bluuebunny/crossref_metadata_2025 huggingface dataset:
DYNLL/LC8: a light chain subunit of the dynein motor complex and beyond
Authors: Rapali Péter , Szenes Áron , Radnai László , Bakos Anita , Pál Gábor , Nyitray László
Published: July 2011

The LC8 family members of dynein light chains (DYNLL1 and DYNLL2 in vertebrates) are highly conserved ubiquitous eukaryotic homodimer proteins that interact, besides dynein and myosin 5a motor proteins, with a large (and still incomplete) number of proteins involved in diverse biological functions. Despite an earlier suggestion that LC8 light chains function as cargo adapters of the above molecular motors, they are now recognized as regulatory hub proteins that interact with short linear motifs located in intrinsically disordered protein segments. The most prominent LC8 function is to promote dimerization of their binding partners that are often scaffold proteins of various complexes, including the intermediate chains of the dynein motor complex. Structural and functional aspects of this intriguing hub protein will be highlighted in this minireview.
TDP‐43: the relationship between protein aggregation and neurodegeneration in amyotrophic lateral sclerosis and frontotemporal lobar degeneration
Authors: Baloh Robert H.
Published: July 2011

Accumulations of aggregated proteins are a key feature of the pathology of all of the major neurodegenerative diseases. Amyotrophic lateral sclerosis (ALS) was brought into this fold quite recently with the discovery of TDP‐43 (TAR DNA binding protein, 43 kDa) inclusions in nearly all ALS cases. In part this discovery was fueled by the recognition of the clinical overlap between ALS and frontotemporal lobar degeneration, where ubiquitinated TDP‐43 inclusions were first identified. Later the identification of TDP‐43 mutations in rare familial forms of ALS confirmed that altered TDP‐43 function can be a primary cause of the disease. However, the simple concept that TDP‐43 is an aggregation‐prone protein that forms toxic inclusions capable of promoting neurodegeneration has not been upheld by initial investigations. This review discusses observations from human pathology, cell culture and animal model systems, to highlight our somewhat murky understanding of the relationship between TDP‐43 aggregation and neurodegeneration.
TDP‐43: new aspects of autoregulation mechanisms in RNA binding proteins and their connection with human disease
Authors: Buratti Emanuele , Baralle Francisco E.
Published: July 2011

The maintenance of correct protein homeostasis (‘proteostasis’) is an essential activity of mammalian cells to preserve their vital properties and functions. Because of its importance, correct proteostasis is achieved by the cell in several ways and at several levels of each gene expression pathway. In many cases, mRNA‐autoregulatory pathways based on a variety of feedback mechanisms have been observed to play a major role in keeping their concentration under control. This is especially true for RNA binding proteins because of their potential ability to bind their own pre‐mRNA molecules, and in particular for two subsets of nuclear factors that are commonly referred to as heterogeneous ribonucleoproteins and serine–arginine‐rich proteins. Regarding the mechanism, nonsense‐mediated RNA degradation triggered by alternative splicing of their own messenger RNA is a very common autoregulation pathway to maintain constant expression levels within the cellular environment. Recently, however, alternative mechanisms other than nonsense‐mediated decay have also been described to play a role for other RNA binding protein factors: serine–arginine‐rich splicing factor 1 (SRSF1) and transactive response DNA binding protein 43 kDa (TDP‐43). The aim of this minireview will be to discuss these old and new autoregulatory processes and their implication in disease development.
TDP‐43 and FUS/TLS: cellular functions and implications for neurodegeneration
Authors: Fiesel Fabienne C. , Kahle Philipp J.
Published: July 2011

TDP‐43 (transactive response binding protein of 43 kDa) and FUS (fused in sarcoma) comprise the neuropathological protein aggregates of distinct subtypes of the neurodegenerative diseases frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Moreover, the genes encoding TDP‐43 and FUS are linked to these diseases. Both TDP‐43 and FUS contain RNA binding motifs, and specific targets are being identified. Potential actions of TDP‐43 and FUS include transcriptional regulation, mRNA processing and micro RNA biogenesis. These activities are probably modulated by interacting proteins in cell type specific manners as well as distinctly within the nucleus and cytosol, as both proteins shuttle between these compartments. In this minireview the specific functions of TDP‐43 and FUS are described and discussed in the context of how TDP‐43 and FUS may contribute to the pathogenesis of frontotemporal lobar degeneration and amyotrophic lateral sclerosis.
Assessing changes in numbers and distribution of large whale entanglements in Newfoundland and Labrador, Canada1
Authors: Benjamins Steven , Ledwell Wayne , Huntington Julie , Davidson Anthony Raphael
Published: July 2011

Abstract

Entanglements of large whales in commercial fisheries in Newfoundland and Labrador, Canada, have been consistently recorded since 1979, as part of a program aimed at releasing captured animals and reducing costs to fishermen. This data set represented an opportunity to identify fisheries posing particular entanglement risks to local whale populations. Data were assessed over the periods 1979–1992 and 1993–2008, corresponding to distinct phases in fisheries distribution and intensity. Between 1979 and 2008, 1,209 large whale entanglements were recorded in Newfoundland and Labrador. These were mostly humpback whales (Megaptera novaeangliae; 80%) and minke whales (Balaenoptera acutorostrata; 15%). Dramatic declines in reported inshore whale entanglement rates were observed following the 1992 moratorium on Atlantic cod (Gadus morhua) fisheries. Recently, more entanglements have been reported further offshore, largely due to expansion of fisheries targeting snow crab (Chionoecetes opilio). For all whale species, entanglement rates and associated mortality rates varied considerably in different fishing gear. Fractions of humpback and minke whales found dead in different fishing gear differed substantially, with minke whales far more likely to be found dead than humpback whales.
Effect of deadwood position on saproxylic beetles in temperate forests and conservation interest of oak snags
Authors: BOUGET CHRISTOPHE , NUSILLARD BENOIT , PINEAU XAVIER , RICOU CHARLES
Published: July 2011

1. Intensive forestry has drastically reduced the volume of standing deadwood, even more than total deadwood volume. It has been demonstrated in boreal forests that snags have a high conservation value for many saproxylic species and that the lying or standing aspect of the deadwood makes a difference. The conservation of saproxylic beetles in the changing deadwood landscape of temperate managed forests depends on a deeper understanding of the ecological value of forest stand legacies.

2. Our study questioned whether the retention of oak snags is an important conservation concern in European temperate forests. We analysed the differences in saproxylic beetle fauna between oak snags and logs and explored the diameter effect on log–snag differences. We compared the species composition and richness of saproxylic beetle assemblages in a temperate deciduous forest. Emergence traps were set in a balanced sampling design of 22 ground‐lying logs and 22 oak snags with a range of intermediate decay stages and 2 diameter classes.

3. Oak snags yielded more individuals per volume unit and supported more species than logs, and exhibited significantly dissimilar assemblages from logs and hosted original species. Snags, especially large snags, were more interesting for rare beetle species conservation than logs. The feeding guild structure slightly differed between snags and logs. Overall, log–snag differences depended on the diameter class.

4. We confirm that saproxylic biodiversity would significantly benefit from forestry measures favouring oak snag retention (especially large snags), even though further multi‐scale studies are necessary to develop quantitative retention guidelines.
State of the Art: Treatment of Bipolar Disorders
Authors: Severus Emanuel , Schaaff Nadine , Möller Hans‐Jürgen
Published: July 2011

Bipolar disorders are lifelong lasting affective disorders, with an episodic course of the illness in most cases. The lifetime prevalence is around 2–5%, the illness usually appears in early adulthood and causes significant impairment in psychosocial functioning. This is a selective review focusing on recent developments and issues of interest in the psychopharmacological treatment of bipolar disorders. It is based primarily on the results of adequately powered, randomised, controlled trials (RCTs). These studies were systematically retrieved by means of a Medline search. The past 10 years have led to a broadening of the psychopharmacological treatment options for bipolar disorders. The proof of efficacy for the combination of fluoxetine/olanzapine as well as quetiapine in the acute treatment of bipolar I depression were important steps. While lithium remains the gold standard in the maintenance treatment of bipolar disorders, valproate, olanzapine, lamotrigine, aripiprazole, and quetiapine have been shown efficacious for this indication, with quetiapine possessing the broadest approval status of all drugs for the different treatment phases of this illness. Despite this progress there remains a huge demand regarding new compounds for nearly every area in the psychopharmacological treatment of bipolar disorders. In addition new methodological approaches regarding the proof of effectiveness in clinical practice are urgently needed.
Instability and Transition in a Separation Bubble Under a Three-Dimensional Freestream Pressure Distribution
Authors: Yaras M. I.
Published: July 2011

This paper presents measurements of the instability and transition processes in separation bubbles under a three-dimensional freestream pressure distribution. The measurements are performed on a flat plate on which a pressure distribution is imposed by a contoured surface facing the flat test-surface. The three-dimensional pressure distribution that is established on the test-surface approximates the pressure distributions encountered on swept blades. This type of pressure field produces crossflows in the laminar boundary layer upstream of the separation and within the separation bubble. The effects of these crossflows on the instability of the upstream boundary layer and on the instability, transition onset, and transition rate within the separated shear-layer are examined. The measurements are performed at two flow-Reynolds numbers and relatively low level of freestream turbulence. The results of this experimental study show that the three-dimensional freestream pressure field and the corresponding redistribution of the freestream flow can cause significant spanwise variation in the separation-bubble structure. It is demonstrated that the instability and transition processes in the modified separation bubble develop on the basis of the same fundamentals as in two-dimensional separation bubbles and can be predicted with the same level of accuracy using models that have been developed for two-dimensional separation bubbles.
Fully Cooled Single
Stage HP Transonic Turbine—Part I: Influence of Cooling Mass Flow Variations and Inlet
Temperature Profiles on Blade Internal and External
Aerodynamics
Authors: Haldeman C. W. , Dunn M.
G. , Mathison R. M.
Published: July 2011

A fully cooled turbine stage is utilized to investigate the combined effects of turbine stage cooling variation and high-pressure turbine (HPT) vane inlet temperature profile on the aerodynamics and heat transfer of the turbine stage operating at the proper design corrected conditions. Part I of this paper describes the overall experimental matrix, the influence of the cooling mass flows, and temperature profiles from an aerodynamic perspective. The measurements include internal and external pressures for the blade airfoil. Part II of this paper focuses on the influence of these parameters on the heat transfer to the blade airfoil and the stationary blade shroud. The major results show that cooling levels do not significantly affect the external pressure distributions over the majority of the blade and vane. However, aerodynamic effects of cooling levels and temperature profiles are seen for the vane and blade pressure loading on the suction surfaces. The magnitude of these effects ranges from 5% to 10% of the local measurement for the reference case, which is the uniform inlet profile with nominal cooling for this study. Inlet temperature profiles and cooling levels have comparable impacts on pressure loading, but their relative influence changes with location, and Reynolds number and corrected speed variations have the lowest impact on pressure loading changes, with changes below 5% of the local measurements. Another important result is that unlike uncooled experiments, the proper normalizing variable for pressures aft of the vane is not the inlet pressure but a “rotor reference pressure,” which adjusts the total inlet pressure by the increase in pressure resulting from the additional cooling mass flows. For the rotor, this consists primarily of the vane trailing edge cooling flows. This simplified model accounts for the effects of the vane cooling, and isolates the changes due to blade cooling. The spread of the cooling flows through the stage is important to the surface heat-flux, and has an impact on pressure loadings on the suction surface. The data establishes important guidelines for modelers of cooling flows. The changes observed on the suction side of the airfoils are real, but quite small from an engineering design perspective. Thus the pressure levels are stable and relatively independent of cooling levels, which is critical for good heat-transfer predictions.
Fully Cooled Single
Stage HP Transonic Turbine—Part II: Influence of Cooling Mass Flow Changes and Inlet
Temperature Profiles on Blade and Shroud
Heat-Transfer
Authors: Haldeman C. W. , Dunn M.
G. , Mathison R. M.
Published: July 2011

A fully cooled transonic high-pressure turbine stage is utilized to investigate the combined effects of turbine stage cooling variation and vane inlet temperature profile on heat transfer to the blades with the stage operating at the proper design corrected conditions. For this series of experiments, both the vane row and the blade row were fully cooled. The matrix of experimental conditions included varying the cooling flow rates and the vane inlet temperature profiles to observe the overall effect on airfoil heat-transfer. The data presented in Part I focused on the aerodynamics of the fully cooled turbine for a subset of the cases investigating two vane inlet temperature profiles (uniform and radial) and three different cooling levels (none, nominal, and high) for the high Reynolds number condition. This part of the paper focuses on the time-average heat-flux measurements on the blade and shroud region for the same cooling mass flow rates and vane inlet temperature profiles. The cooling effects are shown to be small and are centered primarily on the suction side of the airfoil. This relatively small influence is due to the ratio of the cooling gas to metal temperature being closer to 1 than the design value would dictate. The vane inlet temperature profile effects are more dominant, and using a net Stanton number reduction factor to compare the cases, an effect on the order of about 0.25 is demonstrated. This effect is due primarily to the change in the reference temperature used for the Stanton number calculation. The differences due to profile effects are small but observable toward the trailing edge of both the blade and rotor shroud. This data set forms an excellent baseline for heat-flux calculations, as the variation in the main input conditions are well documented and do not produce large changes in the heat-flux. It provides insight into the flow physics of an actual engine and guidelines about proper normalization of variables for a cooled turbine stage, supporting further development of computational heat-flux modeling techniques.
The Internal Structure of the Tip Leakage Vortex Within the Rotor of an Axial Waterjet Pump
Authors: Miorini Rinaldo L. , Wu Huixuan , Katz Joseph
Published: July 2011

The complex flow field in the tip region of a turbomachine rotor, including the tip leakage flow and tip leakage vortex (TLV), has been studied for decades. Yet many associated phenomena are still not understood. This paper provides detailed data on the instantaneous and phase-averaged inner structures of the tip flow and evolution of the TLV. Observations are based on series of high resolution planar particle image velocimetry measurements performed in a transparent waterjet pump fitted into an optical refractive index-matched test facility. Velocity distributions and turbulence statistics are obtained in several meridional planes inside the rotor. We observe that the instantaneous TLV structure is composed of unsteady vortex filaments that propagate into the tip region of the blade passage. These filaments are first embedded into a vortex sheet, which is generated at the suction side of the blade tip, and then they wrap around each other and roll up into the TLV. We also find that the leakage vortex induces flow separation at the casing endwall and entrains the casing boundary layer with its counter-rotating vorticity. As it propagates in the rotor passage, the TLV migrates toward the pressure side of the neighboring blade. Unsteadiness associated with vortical structures is also investigated. We notice that, at early stages of the TLV evolution, turbulence is elevated in the vortex sheet, in the flow entrained from the endwall, and near the vortex core. Interestingly, the turbulence observed around the core is not consistent with the local distribution of turbulent kinetic energy production rate. This mismatch indicates that, given a TLV section, production likely occurs at preceding stages of the vortex evolution. Then, the turbulence is convected to the core of the TLV, and we suggest that this transport has substantial component along the vortex. We observe that the meandering of vortex filaments dominates the flow in the passage and we decompose the unsteadiness surrounding the TLV core to contributions from interlaced vortices and broadband turbulence. The two contributions are of the same order of magnitude. During late stages of its evolution, TLV breakdown occurs, causing rapid broadening of the phase-averaged core, with little change in overall circulation. Associated turbulence occupies almost half the width of the tip region of blade passage and turbulence production there is also broadly distributed. Proximity of the TLV to the pressure side of the neighboring blade also affects entrainment of flow into the incoming tip region.
Prediction of Ingress Through Turbine Rim Seals—Part I: Externally Induced Ingress
Authors: Owen J. Michael , Zhou Kunyuan , Pountney Oliver , Wilson Mike , Lock Gary
Published: July 2011

Rotationally induced (RI) ingress is caused by the negative pressure (relative to the external air) inside the wheel-space of a gas turbine; this negative pressure, which is created by the rotating flow in the wheel-space, drives the ingestion of hot gas through the rim seals. Externally induced (EI) ingress is caused by the circumferential distribution of pressure created by the blades and vanes in the turbine annulus: Ingress occurs in those regions where the external pressure is higher than that in the wheel-space, and egress occurs where it is lower. Although EI ingress is the dominant mechanism for hot-gas ingestion in engines, there are some conditions in which RI ingress has an influence: This is referred to as combined ingress (CI). In Part I of this two-part paper, values of the sealing effectiveness (obtained using the incompressible orifice equations developed for EI ingress in an earlier paper) are compared with published experimental data and with the results obtained using 3D steady compressible computational fluid dynamics (CFD). Acceptable limits of the incompressible-flow assumption are quantified for the orifice model; For the CFD, even though the Mach number in the annulus reaches approximately 0.65, it is shown that the incompressible orifice equations are still valid. The results confirm that EI ingress is caused predominantly by the magnitude of the peak-to-trough circumferential difference of pressure in the annulus; the shape of the pressure distribution is of secondary importance for the prediction of ingress. A simple equation, derived from the orifice model, provides a very good correlation of the computed values of effectiveness. Using this correlation, it is possible to estimate the minimum sealing flow rate to prevent ingress without the need to know anything about the pressure distribution in the annulus; this makes the orifice model a powerful tool for rim-seal design.
Prediction of Ingress Through Turbine Rim Seals—Part II: Combined Ingress
Authors: Owen J. Michael , Pountney Oliver , Lock Gary
Published: July 2011

In Part I of this two-part paper, the orifice equations were solved for the case of externally induced (EI) ingress, where the effects of rotational speed are negligible. In Part II, the equations are solved, analytically and numerically, for combined ingress (CI), where the effects of both rotational speed and external flow are significant. For the CI case, the orifice model requires the calculation of three empirical constants, including Cd,e,RI and Cd,e,EI, the discharge coefficients for rotationally induced (RI) and EI ingress. For the analytical solutions, the external distribution of pressure is approximated by a linear saw-tooth model; for the numerical solutions, a fit to the measured pressures is used. It is shown that although the values of the empirical constants depend on the shape of the pressure distribution used in the model, the theoretical variation of Cw,min (the minimum nondimensional sealing flow rate needed to prevent ingress) depends principally on the magnitude of the peak-to-trough pressure difference in the external annulus. The solutions of the orifice model for Cw,min are compared with published measurements, which were made over a wide range of rotational speeds and external flow rates. As predicted by the model, the experimental values of Cw,min could be collapsed onto a single curve, which connects the asymptotes for RI and EI ingress at the respective smaller and larger external flow rates. At the smaller flow rates, the experimental data exhibit a minimum value of Cw,min, which undershoots the RI asymptote. Using an empirical correlation for Cd,e, the model is able to predict this undershoot, albeit smaller in magnitude than the one exhibited by the experimental data. The limit of the EI asymptote is quantified, and it is suggested how the orifice model could be used to extrapolate the effectiveness data obtained from an experimental rig to engine-operating conditions.
Minimizing Inlet Distortion for Hybrid Wing Body Aircraft
Authors: Liou Meng-Sing , Lee Byung Joon
Published: July 2011

A study of boundary-layer-ingesting flow in an upper-mounted offset inlet in NASA’s hybrid wing body transport concept for achieving environmental and performance requirements has been carried out. This study aims specifically at minimizing flow distortion stemming from the ingested low-momentum fluid to the level acceptable to the operation of fan blades. In this paper, we will focus on using a discrete adjoint method to arrive at an optimized wall geometry, which is parametrically represented by design variables, for transonic turbulent flows described by 3D Navier–Stokes equations supplemented with κ-ω-SST turbulence model. Of special interest herein is the flow physics resulting from optimization, revealing the intricate connections to the remarkable reduction in flow distortion and total pressure losses at the engine face. It is discovered that the counter-rotating vortex pair commonly seen in an S-inlet is eliminated by energizing both the core and boundary layer fluids through the change of wall shape by a series of peaks and valleys. Their exact forms, magnitudes, and locations, unknown a priori, are determined by the discrete adjoint method. The optimal shape, moreover, still holds similar level of superior performance at off-design conditions. The result may suggest a possible paradigm shift in flow control concept, away from disruptive penalty ridden devices, by properly conditioning and guiding the flow.
Heat Transfer for the Blade of a Cooled Stage and One-Half High-Pressure Turbine—Part I: Influence of Cooling Variation
Authors: Mathison R. M. , Haldeman C. W. , Dunn M. G.
Published: July 2011

Heat-flux measurements are presented for a one-and-one-half stage high-pressure turbine operating at design-corrected conditions with modulated cooling flows in the presence of different inlet temperature profiles. Coolant is supplied from a heavily film-cooled vane and the purge cavity (between the rotor disk and the upstream vane) but not from the rotor blades, which are solid metal. Thin-film heat-flux gauges are located on the uncooled blade pressure and suction surface (at multiple span locations), on the blade tip, on the blade platform, and on the disk and vane sides of the purge cavity. These measurements provide a comprehensive picture of the effect of varying cooling flow rates on surface heat transfer to the turbine blade for uniform and radial inlet temperature profiles. Part I of this paper examines the macroscopic influence of varying all cooling flows together, while Part II investigates the individual regions of influence of the vane outer and purge cooling circuits in more detail. The heat-flux gauges are able to track the cooling flow over the suction surface of the airfoil as it wraps upwards along the base of the airfoil for the uniform vane inlet temperature profile. A similar comparison for the radial profile shows the same coolant behavior but with less pronounced changes. From these comparisons, it is clear that cooling impacts each temperature profile similarly. Nearly all of the cooling influence is limited to the blade suction surface, but small changes are observed for the pressure surface. In addition to the cooling study, a novel method of calculating the adiabatic wall temperature is demonstrated. The derived adiabatic wall temperature distribution shows very similar trends to the Stanton number distribution on the blade.
Heat Transfer for the Blade of a Cooled Stage and One-Half High-Pressure Turbine—Part II: Independent Influences of Vane Trailing Edge and Purge Cooling
Authors: Mathison R. M. , Haldeman C. W. , Dunn M. G.
Published: July 2011

The independent influences of vane trailing edge and purge cooling are studied in detail for a one-and-one-half stage transonic high-pressure turbine operating at design-corrected conditions. This paper builds on the conclusions of Part I, which investigated the combined influence of all cooling circuits. Heat-flux measurements for the airfoil, platform, tip, and root of the turbine blade, as well as the shroud and the vane side of the purge cavity, are used to track the influence of cooling flow. By independently varying the coolant flow rate through the vane trailing edge or purge circuit, the region of influence of each circuit can be isolated. Vane trailing edge cooling is found to create the largest reductions in blade heat transfer. However, much of the coolant accumulates on the blade suction surface and little influence is observed for the pressure surface. In contrast, the purge cooling is able to cause small reductions in heat transfer on both the suction and pressure surfaces of the airfoil. Its region of influence is limited to near the hub, but given that the purge coolant mass flow rate is 1/8 that of the vane trailing edge, it is impressive that any impact is observed at all. The cooling contributions of these two circuits account for nearly all of the cooling reductions observed for all three circuits in Part I, indicating that the vane inner cooling circuit that feeds most of the vane film-cooling holes has little impact on the downstream blade heat transfer. Time-accurate pressure measurements provide further insight into the complex interactions in the purge region that govern purge coolant injection. While the pressures supplying the purge coolant and the overall coolant flow rate remain fairly constant, the interactions of the vane pressure field and the rotor pressure field create moving regions of high pressure and low pressure at the exit of the cavity. This results in pulsing regions of injection and ingestion.
Effect of Blade Inclination Angle on a Darrieus Wind Turbine
Authors: Castelli Marco Raciti , Benini Ernesto
Published: July 2011

This paper presents a model for the evaluation of energy performance and aerodynamic forces acting on a small helical Darrieus vertical axis wind turbine depending on blade inclination angle. It consists of an analytical code coupled to a solid modeling software capable of generating the desired blade geometry depending on the desired design geometric parameters, which is linked to a finite volume CFD code for the calculation of rotor performance. After describing and validating the model with experimental data, the results of numerical simulations are proposed on the bases of five machine architectures, which are characterized by an inclination of the blades with respect to the horizontal plane in order to generate a phase shift angle between lower and upper blade sections of 0 deg, 30 deg, 60 deg, 90 deg, and 120 deg for a rotor having an aspect ratio of 1.5. The effects of blade inclination on tangential and axial forces are first discussed and then the overall rotor torque is considered as a function of azimuthal position of the blades. Finally, the downstream tip recirculation zone due to the finite blade extension is analyzed for each blade inclination angle, achieving a numerical quantification of the influence of induced drag on rotor performance, as a function of both blade element longitudinal and azimuthal positions of the blade itself.
CFD Analysis of Flow and Heat Transfer in a Direct Transfer Preswirl System
Authors: Javiya Umesh , Chew John W. , Hills Nicholas J. , Zhou Leisheng , Wilson Mike , Lock Gary D.
Published: July 2011

The accuracy of computational fluid dynamics (CFD) for the prediction of flow and heat transfer in a direct transfer preswirl system is assessed through a comparison of CFD results with experimental measurements. Axisymmetric and three-dimensional (3D) sector CFD models are considered. In the 3D sector models, the preswirl nozzles or receiver holes are represented as axisymmetric slots so that steady state solutions can be assumed. A number of commonly used turbulence models are tested in three different CFD codes, which were able to capture all of the significant features of the experiments. A reasonable quantitative agreement with experimental data for static pressure, total pressure, and disk heat transfer is found for the different models, but all models gave results that differ from the experimental data in some respect. The more detailed 3D geometry did not significantly improve the comparison with experiment, which suggests deficiencies in the turbulence modeling, particularly in the complex mixing region near the preswirl nozzle jets. The predicted heat transfer near the receiver holes was also shown to be sensitive to near-wall turbulence modeling. Overall, the results are encouraging for the careful use of CFD in preswirl-system design.
A 3D Compressible Flow Model for Weak Rotating Waves in Vaneless Diffusers—Part II: Detailed Results
Authors: Sheng Feng , Chen Hua , Zhu Xiao-cheng , Du Zhao-hui
Published: July 2011

A 3D compressible flow model was presented in Part I of the paper to study the occurrence of weak rotating waves in vaneless diffusers of centrifugal compressors. In this paper, detailed results on the influences of flow and diffuser geometry parameters, including inlet Mach number, inlet distortion, wave number, diffuser outlet-to-inlet radius ratio, diffuser width to inlet radius ratio, and impeller backswept angle, on the rotating waves are presented. It was found that inlet spanwise distortion of radial velocity has little effects on diffuser stability, but rotating wave speed increases with the distortion. The speed also increases with inlet Mach number, so does diffuser instability. Impeller backswept improves diffuser stability and this effect increases with diffuser radius ratio. Multiple resonances were found when impeller backswept is coupled to inlet distortion of radial velocity. These resonances may have similar stabilities but with different wave speeds, suggesting that two rotating waves with different rotating speeds may occur at the same time. Diffuser width was found to have little effects on stability and on wave speed if the same maximum and same minimum values of inlet distortion of radial velocity are kept, but have some effects if the values are not kept. A comparison was also made between the present model predictions and results in open literatures, and good agreement with the experimental results than previous 2D models was achieved.
Analysis of the Variable Geometry Effect in Radial Turbines
Authors: Binder Nicolas , Le Guyader Sebastien , Carbonneau Xavier
Published: July 2011

The influence of variable geometry stators on the stage behavior is analyzed from both theoretical and experimental points of view. A theoretical analysis of the trajectory of some pressure-ratio lines in a loading-to-flow-coefficient diagram leads to the definition of a specific dimensionless parameter: the reduced section. This parameter is representative of the stator geometric configuration and is thus expected to be a good candidate to describe the variable geometry problem. From a theoretical point of view, this parameter is no less than the formal expression of the link between the geometric configuration of the stator and the behavior of the stage. An experimental approach decomposed in three phases is then led to evaluate this assessment. The results clearly demonstrate the crucial influence of the reduced section in the operating point definition. It leads to the conclusion that from a theoretical point of view, the two solutions mainly used in the industry for variable geometry stages (variation of the height or of the opening position of the stator blades) are equivalent provided that they are sanitized of their respective technological drawbacks. It has also been shown that the geometric configuration of the stator chosen to reach a specific value of the reduced section has some incidence on the efficiency of the stage. This observation gives some opportunities for optimization, for which some axis of reflection is given.
Film Cooling Effect of Rotor-Stator Purge Flow on Endwall Heat/Mass Transfer
Authors: Papa M. , Srinivasan V. , Goldstein R. J.
Published: July 2011

Mass transfer measurements on the endwall and blade suction surfaces are performed in a five-blade linear cascade with a high-performance rotor blade profile. The effects of purge flow from the wheelspace cavity entering the hot gas path are simulated by injecting naphthalene-free and naphthalene-saturated air through a slot upstream of the blade row at 45 deg to the endwall, for a Reynolds number of 6×105 based on blade true chord and cascade exit velocity, and blowing ratios of 0.5, 1, and 1.5. Oil-dot visualization indicates that with injection, a recirculation region is set up upstream of the leading edge, and the growth of the passage vortex is altered. The coolant exiting from the slot is drawn to the suction side of the blade and is pushed up along the suction surface of the blade by the secondary flow. For blowing ratios of 0.5 and 1.0, only a little coolant reaches the pressure side in the aft part of the passage. However, at a blowing ratio of 1.5, there is a dramatic change in the flow structure. Both the oil-dot visualization and the cooling effectiveness maps indicate that at this blowing ratio, the coolant exiting the slot has sufficient momentum to closely follow the blade profile and is not significantly entrained into the passage vortex. As a result, high cooling effectiveness values are obtained at the pressure side of the endwall, well into the midchord and aft portions of the blade passage.
Tribological Testing of Steel Coupons Bonded to Cu-Based Microchannel Heat Exchangers
Authors: Mei Fanghua , Meng W. J. , Hager Carl H. , Xue Liang A. , Evans Ryan D. , Doll Gary L.
Published: July 2011

Metal-based microchannel heat exchangers (MHEs) may offer a solution to thermal management required in a unlubricated bearing with ceramic or coated rolling elements. In this paper, we report results of tribological testing on steel coupons cooled by Cu-based MHEs. Low-profile Cu-based MHEs were fabricated and bonded to steel coupons, whose front faces were made to contact a crowned rotating steel ring, with and without oil lubrication. A series of tribological tests were conducted under different conditions with and without cooling. The tests collectively show that low-profile Cu-based MHEs placed in proximity of a tribological contact can be effective in removing heat generated at the contact interface, decrease the contact interfacial friction, and mitigate the amount of interfacial wear in sliding contacts, with and without oil lubrication. The present results suggest that cooling of tribological contact zones by embedding MHEs in proximity can be beneficial to tribological performance and deserves further investigations for tribological contact applications.
Analysis of Transient Contact Response of a Sub-10 Nanometer Air-Bearing Slider (Pico Glide Head) Using Empirical Mode Decomposition
Authors: Sheng Gang , He Jizhong , Duan Shanlin
Published: July 2011

The transient dynamics of a sub-10 nanometer air-bearing slider (pico glide head) are experimentally investigated using piezoelectric transducer (PZT)signal. Empirical mode decomposition is used to resolve the nonstationary and nonlinear response of the slider under short contacts at high temporal resolution at high frequencies. The results indicate that the empirical mode decomposition can clearly distinguish weak impacts between slider and defects on disk. By using the combination of the power spectrum density of the decomposed signal and Hilbert spectrum, multiple consecutive events during contact are effectively resolved, and the nonstationary and nonlinear spectrum signature of slider contact response are characterized.
Comparison of surface photovoltage behavior for n-type versus p-type GaN
Authors: Foussekis M. , Baski A. A. , Reshchikov M. A.
Published: July 2011

Using a Kelvin probe, the authors have studied changes in surface contact potential during illumination, i.e., surface photovoltage (SPV), for n- and p-type GaN films grown by hydride vapor phase epitaxy. Short ultraviolet (UV) exposures (3 s) generate a positive SPV of about 0.5 eV for n-type and a negative SPV of about −0.6 eV for p-type GaN, which is consistent with the expected surface band bending for these two surface types. The fast component of the SPV is attributed to the accumulation of photogenerated holes (n-type) or electrons (p-type) at the surface, which results in a decrease in band bending. During long UV exposures (1 h), however, slower photoinduced processes can cause the SPV signal to change as a function of the ambient conditions. For both n- and p-type GaN, UV illumination causes the adsorption of negatively charged oxygen species on the surface in air and their subsequent desorption in vacuum. It appears that this adsorbate effect is most prevalent for n-type GaN in vacuum and p-type GaN in air, with significant changes in the SPV of up to 0.3 eV (n-type) and 0.6 eV (p-type). One important difference between the GaN films is the sensitivity of p-type GaN to the illumination geometry. When the sample contacts are exposed to near-bandgap light, unexpected offsets of the SPV signal can result. If such offsets are appropriately taken into account, however, then the SPV behaviors for both n- and p-type GaN can be reasonably modeled by thermionic expressions.
A new clinical unit for digital radiography based on a thick amorphous Selenium plate: Physical and psychophysical characterization
Authors: Rivetti Stefano , Lanconelli Nico , Bertolini Marco , Acchiappati Domenico
Published: July 2011

Purpose:

Here, we present a physical and psychophysical characterization of a new clinical unit (named AcSelerate) for digital radiography based on a thick a‐Se layer. We also compared images acquired with and without a software filter (named CRF) developed for reducing sharpness and noise of the images and making them similar to images coming from traditional computed radiography systems.

Methods:

The characterization was achieved in terms of physical figures of merit [modulation transfer function (MTF), noise power spectra (NPS), detective quantum efficiency (DQE)], and psychophysical parameters (contrast‐detail analysis with an automatic reading of CDRAD images). We accomplished measurements with four standard beam conditions: RAQ3, RQA5, RQA7, and RQA9.

Results:

The system shows an excellent MTF (about 50% at the Nyquist frequency). The DQE is about 55% at 0.5 lp/mm and above 20% at the Nyquist frequency and is almost independent from exposure. The contrast‐detail curves are comparable to some of the best published data for other systems devoted to imaging in general radiography. The CRF filter influences both the MTF and NPS, but it does lead to very small changes on DQE. Also the visibility of CDRAD details is basically unaltered, when the filter is activated.

Conclusions:

As normally happens with detector based on direct conversion, the system presents an excellent MTF. The improved efficiency caused by the thick layer allows getting good noise characteristics and DQE results better (about 10% on average) than many of the computed radiography (CR) systems and comparable to those obtained by the best systems for digital radiography available on the market.
Volumetric lean percentage measurement using dual energy mammography
Authors: Ducote Justin L. , Klopfer Michael J. , Molloi S.
Published: July 2011

Purpose:

Currently, there is no accepted standard for measuring breast density. Dual energy mammography, which has demonstrated accurate measurement in phantoms, has been proposed as one possible method. To examine the use of chemical analysis as a possible means to validate breast density measurements from dual energy mammography, a bovine tissue model was investigated. Known quantities of lean and adipose tissue were compared with composition values measured from dual energy images and chemical analysis.

Methods:

Theoretical simulations were performed to assess the impact variations in breast composition would have on measurement of breast density from a single calibration. Fourteenex‐vivo tissue samples composed of varying amounts of pure lean tissue and pure adipose tissue (lean percentage) from 0 to 100%, in increments of 10%, were imaged using dual energy mammography. This was followed by chemical analysis based on desiccation, trituration, and fat extraction with petroleum ether to determine water, lipid, and protein content. The volumetric lean percentage (VLP) as measured from images (VLPI) and as derived from chemical analysis data (VLPCA) were compared with the VLP calculated from measurements of sample mass with a scale (VLPM). Finally, data from the bovine tissue model in this study were compared to compositional data from a previous report of human tissue composition.

Results:

The results from simulation suggest a substantial impact on measuring breast density is likely due to changes in anatomical breast composition. VLPI was related to the VLPM by VLPI = 1.53 VLPM + 10.0 (r2>0.99). VLPCA was related to VLPM by VLPCA = 0.76 VLPM + 22.8 (r2>0.99). VLPI was related to VLPCA by VLPI = 2.00 VLPCA − 35.6 (r2>0.99). Bovine adipose tissue was shown to be very similar to human adipose tissue in terms of water, lipid, and protein content with RMS differences of 1.2%. Bovine lean tissue was shown to be very similar to human skeletal muscle tissue and somewhat similar to human mammary gland tissue with RMS differences of 0.4 and 22.2%, respectively.

Conclusions:

The results of this study show strong linear relationships between volumetric lean percentage measurements using dual energy mammography, chemical analysis and the actual mass. Determining the existence of a relationship between VLPI and VLPCA was necessary before comparing density results from the dual energy technique to composition data from chemical analysis for samples of unknown composition.
Analyzing the impact of intrafraction motion: Correlation of different dose metrics with changes in target D95%
Authors: Waghorn Ben J. , Meeks Sanford L. , Langen Katja M.
Published: July 2011

Purpose:

A number of techniques are available to determine the dosimetric impact of intrafraction motion during intensity modulated radiation therapy (IMRT). Motion‐induced dose perturbations can be determined both computationally and experimentally using a number of different dosimetric metrics. However, these measures may lead to different conclusions regarding the clinical impact of motion. This study compares the analysis of identical dose perturbations using different dosimetric metrics. Calculated changes in target D95% are used as a reference.

Methods:

A total of 3768 motion‐encoded dose distributions were calculated for nine lung tumor patients. The motion‐encoded dose distributions were compared to static dose distributions using three dosimetric metrics: 2D γ, 3D γ, and histogram analysis. Each of these metrics was used to analyze dose perturbations both globally and within the target structure. Furthermore, the failing voxels were analyzed separately according to failure mode, i.e., under vs. over‐dosed voxels. Metrics were evaluated based on their agreement with changes in target D95%. Evaluations included the metrics' maximum average sensitivity and specificity (MASS) in detecting unacceptable deliveries, a coefficient correlated to ranking (τ), and the linear correlation coefficient, r.

Results:

Of the evaluated metrics, the histogram metric restricted to the under‐dosed voxels within the target agreed best with changes in target D95%. This metric achieved a MASS of 0.93, a τ of 0.69, and an r‐value of 0.85. In comparison, the unrestricted 2D γ metric achieved MASS = 0.77, τ = 0.40, and r = 0.67. Restricting the 2D γ test both geographically and in failure mode increased the MASS to 0.85, τ to 0.70, and the r‐value to 0.80.

Conclusions:

This study suggests that any clinical decisions based solely on an unrestricted 2D γ metric are suboptimal. A geographic and failure mode restriction can improve results. The remaining uncertainties with non‐DVH (dose volume histogram) based metrics should be kept in mind when they are used to evaluate the dosimetric impact of target motion.