailing edge thickness, h. Measurements of base pressure behind the trailing edge and of mean velocity and pressure distribution in the turbulent boundary layer on the flat plate were made under the freestream zero-pressure gradient. The absolute value of the base pressure coefficient of the long flat plate was considerably smaller than that of the short flat plate without the splitter plate. A significant increase in the base pressure coefficient was achieved with the splitter plate (l∕h≧1), fitted to the long flat plate. Within an inner layer in the turbulent boundary layer near the trailing edge, the mean velocity increased more than that in the upstream position in the case without the splitter plate. With the splitter plate, however, the base pressure rise made the mean velocity distribution more closely approach that of a fully developed turbulent boundary layer.
A Moving Boundary Analysis for Start-Up Performance of a Nuclear Steam Generator
Authors: Paruya S. , Bhattacharya P.
Published: May 2008

Thermohydraulic phenomena of a steam-water natural-circulation (SWNC) system are very complicated, particularly, during its start-up and shutdown. Its performance strongly depends on the circulation inside it. Accurate quantification of the flow, void fraction, two-phase level, boiling boundary, etc., is difficult at both steady state and transient states like load variation, start-up, and shutdown. Attempts have been made to develop a high-fidelity thermohydraulic model (five-equation scheme) that caters to nonhomogeneous and thermal nonequilibrium flow to derive the dynamic effect of heating rate on the performance of the SWNC loop of steam generator of an Indian nuclear reactor during steaming-up period. The proposed work also attempts to predict boiling height, flow reversal, and density-wave oscillation (DWO). The boiling channel of the SWNC loop is modeled based on the moving boundary analysis using finite volume method. In this moving boundary problem, both control volumes of single-phase zone and two-phase zone change with time. Numerical results have been presented in this paper. The results indicate that both circulation flow variation and two-phase level variation in steam drum have strong dependency on void fraction in the boiling channel. Flow-reversal phenomenon is identified during the initial stage of boiling. Two-phase swelling and collapse that occur during the start-up are predicted. Above a critical heating rate, DWO has been observed. All these phenomena have been explained.
Design and Validation of a Scale-Adaptive Filtering Technique for LRN Turbulence Modeling of Unsteady Flow
Authors: Gyllenram W. , Nilsson H.
Published: May 2008

An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Wilcox’ original low reynolds number k-ω turbulence model. It is shown that the method is suitable for complex industrial unsteady flows in cases where full large eddy simulations (LESs) are unfeasible. During the simulation, the modeled length and time scales are compared to what can potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolvable scales, the resolvable scales will replace the modeled scales in the formulation of the eddy viscosity. The filtered k-ω model is implemented in an in-house computational fluid dynamics (CFD) code, and numerical simulations have been made of strongly swirling flow through a sudden expansion. The new model surpasses the original model in predicting unsteady effects and producing accurate time-averaged results. It is shown to be superior to the wall-adpating local eddy-viscosity (WALE) model on the computational grids considered here, since the turbulence may not be sufficiently resolved for an accurate LES. Because of the adaptive formulation, the filtered k-ω model has the potential to be successfully used in any engineering case where an LES is unfeasible and a Reynolds (ensemble) averaged Navier–Stokes simulation is insufficient.
Comment on "Absence of Cooling in New Zealand and the Adjacent Ocean During the Younger Dryas Chronozone"
Authors: Applegate Patrick J. , Lowell Thomas V. , Alley Richard B.
Published: May 2008

Barrows
et al
. (Reports, 5 October 2007, p. 86) presented cosmogenic exposure dates and data from an ocean sediment core that challenge evidence for glacier advance in New Zealand during the Younger Dryas event. We use modeling of geomorphic processes to argue that their cosmogenic exposure dates are inconclusive.
Toward an AIDS Vaccine
Authors: Walker Bruce D. , Burton Dennis R.
Published: May 2008

A quarter century of scientific discovery has been applied to developing an AIDS vaccine, yet this goal remains elusive. Specific characteristics of the virus, including the extreme genetic variability in circulating viral isolates worldwide, biological properties of HIV that impede immune attack, and a high mutation rate that allows for rapid escape from adaptive immune responses, render this a huge challenge. However, evidence of protection against AIDS viruses in animal models and control of HIV in humans under certain circumstances, together with scientific advances in understanding disease pathogenesis, provide a strong rationale and objective paths to continue the pursuit of an effective AIDS vaccine to stem the global epidemic.
Conditional Dynamics of Interacting Quantum Dots
Authors: Robledo Lucio , Elzerman Jeroen , Jundt Gregor , Atatüre Mete , Högele Alexander , Fält Stefan , Imamoglu Atac
Published: May 2008

Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled–phase gate between two solid-state qubits.
Monte Verde: Seaweed, Food, Medicine, and the Peopling of South America
Authors: Dillehay Tom D. , Ramírez C. , Pino M. , Collins M. B. , Rossen J. , Pino-Navarro J. D.
Published: May 2008

The identification of human artifacts at the early archaeological site of Monte Verde in southern Chile has raised questions of when and how people reached the tip of South America without leaving much other evidence in the New World. Remains of nine species of marine algae were recovered from hearths and other features at Monte Verde II, an upper occupational layer, and were directly dated between 14,220 and 13,980 calendar years before the present (∼12,310 and 12,290 carbon-14 years ago). These findings support the archaeological interpretation of the site and indicate that the site's inhabitants used seaweed from distant beaches and estuarine environments for food and medicine. These data are consistent with the ideas that an early settlement of South America was along the Pacific coast and that seaweeds were important to the diet and health of early humans in the Americas.
Adaptive Phenotypic Plasticity in Response to Climate Change in a Wild Bird Population
Authors: Charmantier Anne , McCleery Robin H. , Cole Lionel R. , Perrins Chris , Kruuk Loeske E. B. , Sheldon Ben C.
Published: May 2008

Rapid climate change has been implicated as a cause of evolution in poorly adapted populations. However, phenotypic plasticity provides the potential for organisms to respond rapidly and effectively to environmental change. Using a 47-year population study of the great tit (
Parus major
) in the United Kingdom, we show that individual adjustment of behavior in response to the environment has enabled the population to track a rapidly changing environment very closely. Individuals were markedly invariant in their response to environmental variation, suggesting that the current response may be fixed in this population. Phenotypic plasticity can thus play a central role in tracking environmental change; understanding the limits of plasticity is an important goal for future research.
Designers and Builders
Authors: Hughes Thomas P.
Published: May 2008

Architect and Engineer
. A Study in Sibling Rivalry.
By Andrew Saint
. Yale University Press, New Haven, CT, 2008. 552 pp. $65. ISBN 9780300124439.

Rather than a continuous narrative or theoretical analysis, this profusely illustrated exploration of the relations between architects and engineers offers six extended essays on topics ranging from the impact of military construction and organization to training in the two professions.
Development of an Immunochromatographic Lateral-Flow Device for Rapid Serodiagnosis of Invasive Aspergillosis
Authors: Thornton Christopher R.
Published: May 2008

Aspergillus fumigatus
is a cosmopolitan saprotrophic fungus that is second only to
Candida
species as a cause of invasive fungal infections in immunocompromised humans. Current immunodiagnostic tests for invasive aspergillosis (IA) are based on the detection of circulating galactomannan (GM) in a patient's serum by using a rat monoclonal antibody (MAb), EB-A2, that binds to tetra (1→5)-β-
d
-galactofuranoside, the immunodominant epitope in GM. The potential cross-reactivity of MAb EB-A2 with non-
Aspergillus
fungi, with contaminating GM in β-lactam antibiotics and foodstuffs, and with bacterial lipoteichoic acids has prompted efforts to discover non-GM antigens that can act as surrogate markers for the diagnosis of IA. This paper describes the development of a mouse MAb, JF5, that binds to a protein epitope present on an extracellular glycoprotein antigen secreted constitutively during the active growth of
A. fumigatus
. The MAb was used to develop an immunochromatographic lateral-flow device (LFD) for the rapid (15-min) detection of
Aspergillus
antigens in human serum. The test is highly specific, reacting with antigens from
Aspergillus
species but not with antigens from a large number of clinically important fungi, including
Candida
species,
Cryptococcus neoformans
,
Fusarium solani
,
Penicillium marneffei
,
Pseudallescheria boydii
, and
Rhizopus oryzae
. The LFD was able to detect circulating antigen in serum samples from patients suspected of having or shown to have IA on the basis of their clinical symptoms and results from tests for GM and fungal (1→3)-β-
d
-glucan. The ease of use of the LFD provides a diagnostic platform for the routine testing of vulnerable patients who have an elevated risk of IA.
Is the Incidence of Anaerobic Bacteremia Decreasing? Analysis of 114,000 Blood Cultures over a Ten-Year Period
Authors: Fenner Lukas , Widmer Andreas F. , Straub Clarisse , Frei Reno
Published: May 2008

The number of positive anaerobic blood culture results per 1,000 blood cultures performed decreased from 12.6 in the period from 1997 to 2001 to 7.0 in the period from 2002 to 2006 (
P
< 0.001), as did the proportion of isolated anaerobic organisms compared to the number of all organisms isolated from blood cultures (7.6% to 4.3% [
P
< 0.001]), while positive aerobic cultures remained stable. In contrast, the proportion of
Bacteroides fragilis
group members and gram-positive cocci within the anaerobic group increased (26.8% to 36.7% [
P
= 0.004] and 5.4% to 12% [
P
< 0.001], respectively). The number of patients with anaerobic bacteremia decreased from 122 patients in 1997 to 69 in 2006.
RD
Rio
Mycobacterium tuberculosis
Infection Is Associated with a Higher Frequency of Cavitary Pulmonary Disease
Authors: Lazzarini Luiz Claudio Oliveira , Spindola Silvana Miranda , Bang Heejung , Gibson Andrea L. , Weisenberg Scott , da Silva Carvalho Wania , Augusto Claudio José , Huard Richard C. , Kritski Afrânio L. , Ho John L.
Published: May 2008

Molecular genotyping has shown
Mycobacterium tuberculosis
lineages to be geographically restricted and associated with distinct ethnic populations. Whether tuberculosis (TB) caused by some
M. tuberculosis
lineages can present with a differential clinical spectrum is controversial because of very limited clinical data. We recently reported on the discovery of RD
Rio
M. tuberculosis
, a Latin American-Mediterranean sublineage that is the predominant cause of TB in Rio de Janeiro, Brazil. To investigate the clinical attributes of TB caused by RD
Rio
strains, we studied a cohort of TB cases from Belo Horizonte, Brazil, in which clinical information recorded on a standardized questionnaire was collected at the time of microbiological testing. These patients were referred for culture and drug susceptibility testing because of the clinical suspicion of “complicated” TB, as demonstrated by high rates of multidrug resistance (12%) and cavitary TB (80%). We performed spoligotyping and RD
Rio
genotyping on the
M. tuberculosis
strains and analyzed the clinical data from these patients. RD
Rio
M. tuberculosis
accounted for 37% of the total TB burden. Multivariate analysis found a significant association between TB caused by RD
Rio
strains and pulmonary cavitation and residence in Belo Horizonte. Since cavitary TB is associated with higher sputum bacillary load, our findings support the hypothesis that RD
Rio
M. tuberculosis
is associated with a more “severe” disease as a strategy to increase transmission. Future studies are needed to confirm these observations and to better define the contribution of RD
Rio
M. tuberculosis
to the global TB epidemic.
Epidemiology of Severe
Streptococcus pyogenes
Disease in Europe
Authors: Lamagni Theresa L. , Darenberg Jessica , Luca-Harari Bogdan , Siljander Tuula , Efstratiou Androulla , Henriques-Normark Birgitta , Vuopio-Varkila Jaana , Bouvet Anne , Creti Roberta , Ekelund Kim , Koliou Maria , Reinert Ralf René , Stathi Angeliki , Strakova Lenka , Ungureanu Vasilica , Schalén Claes , Jasir Aftab
Published: May 2008

The past 2 decades have brought worrying increases in severe
Streptococcus pyogenes
diseases globally. To investigate and compare the epidemiological patterns of these diseases within Europe, data were collected through a European Union FP-5-funded program (Strep-EURO). Prospective population-based surveillance of severe
S. pyogenes
infection diagnosed during 2003 and 2004 was undertaken in 11 countries across Europe (Cyprus, the Czech Republic, Denmark, Finland, France, Germany, Greece, Italy, Romania, Sweden, and the United Kingdom) using a standardized case definition. A total of 5,522 cases were identified across the 11 countries during this period. Rates of reported infection varied, reaching 3/100,000 population in the northern European countries. Seasonal patterns of infection showed remarkable congruence between countries. The risk of infection was highest among the elderly, and rates were higher in males than in females in most countries. Skin lesions/wounds were the most common predisposing factor, reported in 25% of cases; 21% had no predisposing factors reported. Skin and soft tissue were the most common foci of infection, with 32% of patients having cellulitis and 8% necrotizing fasciitis. The overall 7-day case fatality rate was 19%; it was 44% among patients who developed streptococcal toxic shock syndrome. The findings from Strep-EURO confirm a high incidence of severe
S. pyogenes
disease in Europe. Furthermore, these results have identified targets for public health intervention, as well as raising awareness of severe
S. pyogenes
disease across Europe.
Novel Chromogenic Medium for Detection of Vancomycin-Resistant
Enterococcus faecium
and
Enterococcus faecalis
Authors: Cuzon Gaëlle , Naas Thierry , Fortineau Nicolas , Nordmann Patrice
Published: May 2008

Vancomycin-resistant enterococci (VRE) are becoming widespread worldwide, and the rapid identification of VRE carriers from surveillance cultures is crucial for the efficient control of their spread. We assessed a new selective chromogenic medium, chromID VRE (bioMérieux, France), that enhanced the isolation and presumptive identification of VRE directly from rectal swabs and reduced unnecessary confirmatory and time-consuming tests.
Comparison of Respiratory Virus Detection Rates for Infants and Toddlers by Use of Flocked Swabs, Saline Aspirates, and Saline Aspirates Mixed in Universal Transport Medium for Room Temperature Storage and Shipping
Authors: Walsh Paul , Overmyer Christina Lim , Pham Kiemanh , Michaelson Scott , Gofman Larisa , DeSalvia Lisa , Tran Ty , Gonzalez Diana , Pusavat James , Feola Melanie , Iacono Kathryn T. , Mordechai Eli , Adelson Martin E.
Published: May 2008

A nylon flocked swab/universal transport medium collection method developed for bacterial sexually transmitted infections was adapted to detect respiratory viruses in infants and toddlers. This method significantly outperformed the traditional use of nasal aspirates in terms of PCR-based virus detection (
P
= 0.016), and the samples were easier for clinicians to evaluate, store, and transport.
Impact of
mecA
Gene Testing and Intervention by Infectious Disease Clinical Pharmacists on Time to Optimal Antimicrobial Therapy for
Staphylococcus aureus
Bacteremia at a University Hospital
Authors: Carver Peggy L. , Lin Shu-Wen , DePestel Daryl D. , Newton Duane W.
Published: May 2008

In patients with
Staphylococcus aureus
bacteremia, intervention by infectious disease clinical pharmacists on the basis of the results of tests for
mecA
resulted in a 25.4-h reduction in the time to optimal antimicrobial therapy, from 64.7 ± 36.8 to 39.3 ± 15.5 h (
P
= 0.002), which may result in decreased mortality.
Quadruplex Real-Time PCR Assay Using Allele-Specific Scorpion Primers for Detection of Mutations Conferring Clarithromycin Resistance to
Helicobacter pylori
Authors: Burucoa Christophe , Garnier Martine , Silvain Christine , Fauchère Jean-Louis
Published: May 2008

We developed a single-vessel multiplex real-time PCR assay that detects
Helicobacter pylori
infection and identified the four existing alleles of the 23S rRNA genes of
H. pylori
—the wild-type sequence and the three mutations conferring clarithromycin resistance—using allele-specific Scorpion primers directly on biopsy specimens. The Scorpion primers combine a primer and a probe in a single molecule and are able to distinguish single-nucleotide polymorphism. Fluorescent signals, produced when the probes are annealed, are read in four channels by a SmartCycler thermocycler. The assay was first applied successfully on 4 reference and 61 clinical strains. MICs of clarithromycin were determined by the Etest method. A perfect concordance was obtained between Etest and Scorpion PCR. Mixed populations were better detected by Scorpion PCR. We examined 259 biopsies from 229 patients by culture, PCR-restriction fragment length polymorphism (RFLP), and Scorpion PCR. One biopsy, positive for culture, exhibited inhibitors for both PCR-RFLP and Scorpion PCR. Twelve biopsies were positive for PCR-RFLP and Scorpion PCR but negative for culture with concordant determination of mutations in the 23S rRNA genes by the two PCR assays. Three biopsies were positive for Scorpion PCR only. Compared to culture, the sensitivity of Scorpion PCR was 98.3% and the specificity was 92.5%. The Scorpion PCR assay provides a highly accurate, rapid, and precise method for the detection and determination of mutations conferring clarithromycin resistance to
H. pylori.