bluuebunny/crossref_metadata_2025 huggingface dataset:
Follicular dendritic cells in multicentric Castleman disease present human herpes virus type 8 (HHV8)‐latent nuclear antigen 1 (LANA1) in a proportion of cases and is associated with an enhanced T‐cell response
Authors: El‐Daly Hesham , Bower Mark , Naresh Kikkeri N.
Published: October 2009

Multicentric Castleman disease (MCD) is a rare human herpes virus type 8 (HHV8)‐associated lymphoproliferative disorder that occurs more frequently in patients infected with human immunodeficiency virus (HIV). In tissue samples, HHV8‐infected plasmablasts localise to the mantle zones of the lymphoid follicles. We revisited the immunohistological features in 25 lymph node (LN) and three spleen samples of MCD. In five (20%) LN and one (33%) spleen sample, HHV8 latent nuclear antigen 1 (LANA1) staining was also noted on the follicular dendritic cells (FDC). The HHV8‐positive FDC subgroup of patients had significantly higher numbers of CD3‐positive T cells infiltrating the follicles when compared to the HHV8‐negative FDC subgroup (P = 0.047). Furthermore, the numbers of HHV8‐positive plasmablasts and serum HHV8 viral copy numbers were lower among the HHV8‐positive FDC subgroup when compared to the HHV8‐negative FDC subgroup (not statistically significant). Our findings show, for the first time, possible ‘presentation’ of an HHV8 antigen by FDCs in MCD.
Cellular Fingerprints: A Novel Approach Using Large‐Scale Cancer Cell Line Data for the Identification of Potential Anticancer Agents
Authors: Füllbeck Melanie , Dunkel Mathias , Hossbach Julia , Daniel Peter T. , Preissner Robert
Published: October 2009

The cellular fingerprint, a novel in silico screening approach, was developed to identify new biologically active compounds in combination with structural fingerprints. To this end, high‐throughput screening (HTS) data from the National Cancer Institute have been used. To validate this method, we have selected the proapoptotic, natural compound betulinic acid (BA). Because of its antiproliferative effect on a variety of cancer cell lines, the identification of novel BA analogs is of great interest. Novel analogs have been identified and validated in different apoptosis assays. In addition, the novel approach exhibited a strong correlation between structural similarity and biological activity, so that it offers enormous potential for the identification of novel biologically active compounds.
A karyotypic study on Silene sect. Sclerocalycinae in Turkey
Authors: Yıldız Kemal , Minareci Ersin , Çırpıcı Ali
Published: October 2009

The karyology of fifteen taxa of Silene sect. Sclerocalycinae from Turkey has been investigated. Karyotype analyses has been carried out and the chromosome number of Silene caramanica, S. peduncularis, S. armena, S. laxa, S. swertiifolia, S. caesarea, S. sclerophylla, S. haradjianii and S. lycaonica have been determined for the first time. For all the taxa studied, the diploid chromosome number and the basic chromosome number were found to be 2n=24 and x=12, respectively. Except for S. chlorifolia and S. doganii, the karyomorphology of the taxa studied is here described for the first time. S. laxa was found to have the smallest chromosomes whereas the largest ones were observed in S. haradjianii. Silene chlorifolia had the highest A1 index and S. bupleuroides subsp. bupleuroides had the highest interchromosomal asymmetry coefficient (A2).
Silencing of glycolysis in muscle: experimental observation and numerical analysis
Authors: Schmitz Joep P. J. , Van Riel Natal A. W. , Nicolay Klaas , Hilbers Peter A. J. , Jeneson Jeroen A. L.
Published: October 2009

The longstanding problem of rapid inactivation of the glycolytic pathway in skeletal muscle after contraction was investigated using 31P NMR spectroscopy and computational modelling. Accumulation of phosphorylated glycolytic intermediates (hexose monophosphates) during cyclic contraction and subsequent turnover during metabolic recovery was measured in vivo in human quadriceps muscle using dynamic 31P NMR spectroscopy. The concentration of hexose monophosphates in muscle peaked 40 s into metabolic recovery from maximal contractile work at 6.9 ± 1.3 mm (mean ±s.d.; n= 8) and subsequently declined at a rate of 0.009 ± 0.001 mm s−1. It was next tested whether the current knowledge of the kinetic controls in the glycolytic pathway in muscle integrated in the Lambeth and Kushmerick computational model of skeletal muscle glycolysis explained the experimental data. It was found that the model underestimated the magnitude of deactivation of the glycolytic pathway in resting muscle, resulting in depletion of glycolytic intermediates and substrate for oxidative ATP synthesis. Numerical analysis of the model identified phosphofructokinase and pyruvate kinase as the kinetic control sites involved in deactivation of the glycolytic pathway. Ancillary 100‐fold inhibition of both phosphofructokinase and pyruvate kinase was found necessary to predict glycolytic intermediate and ADP concentrations correctly in resting human muscle. Incorporation of this information into the model resulted in highly improved agreement between predicted and measured in vivo dynamics of hexose monophosphates in muscle following contraction. We concluded that silencing of the glycolytic pathway in muscle following contraction is most likely to be mediated by phosphofructokinase and pyruvate kinase inactivation on a time scale of seconds and minutes, respectively, and is necessary to prevent depletion of vital cellular substrates.
Continuous Collision Detection of Cubic-Spline-Based Tethers in ROV Simulations
Authors: Roy André , Carretero Juan A. , Buckham Bradley J. , Nicoll Ryan S.
Published: October 2009

Improving the efficacy of the pilot remotely operated vehicle (ROV) interaction through extensive training is paramount in reducing the duration, and thus expense, of ROV deployments. To complete training without sacrificing operational windows, ROV simulators can be used. Since the ROV tether, which provides power and telemetry, will at times dominate the ROV motion, the tether must be accurately modeled over the full duration of a simulated ROV maneuver. One aspect of the tether dynamics that remains relatively untouched is the modeling of tether self-contact, contact with other tethers, or entanglement. The aim of this work is to present a computationally efficient and accurate method of detecting tether collisions. To this end, a combinatorial global optimization method is first used to determine the approximate separation distance minima locations. Then, a local optimization scheme is used to find the exact separation distances and the locations of the closest points. The first combinatorial stage increases the speed at which the minima can be found. The minimum separation distance information and its change with respect to time can then be used to continuously determine whether a collision has occurred. If a collision is detected, a contact force is calculated from the interference geometry and applied at the collision site.
Computational Techniques for Stabilized Edge-Based Finite Element Simulation of Nonlinear Free-Surface Flows
Authors: Elias Renato N. , Gonçalves Milton A. , Coutinho Alvaro L. G. A. , Esperança Paulo T. T. , Martins Marcos A. D. , Ferreira Marcos D. A. S.
Published: October 2009

Free-surface flows occur in several problems in hydrodynamics, such as fuel or water sloshing in tanks, waves breaking in ships, offshore platforms, harbors, and coastal areas. The computation of such highly nonlinear flows is challenging, since free-surfaces commonly present merging, fragmentation, and breaking parts, leading to the use of interface-capturing Eulerian approaches. In such methods the surface between two fluids is captured by the use of a marking function, which is transported in a flow field. In this work we discuss computational techniques for efficient implementation of 3D incompressible streamline-upwind/Petrov–Galerkin (SUPG)/pressure-stabilizing/Petrov–Galerkin finite element methods to cope with free-surface problems with the volume-of-fluid method (Elias, and Coutinho, 2007, “Stabilized Edge-Based Finite Element Simulation of Free-Surface Flows,” Int. J. Numer. Methods Fluids, 54, pp. 965–993). The pure advection equation for the scalar marking function was solved by a fully implicit parallel edge-based SUPG finite element formulation. Global mass conservation is enforced, adding or removing mass proportionally to the absolute value of the normal velocity of the interface. We introduce parallel edge-based data structures, a parallel dynamic deactivation algorithm to solve the marking function equation only in a small region around the interface. The implementation is targeted to distributed memory systems with cache-based processors. The performance and accuracy of the proposed solution method is tested in the simulation of the water impact on a square cylinder and in the propagation of a solitary wave.
Experimental and Numerical Investigations on Unstiffened Tubular T-Joints of Offshore Platforms
Authors: Thandavamoorthy T. S.
Published: October 2009

This paper presents the failure pattern, the ultimate strength, and the stress concentration factor of unstiffened T-joints obtained from experimental and numerical investigations conducted on them under axial brace compression loading. The numerical modeling was performed on the whole joint using ANSYS software package. This modeling has predicted the ultimate strength accurately when compared with that of the conventional modeling of only a portion of the joint. The nominal diameter and thickness of the chord of the unstiffened T-joints were 324 mm and 12 mm, respectively, and the corresponding values of the brace were 219 mm and 8 mm, respectively. The T-joint was approximately one-fourth the size of the largest joints in the platforms built in a shallow water depth of 80 m in the Bombay High field. The bending of the whole chord member combined with punching shear failure due to its ovalization was observed to be the predominant behavior of the unstiffened joint. The numerical analysis has simulated the behavior of the joint as was observed in the experiment and has also helped establish its correct failure pattern. It was also observed in these investigations that the unstiffened joint was stiffer in ovalization mode than in flexural deflection. The results obtained from the numerical modeling were observed, in general, to be in good agreement with that obtained from the testing. The stress concentration factor predicted by the numerical analysis is in close agreement with that measured in the experiment as well as that computed using well established parametric equations.
Fatigue Capacity of Load Carrying Fillet-Welded Connections Subjected to Axial and Shear Loading
Authors: Lotsberg Inge
Published: October 2009

The status on current design recommendations concerning the fatigue capacity of load carrying fillet welds was presented by Maddox (Maddox, S., 2006, “Status Review on Fatigue Performance of Fillet Welds,” Proceedings of the OMAE Conference, Hamburg, Germany, Jun., Paper No. OMAE2006-92314) based on a literature survey. In order to examine the validity of the recommendations and to supplement the fatigue test database, a test matrix with 33 specimens was developed. This included 8 simple fillet-welded cruciform joints that were subjected to axial loading and 25 fillet-welded tubular specimens that were subjected to axial load and/or torsion for simulation of a combined stress condition in the fillet weld. The data obtained from these fatigue tests are presented in this paper. The test data are also compared with design guidance from IIW (1996, Fatigue Design of Welded Joints and Components: Recommendations of IIW Joint Working Group XIII-XV, A. Hobbacher, ed., Abington Publishing, Cambridge), Eurocode 3 (1993, Eurocode 3: Design of Steel Structures—Part 1–1: General Rules and Rules for Buildings), and DNV-RP-C203 (DNV, 2005, DNV-RP-C203, Fatigue Strength Analysis of Offshore Steel Structures).
Nonlinear Dynamics and Internal Resonances of a Ship With a Rectangular Cross-Section in Head Seas
Authors: Kleiman A. , Gottlieb O.
Published: October 2009

Finite amplitude dynamics of ships in head seas due to parametric instabilities is a subject of renewed interest with an increasing demand of operation in severe and variable environmental conditions. In this current study we investigate the nonlinear dynamics and internal resonances of a ship with a rectangular cross-section in head seas. We employ an asymptotic averaging method to obtain the slowly varying system evolution dynamics for the weakly nonlinear response, complemented by numerical integration in the strongly nonlinear regime. A weakly nonlinear frequency response is obtained analytically for a principal parametric resonance and a 1:1 roll—pitch internal resonance. Comparison of results with three degrees of freedom numerical simulations reveals a good fit. A strongly nonlinear numerical analysis reveals that beyond the stability thresholds, the system’s responses included quasiperiodic dynamics. This combined approach resolves both parametric instabilities and internal resonances induced for both weak and finite nonlinear interactions, and culminates with criteria for orbital stability thresholds describing the onset of quasiperiodic response and magnification of energy transfer between coupled pitch-heave and ship roll.
The New Year Wave: Spatial Evolution of an Extreme Sea State
Authors: Clauss Günther F. , Klein Marco
Published: October 2009

In the past years the existence of freak waves has been affirmed by observations, registrations, and severe accidents. Many publications investigated the occurrence of extreme waves, their characteristics and their impact on offshore structures, but their formation process is still under discussion. One of the famous real world registrations is the so called “New Year wave,” recorded in the North Sea at the Draupner jacket platform on January 1st, 1995. Since there is only a single point registration available, it is not possible to draw conclusions on the spatial development in front of and behind the point of registration, which is indispensable for a complete understanding of this phenomenon. This paper presents the spatial development of the New Year wave generated in a model basin. To transfer the recorded New Year wave into the wave tank, an optimization approach for the experimental generation of wave sequences with predefined characteristics is applied. The extreme sea state obtained with this method is measured at different locations in the tank, in a range from 2163 m (full scale) ahead of to 1470 m behind the target position—520 registrations altogether. The focus lies on the detailed description of a possible evolution of the New Year wave over a large area and time interval. It is observed that the extreme wave at the target position develops mainly from a wave group of three smaller waves. The group velocity, wave propagation, and the energy flux of this wave group are analyzed, in particular.
Control of Fixed Offshore Jacket Platform Using Semi-Active Hydraulic Damper
Authors: Paul Sudip , Datta T. K. , Kapuria S.
Published: October 2009

Semi-active control of fixed offshore jacket platforms in shallow water depth using semi-active hydraulic damper (SHD) is presented. The semi-active control uses Bang Bang control algorithm to provide the required control command to the SHDs. In the control strategy, SHDs are installed in the bracings, making it an attractive proposition for the use in jacket structures. Although the main objective of providing semi-active control devices is to control the acceleration response of the deck for smooth operation and comfort condition, the reduction in base shear and displacement are also considered as important. In particular, great reduction in foundation cost can be achieved by base shear control under extreme sea state. The effectiveness of the control scheme is investigated by varying some important parameters such as the damper capacity, the maximum damping coefficient, and the distribution of dampers along the height of the structures under various sea states. A four legged steel jacket platform in a water depth of 122 m is considered as an example problem for finding out the controlled responses. Three wave conditions are considered, namely, operating wave, extreme wave, and irregular sea state. Results of the study indicate that significant control in acceleration response can be achieved by semi-active control using SHDs. Further, considerable reduction in base shear is also possible by providing SHDs of adequate capacity at the bottom-most level of the jacket.
On the Modeling of Nonlinear Waves for Prediction of Long-Term Offshore Wind Turbine Loads
Authors: Agarwal P. , Manuel L.
Published: October 2009

In the design of wind turbines—onshore or offshore—the prediction of extreme loads associated with a target return period requires statistical extrapolation from available loads data. The data required for such extrapolation are obtained by stochastic time-domain simulation of the inflow turbulence, the incident waves, and the turbine response. Prediction of accurate loads depends on assumptions made in the simulation models employed. While for the wind, inflow turbulence models are relatively well established; for wave input, the current practice is to model irregular (random) waves using a linear wave theory. Such a wave model does not adequately represent waves in shallow waters where most offshore wind turbines are being sited. As an alternative to this less realistic wave model, the present study investigates the use of irregular nonlinear (second-order) waves for estimating loads on an offshore wind turbine with a focus on the fore-aft tower bending moment at the mudline. We use a 5 MW utility-scale wind turbine model for the simulations. Using, first, simpler linear irregular wave modeling assumptions, we establish long-term loads and identify governing environmental conditions (i.e., the wind speed and wave height) that are associated with the 20-year return period load derived using the inverse first-order reliability method. We present the nonlinear irregular wave model next and incorporate it into an integrated wind-wave response simulation analysis program for offshore wind turbines. We compute turbine loads for the governing environmental conditions identified with the linear model and also for an extreme environmental state. We show that computed loads are generally larger with the nonlinear wave modeling assumptions; this establishes the importance of using such refined nonlinear wave models in stochastic simulation of the response of offshore wind turbines.
Statistics of Extreme Events in Airgap Measurements
Authors: Naess A. , Stansberg C. T. , Gaidai O. , Baarholm R. J.
Published: October 2009

The paper presents a study of the extreme value statistics related to airgap measurements on a scale model of a semisubmersible platform subjected to random waves in a wave basin. Relative wave elevation records corresponding to totally 24 h storm duration are considered, made up by 8×3 h realizations. The focus is on a comparison of two alternative methods for the prediction of extreme values from finite recordings at two different locations at the platform. One is a standard method used in the wave basin, making use of a Weibull-tail fitting procedure. The other is a novel method based on the level upcrossing function combined with an optimization procedure that allows prediction at extreme response levels. Similar results are obtained in the mean values by the two methods, while the latter shows less variability in the predictions from single 3 h records.
Nonlinear Crest,
Trough, and Wave Height Distributions in Sea States With Double-Peaked
Spectra
Authors: Arena Felice , Soares C.
Guedes
Published: October 2009

The peak to trough distributions of nonlinear high sea waves in bimodal sea states in deep water are investigated. The statistical distribution of wave height is first analyzed by considering the Boccotti’s expression, where the parameters of the distribution are calculated for some bimodal spectra of sea states recorded in the Atlantic Ocean. The nonlinear crest and trough distributions are then obtained, particularizing for two peaked spectra the second-order Fedele and Arena expression, which depends on two parameters. The results have been finally validated by means of Monte Carlo simulations of second-order random waves with bimodal spectra.
Nonlinear Internal Wave Run-Up on Impermeable Steep Slopes
Authors: Tseng I-Fan , Chen Chen-Yuan , Kuo Hui-Ming
Published: October 2009

Laboratory experiments were conducted to investigate the run-up of internal solitary waves (ISWs) on steep uniform slopes in a two-layered fluid system with a free surface. A 12 m long wave flume, which incorporated a movable vertical gate for generating ISWs, was used in the experiments. A steep uniform slope was modeled at one end of the flume. In the present study we looked at internal waves with small and large amplitudes using a steep uniform slope (from one of θ=30, 50, 60, 90, 120, and 130 deg) much longer than those previously published in the literature. Results collected from a wide range of experimental runs show that the run-up height depends on the planar slope, while the breaking depth is only antecedent to the amplitude of an ISW. The overall quantitative agreement with the linear feature aspects of the incident wave amplitude is encouraging.
Feasibility Study for Real Time Measurement of Wheel-Rail Contact Using an Ultrasonic Array
Authors: Dwyer-Joyce R. S. , Yao C. , Zhang J. , Lewis R. , Drinkwater B. W.
Published: October 2009

Failure of a wheel-rail contact is usually by wear or fatigue of either component. Both mechanisms depend on the state of stress, which in turn depends on size and location of the contact patch. In this work, the feasibility of an ultrasonic approach for measuring the contact, real time on a rail, has been evaluated. The approach is based on the physical phenomenon of ultrasonic reflection at an interface. If the wheel and rail surfaces make contact, and are under high stress, they will transmit an ultrasonic pulse. However, if there is no contact, or the contact is under low stress, then the wave is completely or partially reflected. By measuring the proportion of the wave reflected, it is possible to deduce the extent of the contact area and also estimate the pressure distribution. In a previous work (Marshall, Lewis, Dwyer-Joyce, Olofsson, and Bjorklund, 2006, “Experimental Characterisation of Wheel-Rail Contact Patch Evolution,” ASME J. Tribol., 128(3), pp. 493–504), static wheel-rail contacts were scanned using a transducer to build up a two-dimensional (2D) map of the contact. The procedure was time consuming and could in no way be used for measurements online. In this work, a method is presented that could be used at line speeds, and so provide wheel-rail contact measurements in field trials. The scan is achieved by using an array transducer that performs a one dimensional electronic line scan. This, coupled with the speed of travel of the contact patch past the sensor location, enables a 2D map of the contact to be produced. Specimens were cut from wheel and rail sections and loaded together hydraulically in a biaxial frame. An array transducer was mounted beneath the rail specimen. The array transducer consisted of 64 ultrasonic elements that could be pulsed independently, simultaneously, or with controlled phase difference. The signals were reflected back from the contact to effectively produce a line scan. The transducer was physically moved to simulate the translation of the contact patch and so generate a series of 2D reflection profiles. Contacts under a range of normal and lateral loads have been measured and compared with some simple results using a pressure sensitive film. While the map produced by ultrasonic reflection is relatively coarse, the results agree well with measurements from the pressure sensitive film. The work concludes with a discussion of how this array measurement procedure might be implemented at full line speed, and what resolution could potentially be achieved.
On the Prediction of Cavitation in Dimples Using a Mass-Conservative Algorithm
Authors: Qiu Y. , Khonsari M. M.
Published: October 2009

The Floberg–Jakobsson–Olsson cavitation theory is implemented using a mass-conservative algorithm to accurately predict the behavior of cavitation in flat surfaces enhanced with dimples. The multigrid method is used to accelerate the convergence speed. Comparison is made on different cavitation theories. The results reveal that the load-carrying capacity of dimple-enhanced surfaces is limited under the simulated conditions.
Pseudo-Nine-Point Finite Difference Method for Numerical Analysis of Lubrication
Authors: Bai Shaoxian , Peng Xudong , Meng Yonggang , Wen Shizhu
Published: October 2009

Contours of surface texture of contact faces are not always parallel to the directions of the axis in solving Reynolds equations with finite difference method, and this often induces significant pressure saw-tooth effect, which results in an unignored analysis error. In this paper, pseudo-nine-point finite difference, as a new finite difference method, is introduced to solve the lubrication numerical problem of pressure saw-tooth. Also, application is carried out in gas lubrication of hard disk systems to verify the validity of the new method. In analysis, pressure distributions and gas floating forces are calculated for two different types of sliders, and the astringency and efficiency of the new method is discussed. Numerical results show that the pseudo-nine-point finite difference method can restrain pressure saw-tooth evidently, and presents better astringency and efficiency than the traditional five-point finite difference method. With the increase in mesh density, pressure distribution and gas floating force trend to steady. Also, numerical values of the floating force agree well with the experimental ones.
Pitting Life Prediction Based on a 3D Line Contact Mixed EHL Analysis and Subsurface von Mises Stress Calculation
Authors: Zhu Dong , Ren Ning , Wang Q. Jane
Published: October 2009

Surface pitting due to contact fatigue is a major failure mode of many mechanical components, such as various gears and rolling-element bearings. Pitting life prediction, therefore, is vital to design and performance/reliability improvements. Conventional prediction methods, commonly found in industrial standards, are based on the Hertzian contact theory under the assumptions that surfaces are ideally smooth with no lubrication. Today, the trend of high power density, high reliability compact design requires the life prediction to consider severe operation conditions in mixed lubrication, and the effect of surface roughness and topography. Also, it has been well known that ductile material failures in concentrated contacts are better correlated with the subsurface von Mises stress, rather than the normal Hertzian pressure. The present study aims to develop a pitting life prediction approach for line-contact components based on a 3D line-contact mixed elastohydrodynamic lubrication (EHL) model recently developed by Ren et al. (2009, “A Three-Dimensional Deterministic Model for Rough Surface Line-Contact EHL Problems,” ASME J. Tribol., 131, p. 011501), which is capable of simulating the entire transition from full-film and mixed EHL down to dry contact of real machined rough surfaces under severe operating conditions. The pitting life evaluation employs the fatigue life model developed by Zaretsky (1987, “Fatigue Criterion to System Design, Life and Reliability,” J. Propul. Power, 3(1), pp. 76–83) and extended by Epstein et al. (2003, “Effect of Surface Topography on Contact Fatigue in Mixed Lubrication,” Tribol. Trans., 46, pp. 506–513) using the von Mises stress field calculated based on the rough surface mixed-EHL results. Sample cases are analyzed for 15 sets of transmission gears, and the life prediction results are compared with available experimental data. With optimized material constants in the life model, predicted pitting life results well agree with the test data.
Wear Characterization of Al/Ingredients MMFC
Authors: Chaturvedi Anil K. , Chandra K. , Mishra P. S.
Published: October 2009

In this study, dry sliding wear behavior of Al alloy (Al 2219) based metal matrix friction composites (AlMMFCs) incorporated with varying percentage of ingredients: silicon carbide particles (15–25 wt %SiCp) and solid lubricants with 4 wt % graphite and 1 wt % antimony trisulphide (Sb2S3) were investigated. A group of four new chemical formulations, three binary composites of Al/SiCp (Al01N, Al02N, and Al03N), and a hybrid composite of Al/SiCp/solid lubricants (Al04N) were fabricated by newly a developed “cold-hot powder die compaction” method. Physical and mechanical properties were measured as usual. To measure tribological properties, dry pin-on-disk wear tests were conducted for 1 hour at varying loads of 1 MPa and 2 MPa and at sliding speeds of 3 m/s, 5 m/s, 7 m/s, and 9 m/s. The results revealed that the incorporation of SiCp from 15 wt % to 25 wt % in binary composite, density (2.8–2.9 g/cc), apparent porosity (1.4–3.4 vol %), and hardness (78–93 BHN) were increased. For hybrid composite, density (2.9–2.76 g/cc) and hardness (93–81 BHN) were decreased with the increase in apparent porosity (3.4–4.1 vol %). It was concluded that the obtained density is higher than the reported density and the obtained apparent porosity is much lower than the reported apparent porosity by Aigbodi et al. (2007, “Effects of Silicon Carbide Reinforcement on Microstructure and Properties of Cast Al–Si–Fe/Sic Particulate Composites,” Mater. Sci. Eng., A, 447, pp. 355–360) for same composition using “double stir casting” method. The value of coefficient of friction with addition of solid lubricants increased and steady at high load and speed (2 MPa, >5 m/s).The microstructures, worn surfaces, and tribolayers are also analyzed by an optical microscope and SEM. This study overviews AlMMFCs incorporated with hard particles and solid lubricants and the new technology for producing brake lining parts from these novel materials.
Characterization of a Foil Bearing Structure at Increasing Temperatures: Static Load and Dynamic Force Performance
Authors: Kim Tae Ho , Breedlove Anthony W. , San Andrés Luis
Published: October 2009

Oil-free turbomachinery relies on gas bearing supports for reduced power losses and enhanced rotordynamic stability. Gas foil bearings (GFBs) with bump-strip compliant layers can sustain large loads, both static and dynamic, and provide damping to reduce shaft vibrations. The ultimate load capacity of GFBs depends on the material properties and configuration of the underlying bump-strip structures. In high temperature applications, thermal effects, which change the operating clearances and material properties, can considerably affect the performance of the GFB structure. This paper presents experiments conducted to estimate the structural stiffness of a test GFB for increasing shaft temperatures. A 38.17 mm inner diameter GFB is mounted on a nonrotating hollow shaft affixed to a rigid structure. A cartridge heater inserted into the shaft provides a controllable heat source and thermocouples record the temperatures on the shaft and GFB housing. For increasing shaft temperatures (up to 188°C), increasing static loads (0–133 N) are applied to the bearing and its deflection recorded. In the test configuration, thermal expansion of the GFB housing, larger than that of the shaft, nets a significant increase in radial clearance, which produces a significant reduction in the bearing’s structural stiffness. A simple physical model, which assembles the individual bump stiffnesses, predicts well the measured GFB structural stiffness. Single frequency periodic loads (40–200 Hz) are exerted on the test bearing to identify its dynamic structural stiffness and equivalent viscous damping or a dry-friction coefficient. The GFB dynamic stiffness increases by as much as 50% with dynamic load amplitudes increasing from 13 N to 31 N. The stiffness nearly doubles from low to high frequencies, and most importantly, it decreases by a third as the shaft temperature rises to 188°C. In general, the GFB dynamic stiffness is lower than its static magnitude at low excitation frequencies, while it becomes larger with increasing excitation frequency due apparently to a bump slip-stick phenomenon. The GFB viscous damping is inversely proportional to the amplitude of the dynamic load, excitation frequency, and shaft temperature. The GFB dry-friction coefficient decreases with increasing amplitude of the applied load and shaft temperature, and increases with increasing excitation frequency.
Experimental and Analytical Studies on Flexure Pivot Tilting Pad Gas Bearings With Dampers Applied to Radially Compliant Pads
Authors: Rimpel Aaron , Kim Daejong
Published: October 2009

Hydrodynamic flexure pivot tilting pad gas bearings (FPTPGBs) can enable successful operation of oil-free microturbomachinery and FPTPGBs with radially compliant pads permit rotor centrifugal and/or thermal growth to exceed original bearing clearances and achieve higher speeds. This work presents the experimental and analytical study of such bearings and the application of dampers behind the pad radial compliance structure. A time domain orbit simulation method was implemented as the primary analysis tool to predict the rotor-bearing response to imbalance, the presence and location of critical speeds, etc., and to compare with test results. Experiments demonstrate the stable hydrodynamic operation of FPTPGBs with an ∼28.6 mm, 0.8 kg rotor above 120 krpm, for the first time. The rotor-bearing system was intentionally destabilized in tests by increasing bearing clearances and the viscoelastic dampers added behind the FPTPGB pads delayed the onset of subsynchronous vibrations (from 43 krpm without damper to above 50 krpm with damper). Midrange subsynchronous vibrations of the destabilized system initiated at ∼20 krpm were suppressed by ∼25 krpm due to the stabilizing effect of rotor centrifugal growth. The viscoelastic dampers had a negligible effect on suppressing these midrange subsynchronous vibrations in experiments, but this was not demonstrated in simulations, presumed to be due to much lower stiffness contribution of the damper at lower frequencies.
Optimization of Groove Geometry for a Thrust Air Bearing According to Various Objective Functions
Authors: Hashimoto Hiromu , Namba Tadashi
Published: October 2009

Grooved thrust air bearings are widely used to support high-speed, low-loaded shafts in many rotating systems because of their low friction, noiseless operation, and simple structure. Several types of groove geometries, such as straight line, spiral, and herringbone, are commonly used in actual applications. Among these, the spiral groove is mainly used. However, as far as the authors know, there is no theoretical evidence that the spiral groove is the most optimized groove geometry in all possible groove geometries. This paper describes the optimum design for the groove geometry of thrust air bearings according to various objective functions such as air film thickness, bearing torque, dynamic stiffness of air film, and other similar combinations. In an optimum design, groove geometries are expressed by the third degree of spline function, and sequential quadratic programming is used as the optimization method. It is understood that the groove geometry for optimizing air film thickness or friction torque takes the basic form of spiral groove geometry. The geometry design for optimizing the dynamic stiffness is the modified spiral groove. Numerical results are compared with the measured data, and good agreements can be seen between them.
Composite Structure Design of O-Rings Using Material Behavior to Decrease Strain Energy and Permanent Deformation
Authors: Maciejewski Nicholas J. , Sefkow Ryan B. , Klamecki Barney E.
Published: October 2009

The performance of elastomeric seals degrades over time in use due to the development of permanent material deformation. The existence of localized high stress regions below seal-housing contact areas led to consideration of improving O-ring design by modifying material behavior to decrease strain energy, and so permanent deformation, in these regions. Photoelastic stress analysis was used to experimentally characterize the stress and strain fields in O-ring sections and to validate finite element models used in design studies. O-ring section designs that included small inset regions of different material behavior than the larger surrounding section were investigated with the intent of manipulating and reducing the strain energy content. Finite element models of O-rings were used to characterize the strain energy content and distribution for inset materials with various stress-strain behaviors. Measurements of permanent deformation and load-deflection behavior of specimens held under applied compression over time showed dependence of the amount of permanent deformation on strain energy. Design rules were extracted from results of studies in which inset region material stiffness, stress-strain behavior, size, and location in the larger section were varied. O-ring sections with regions of less stiff material result in lower strain energy and more uniform strain energy density distribution than the typical one-material seal. Inclusion of less stiff softening stress-strain behavior material insets in the larger O-ring section produced reduction in strain energy level and favorable redistribution of the high strain energy density regions compared with the conventional one-material one-material-behavior design. Similar concepts will apply to the design of other elastomeric structures in which permanent material deformation affects structure performance.
Improving the Long-Term Performance of Elastomeric Seals by Material Behavior Design
Authors: Sefkow Ryan B. , Maciejewski Nicholas J. , Klamecki Barney E.
Published: October 2009

Previously it was shown that including smaller inset regions of less stiff material in the larger O-ring section at locations of high stress results in lower strain energy density in the section. This lower energy content is expected to lead to improved long-term seal performance due to less permanent material deformation and so less loss of seal-housing contact pressure. The shape of the inset region, the time-dependent change in material properties, and hence change in seal behavior over time in use were not considered. In this research experimental and numerical simulation studies were conducted to characterize the time-dependent performance of O-ring section designs with small inset regions of different mechanical behaviors than the larger surrounding section. Seal performance in terms of the rate of loss of contact pressure of modified designs and a baseline elastic, one-material design was calculated in finite element models using experimentally measured time-dependent material behavior. The elastic strain energy fields in O-ring sections were calculated under applied pressure and applied displacement loadings. The highest stress, strain, and strain energy regions in O-rings are near seal-gland surface contacts with significantly lower stress in regions of applied pressure. If the size of the modified region of the seal is comparable to the size of the highest energy density region, the shape of the inset is not a major factor in determining overall seal section behavior. The rate of loss of seal-housing contact pressure over time was less for the modified design O-ring sections compared with the baseline seal design. The time-dependent performance of elastomeric seals can be improved by designing seals based on variation of mechanical behavior of the seal over the seal section. Improvement in retention of sealing contact pressure is expected for seal designs with less stiff material in regions of high strain energy density.
Closed-Form Equations for Three Dimensional Elastic-Plastic Contact of Nominally Flat Rough Surfaces
Authors: Sepehri Ali , Farhang Kambiz
Published: October 2009

Approximate closed-form equations governing the shoulder-shoulder contact of asperities are derived based on a generalization by Chang, Etsion, and Bogy. The work entails the consideration of asperity shoulder-shoulder contact in which the volume conservation is assumed in the plastic flow regime. Shoulder-shoulder asperity contact gives rise to a slanted contact force comprising tangential and normal components. Each force component comprises elastic and plastic terms, which upon statistical summation yields the force component for the elastic and plastic forces for the contact of two rough surfaces. Half-plane tangential force due to elastic-plastic contact is derived through the statistical summation of tangential force component along an arbitrary tangential direction. Two sets of equations are found. In the first set of equations the functional forms are simpler and provide approximation of contact force to within 9%. The second set is enhanced equations derived from the first set of approximate equations that achieve an accuracy of within 0.2%.
Characteristics of Micro Gas Journal Bearings Based on Effective Viscosity
Authors: Zhang Haijun , Zhu Changsheng , Yang Qin
Published: October 2009

According to the first order slip velocity boundary, a modified Reynolds equation for micro gas journal bearings is presented with consideration of effective viscosity under a rarefied flow condition. A modified Reynolds equation is attained and solved using the finite difference method. The nondimensional pressure, load capacity, and attitude angle for micro gas journal bearings under different reference Knudsen numbers (the ratio of ambient molecular mean free path to the average radial clearance), bearing numbers, and eccentricity ratios are obtained. The numerical analysis demonstrates that the slip model with effective viscosity is in a better agreement with the FK model derived by Fukui and Kaneko than that without effective viscosity. When the bearing number is constant, the pressure and load capacity decrease, and the attitude angle changes inversely with the increasing reference Knudsen number. The larger the eccentricity ratio, the larger change in attitude angle from effective viscosity. When eccentricity ratio is less than 0.6, the attitude angle changes softly, and the effect of effective viscosity is unobvious. When the eccentricity ratio is constant, the influence of effective viscosity on nondimensional load capacity and attitude angle becomes larger with the increasing bearing number, and the influence is more prominent with a larger reference Knudsen number.
Self-assembled monolayers of poly(ethylene glycol) siloxane as a resist for ultrahigh-resolution electron beam lithography on silicon oxide
Authors: Gao Bo , Bernstein Gary H. , Lieberman Marya
Published: October 2009

Self-assembled monolayers of 2-[methoxypoly(ethyleneoxy)propyl]-trimethoxysilane (Si-PEG) reduce the nonspecific binding between silicon oxide surfaces and a variety of biomolecules. The film can be patterned by electron beam lithography at 30nm resolution. Optimal electron beam lithography exposure conditions are 4nC∕cm at 75keV. Exposed regions of the PEG film become negatively charged and less resistant to biomolecule binding, which leads to selective adhesion of biomolecules. The patterned film acts as a template for biomolecule attachment, while the intact PEG background is strongly resistant to nonspecific binding. Binding selectivities of up to 26:1 were observed for patterning cowpea mosaic virus, Salmonella phage P22 tailspike protein and poly(lysine) at 30nm linewidths.
Effect of etch-clean delay time on post-etch residue removal for front-end-of-line applications
Authors: Vos Ingrid , Hellin David , Vereecke Guy , Pavel Elizabeth , Boullart Werner , Vertommen Johan
Published: October 2009

The benefits of integrating wet clean with plasma dry etch processes have been investigated. The studied applications included shallow trench isolation (STI), hardmask-based poly-silicon (poly-Si) gate, and nickel silicide (NiSi) contact etch. In particular, the novel technology Confined Chemical Cleaning™ has been evaluated using diluted hydrofluoric acid or an ammonia hydroxide–hydrogen peroxide mixture at short and controlled exposure times on the order of seconds. It was observed that the ability to remove post-etch residues using the same wet clean process diminished with increasing delay time between etch and clean, in the timescale of hours. In addition, a detrimental effect on the electrical performance was observed for the contact application. As shown, applying stronger cleaning conditions is one solution to remove residues (STI and poly-Si gate) or to restore the electrical performance (contact). However, the more aggressive residue removal process resulted in a higher substrate loss. The mechanism of the delay effect for the poly-Si gate application has been investigated. Evaluation of the post-etch residues using thermodesorption mass spectrometry revealed that post-etch residues were primarily inorganic in nature. Interaction of the post-etch residue and/or substrate with water vapor from the ambient environment is at the origin of the observed delay effects. The mechanism proposed is a hydrolysis of oxychlorine bound in the top layer of the residue, in combination with the dissolution of SiO2 residue material into silicic acid, resulting in a strengthening of the SiO2 network structure and hence increased resistance to wet cleaning. For the contact application, the electrical degradation of the contact resistance under “no clean” or “delayed clean” conditions was correlated with the presence of an oxide layer at the metallic barrier/NiSi interface. This interfacial layer was not present for wafers with the integrated clean, which showed low contact resistances and high yield.
Diagnostics and modeling of CH4–CO2 plasmas for nanosmooth diamond deposition: Comparison to experimental data
Authors: Gries T. , Vandenbulcke L. , de Persis S. , Aubry O. , Delfau J. L.
Published: October 2009

Microwave plasma-assisted chemical vapor deposition of very smooth diamond coatings is an important process for various applications including mechanical and micromechanical systems and acoustic wave devices. Nanosmooth coatings have been deposited from CH4–CO2 gas mixtures at moderate temperature, the order of 600 °C. In order to increase the knowledge of the process and the control of the final characteristics of the films, a modeling of these plasmas is necessary. This has been carried out here from the prior determination of the plasma parameters. Optical emission spectroscopy was used in order to determine the gas kinetic temperature. Microwave interferometry and Langmuir double probe were used to determine the electron density and the electron temperature, respectively. All these experimental data have been obtained for a wide range of external parameters, such as the inlet composition, the pressure, the gas flow rate, and the power injected in the plasma. Then modeling of CH4–CO2 plasmas was developed by coupling chemical kinetics with a two-dimensional description of hydrodynamics and a surface-wall recombination of main radicals. The kinetic description of the CH4–CO2 plasmas was done by combining a specific mechanism of dissociation by electrons to a slightly modified version of a combustion mechanism for neutral-neutral interactions. This model has been validated by comparing the calculated species concentrations and the experimental results obtained by molecular beam mass spectrometry as a function of various external parameters. The influence of the inlet composition at three microwave power densities has been especially emphasized here. The calculations are in good agreement with the experimental results. It is shown that among the various parameters that influence the diamond growth from CH4–CO2 plasmas, the power density injected in the plasma is very important as it changes strongly the degree of completion of the chemical system and then the deposition conditions.