bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural similarity to link sequence space: New potential superfamilies and implications for structural genomics
Authors: Aloy Patrick , Oliva Baldomero , Querol Enrique , Aviles Francesc X. , Russell Robert B.
Published: July 2002

The current pace of structural biology now means that protein three‐dimensional structure can be known before protein function, making methods for assigning homology via structure comparison of growing importance. Previous research has suggested that sequence similarity after structure‐based alignment is one of the best discriminators of homology and often functional similarity. Here, we exploit this observation, together with a merger of protein structure and sequence databases, to predict distant homologous relationships. We use the Structural Classification of Proteins (SCOP) database to link sequence alignments from the SMART and Pfam databases. We thus provide new alignments that could not be constructed easily in the absence of known three‐dimensional structures. We then extend the method of Murzin (1993b) to assign statistical significance to sequence identities found after structural alignment and thus suggest the best link between diverse sequence families. We find that several distantly related protein sequence families can be linked with confidence, showing the approach to be a means for inferring homologous relationships and thus possible functions when proteins are of known structure but of unknown function. The analysis also finds several new potential superfamilies, where inspection of the associated alignments and superimpositions reveals conservation of unusual structural features or co‐location of conserved amino acids and bound substrates. We discuss implications for Structural Genomics initiatives and for improvements to sequence comparison methods.
Quantitative evaluation of the lengths of homobifunctional protein cross‐linking reagents used as molecular rulers
Authors: Green Nora S. , Reisler Emil , Houk K.N.
Published: July 2002

Homobifunctional chemical cross‐linking reagents are important tools for functional and structural characterization of proteins. Accurate measures of the lengths of these molecules currently are not available, despite their widespread use. Stochastic dynamics calculations now provide quantitative measures of the lengths, and length dispersions, of 32 widely used molecular rulers. Significant differences from published data have been found.
Intrinsic H+ ion mobility in the rabbit ventricular myocyte
Authors: Vaughan‐Jones R. D. , Peercy B. E. , J. P. Keener  , Spitzer K. W.
Published: July 2002

The intrinsic mobility of intracellular H+ ions was investigated by confocally imaging the longitudinal movement of acid inside rabbit ventricular myocytes loaded with the acetoxymethyl ester (AM) form of carboxy‐seminaphthorhodafluor‐1 (carboxy‐SNARF‐1). Acid was diffused into one end of the cell through a patch pipette filled with an isotonic KCl solution of pH 3.0. Intracellular H+ mobility was low, acid taking 20‐30 s to move 40 μm down the cell. Inhibiting sarcolemmal Na+‐H+ exchange with 1 mm amiloride had no effect on this time delay. Net H+i movement was associated with a longitudinal intracellular pH (pHi) gradient of up to 0.4 pH units. H+i movement could be modelled using the equations for diffusion, assuming an apparent diffusion coefficient for H+ ions (DHapp) of 3.78 × 10−7 cm2 s−1, a value more than 300‐fold lower than the H+ diffusion coefficient in a dilute, unbuffered solution. Measurement of the intracellular concentration of SNARF (≈400 μM) and its intracellular diffusion coefficient (0.9 × 10−7 cm2 s−1) indicated that the fluorophore itself exerted an insignificant effect (between 0.6 and 3.3 %) on the longitudinal movement of H+ equivalents inside the cell. The longitudinal movement of intracellular H+ is discussed in terms of a diffusive shuttling of H+ equivalents on high capacity mobile buffers which comprise about half (≈11 mm) of the total intrinsic buffering capacity within the myocyte (the other half being fixed buffer sites on low mobility, intracellular proteins). Intrinsic H+i mobility is consistent with an average diffusion coefficient for the intracellular mobile buffers (Dmob) of ≈9 × 10−7 cm2 s−1.
Cytosolic Ca2+ and Ca2+‐activated Cl− current dynamics: insights from two functionally distinct mouse exocrine cells
Authors: Giovannucci David R. , Bruce Jason I. E. , Straub Stephen V. , Arreola Jorge , Sneyd James , Shuttleworth Trevor J. , Yule David I.
Published: July 2002

The dynamics of Ca2+ release and Ca2+‐activated Cl− currents in two related, but functionally distinct exocrine cells, were studied to gain insight into how the molecular specialization of Ca2+ signalling machinery are utilized to produce different physiological endpoints: in this case, fluid or exocytotic secretion. Digital imaging and patch‐clamp methods were used to monitor the temporal and spatial properties of changes in cytosolic Ca2+ concentration ([Ca2+]c) and Cl− currents following the controlled photolytic release of caged‐InsP3 or caged‐Ca2+. In parotid and pancreatic acinar cells, changes in [Ca2+]c and activation of a Ca2+‐activated Cl− current occurred with close temporal coincidence. In parotid, a rapid global Ca2+ signal was invariably induced, even with low‐level photolytic release of threshold amounts of InsP3. In pancreas, threshold stimulation generated an apically delimited [Ca2+]c signal, while a stronger stimulus induced a global [Ca2+]c signal which exhibited characteristics of a propagating wave. InsP3 was more effective in parotid, where [Ca2+]c signals initiated with shorter latency and exhibited a faster time‐to‐peak than in pancreas. The increased potency of InsP3 in parotid probably results from a four‐fold higher number of InsP3 receptors as measured by radiolabelled InsP3 binding and western blot analysis. The Ca2+ sensitivity of the Cl− channels in parotid and pancreas was determined from the [Ca2+]‐current relationship measured during a dynamic ‘Ca2+ ramp’ produced by the continuous, low‐level photolysis of caged‐Ca2+. In addition to a greater number of InsP3 receptors, the Cl− current density of parotid acinar cells was more than four‐fold greater than that of pancreatic cells. Whereas activation of the current was tightly coupled to increases in Ca2+ in both cell types, local Ca2+ clearance was found to contribute substantially to the deactivation of the current in parotid. These data reveal specializations of common modules of Ca2+‐release machinery and subsequent effector activation that are specifically suited to the distinct functional roles of these two related cell types.
Air Bearing Force Measurement of Pico Negative Pressure Sliders During Dynamic Unload
Authors: Chapin M. , Bogy D. B.
Published: July 2002

The air bearing forces of “pico negative pressure” (1.25 × 1.0 mm subambient pressure) sliders during the unload process were investigated experimentally. A high speed vertical load/unload mechanism with a sensitive force transducer was developed to measure the air bearing forces. Force histories were measured at various disk rpm and unload velocities. The force histories showed that the suspension load dimple separated from the load beam during the lifting. This separation was held to an acceptable amount by flexure limitors built into the suspension. Force-displacement curves show the need for control of the gap between the limitor and load beam. A technique was developed to determine critical suspension parameters for use in the CML Dynamic Load/Unload Simulator. Simulation of the force history was then in excellent agreement with experimental results. Both simulation and experimental results showed that the lift-off force decreases with increasing disk rpm. Experimental results also showed that higher unload speeds lead to larger lift-off forces. By selecting the correct disk rpm and unload speed, the lift-off force could be minimized. [S0742-4787(00)00103-X]
State Feedback Stabilization of an Electropneumatic System
Authors: Outbib R. , Richard E.
Published: July 2002

This paper presents a study of an electropneumatic system composed of two electropneumatic interfaces and a pneumatic cylinder. The model used is a simplified nonlinear model which takes into account the main nonlinearities. The main goal is to prove that the process with two controls can be made asymptotically stable by means of a regular (i.e., at least of class C1) state feedback. To illustrate the performances obtained, with the proposed control, simulation results are given. [S0022-0434(00)01303-4]
Experimental Investigation to Study Convective Mixing, Spatial Uniformity, and Cycle-to-Cycle Variation During the Intake Stroke in an IC Engine
Authors: Choi Woong-Chul , Guezennec Yann G.
Published: July 2002

The work described in this paper focuses on experiments to quantify the initial fuel mixing and gross fuel distribution in the cylinder during the intake stroke and its relationship to the large-scale convective flow field. The experiments were carried out in a water analog engine simulation rig, and, hence, limited to the intake stroke. The same engine head configuration was used for the three-dimensional PTV flow field and the PLIF fuel concentration measurements. High-speed CCD cameras were used to record the time evolution of the dye convection and mixing with a 1/4 deg of crank angle resolution (and were also used for the three-dimensional PTV measurements). The captured sequences of images were digitally processed to correct for background light non-uniformity and other spurious effects. The results are finely resolved evolution of the dye concentration maps in the center tumble plane. The three-dimensional PTV measurements show that the flow is characterized by a strong tumble, as well as pairs of cross-tumble, counter-rotating eddies. The results clearly show the advection of a fuel-rich zone along the wall opposite to the intake valves and later along the piston crown. It also shows that strong out-of-plane motions further contribute to the cross-stream mixing to result in a relatively uniform concentration at BDC, albeit slightly stratified by the lean fluid entering the cylinder later in the intake stroke. In addition to obtaining phase-averaged concentration maps at various crank angles throughout the intake stroke, the same data set is processed for a large number of cycle to extract spatial statistics of the cycle-to-cycle variability and spatial non-uniformity of the concentration maps. The combination of the three-dimensional PTV and PLIF measurements provides a very detailed understanding of the advective mixing properties of the intake-generated flow field. [S0742-4795(00)00103-4]
High Free-Steam Turbulence Effects on Endwall Heat Transfer for a Gas Turbine Stator Vane
Authors: Radomsky R. W. , Thole K. A.
Published: July 2002

High free-stream turbulence along a gas turbine airfoil and strong secondary flows along the endwall have both been reported to increase convective heat transfer significantly. This study superimposes high free-stream turbulence on the naturally occurring secondary flow vortices to determine the effects on the flowfield and the endwall convective heat transfer. Measured flowfield and heat transfer data were compared between low free-stream turbulence levels (0.6 percent) and combustor simulated turbulence levels (19.5 percent) that were generated using an active grid. These experiments were conducted using a scaled-up, first-stage stator vane geometry. Infrared thermography was used to measure surface temperatures on a constant heat flux plate placed on the endwall surface. Laser-Doppler Velocimetry (LDV) measurements were performed of all three components of the mean and fluctuating velocities of the leading edge horseshoe vortex. The results indicate that the mean flowfields for the leading edge horseshoe vortex were similar between the low and high free-stream turbulence cases. High turbulence levels in the leading edge–endwall juncture were attributed to a vortex unsteadiness for both the low and high free-stream turbulence cases. While, in general, the high free-stream turbulence increased the endwall heat transfer, low augmentations were found to coincide with the regions having the most intense vortex motions. [S0889-504X(00)00704-2]
Biomechanical Analysis of the Three-Dimensional Foot Structure During Gait: A Basic Tool for Clinical Applications
Authors: Gefen A. , Megido-Ravid M. , Itzchak Y. , Arcan M.
Published: July 2002

A novel three-dimensional numerical model of the foot, incorporating, for the first time in the literature, realistic geometric and material properties of both skeletal and soft tissue components of the foot, was developed for biomechanical analysis of its structural behavior during gait. A system of experimental methods, integrating the optical Contact Pressure Display (CPD) method for plantar pressure measurements and a Digital Radiographic Fluoroscopy (DRF) instrument for acquisition of skeletal motion during gait, was also developed in this study and subsequently used to build the foot model and validate its predictions. Using a Finite Element solver, the stress distribution within the foot structure was obtained and regions of elevated stresses for six subphases of the stance (initial-contact, heel-strike, midstance, forefoot-contact, push-off, and toe-off) were located. For each of these subphases, the model was adapted according to the corresponding fluoroscopic data, skeletal dynamics, and active muscle force loading. Validation of the stress state was achieved by comparing model predictions of contact stress distribution with respective CPD measurements. The presently developed measurement and numerical analysis tools open new approaches for clinical applications, from simulation of the development mechanisms of common foot disorders to pre- and post-interventional evaluation of their treatment. [S0148-0731(00)01106-7]
Geometric Simulation of Ball-End Milling Operations
Authors: Imani B. M. , Elbestawi M. A.
Published: July 2002

In this paper, B-rep solid modeling techniques are used to deal with geometric modeling issues encountered in ball-end milling simulation. The precise B-rep model of the cutter swept volume is developed using advanced sweeping/skinning techniques. Semi-finishing operations are simulated by performing consecutive Boolean operations between the updated part and swept volume. The instantaneous chip geometry is accurately and reliably extracted from the B-rep model of the updated part. Also, the material removal in ball-end milling is precisely simulated for finishing operations, in order to construct the feed-mark and scallop geometries. The validity of the final model is confirmed by comparing the predicted feed-mark profile with experimental measurements. The system developed can be used to verify and optimize NC codes, thus contributing to improving reliability, accuracy, and productivity in CNC machining.
Estimation of NOx Emissions in Thermal Power Plants Using Neural Networks
Authors: Ferretti G. , Piroddi L.
Published: July 2002

In this paper a neural network-based strategy is proposed for the estimation of the NOx emissions in thermal power plants, fed with both oil and methane fuel. A detailed analysis based on a three-dimensional simulator of the combustion chamber has pointed out the local nature of the NOx generation process, which takes place mainly in the burners’ zones. This fact has been suitably exploited in developing a compound estimation procedure, which makes use of the trained neural network together with a classical one-dimensional model of the chamber. Two different learning procedures have been investigated, both based on the external inputs to the burners and a suitable mean cell temperature, while using local and global NOx flow rates as learning signals, respectively. The approach has been assessed with respect to both simulated and experimental data.
Stability of Water-Lubricated, Hydrostatic, Conical Bearings With Spiral Grooves for High-Speed Spindles
Authors: Yoshimoto S. , Oshima S. , Danbara S. , Shitara T.
Published: July 2002

In this paper, the stability of water-lubricated, hydrostatic, conical bearings with spiral grooves for high-speed spindles is investigated theoretically and experimentally. In these bearing types, pressurized water is first fed to the inside of the rotating shaft and then introduced into spiral grooves through feeding holes located at one end of each spiral groove. Therefore, water pressure is increased due to the effect of the centrifugal force at the outlets of the feeding holes, which results from shaft rotation. In addition, water pressure is also increased by the viscous pumping effect of the spiral grooves. The stability of the proposed bearing is theoretically predicted using the perturbation method, and calculated results are compared with experimental results. It was consequently found that the proposed bearing is very stable at high speeds and theoretical predictions show good agreement with experimental data.
Energetics of Actively Powered Locomotion Using the Simplest Walking Model
Authors: Kuo Arthur D.
Published: July 2002

We modified an irreducibly simple model of passive dynamic walking to walk on level ground, and used it to study the energetics of walking and the preferred relationship between speed and step length in humans. Powered walking was explored using an impulse applied at toe-off immediately before heel strike, and a torque applied on the stance leg. Although both methods can supply energy through mechanical work on the center of mass, the toe-off impulse is four times less costly because it decreases the collision loss at heel strike. We also studied the use of a hip torque on the swing leg that tunes its frequency but adds no propulsive energy to gait. This spring-like actuation can further reduce the collision loss at heel strike, improving walking energetics. An idealized model yields a set of simple power laws relating the toe-off impulses and effective spring constant to the speed and step length of the corresponding gait. Simulations incorporating nonlinear equations of motion and more realistic inertial parameters show that these power laws apply to more complex models as well.
Boundary Optimal Control of Natural Convection by Means of Mode Reduction
Authors: Park H. M. , Lee W. J.
Published: July 2002

We consider problems of controlling the intensity of the Rayleigh-Be´nard convection by adjusting the heat flux distribution at the boundary while keeping the heat input the same. The Karhunen-Loe`ve Galerkin procedure is used to reduce the Boussinesq equation to a low dimensional dynamic model, which in turn is employed in a projected gradient method to yield the optimal heat flux distribution. The performance of the Karhunen-Loe`ve Galerkin procedure is assessed in comparison with the traditional technique employing the Boussinesq equation, and is found to be very accurate as well as efficient.
Estimating Confidence Intervals of Long Return Period Design Values by Bootstrapping
Authors: Naess A. , Hungnes B.
Published: July 2002

This paper describes a method for extrapolation of extreme value data for estimating long return period characteristic values. It is based on using yearly extreme value data subjected to a transformation which is derived from analysis of the underlying all-year data. The problem of establishing confidence intervals for the predicted return period values is discussed. It also demonstrates how the method of bootstrapping can be used for this purpose.
Some Plastic Deformation Modes for Indentation of Half Space by a
Rigid Body With Serrated Surface as a Model of Roughness Transfer in Metal
Forming
Authors: Shi Jingyu , McElwain D. L. S. , Domanti S. A.
Published: July 2002

This paper is concerned with the plastic deformation modes of the free surface of the half space between the teeth on the serrated surface of a rigid body. The rigid body indents the half space perpendicularly and the material of the half space is assumed to be elastic/rigid perfectly plastic. Plane-strain conditions are assumed. The emphasis in this paper is on the profile left on the surfaces of the material when the indentation proceeds to some depth and then the indenter is removed. Based on the observations from finite element results, slip line fields for the plastic deformation regions at various stages of indentation are proposed and the corresponding hodographs for the velocity field are presented. This has application in roughness transfer of final metal forming process.
Thermal Analysis of Multiphoton Absorption at 193 nm in Volume-Absorbing Glass
Authors: Zhang and Z. M. , Chen D. H.
Published: July 2002

Two-photon absorption in volume-absorbing materials may be significant for high-power, short-pulse excimer laser irradiation. In the present work, the effects of two-photon absorption on the laser intensity propagation and the penetration depth are investigated. The temperature history of a glass plate during pulsed ultraviolet (UV) laser heating is predicted. The results show that the two-photon absorption can compress the volume-absorbing effect to surface absorption and increase the peak temperature on the glass surface. This will reduce the damage threshold, increase the energy loss, and reduce the accuracy of pulsed-laser calorimeters.
Exact Solution for Determination of the Maximum Sublimation Rate in a
Porous Medium
Authors: Lin Sui
Published: July 2002

The optimum condition for the sublimation process taking place in a porous half space are determined in this paper. The vapor mass concentration at the surface of the porous medium and the initial frozen mass concentration in the frozen region are predetermined. The optimum condition is found by determining the vapor mass concentration at the sublimation front between the vapor and frozen phases, that yields the maximum flux of the vapor mass at the sublimation front. Exact solutions of the temperature and vapor mass concentration as well as the location of the moving sublimation front are obtained. The surface temperature used as the thermal controller is also determined to match the optimum sublimation condition.
Stagnation Line Heat Transfer Augmentation Due to Freestream
Vortical Structures and Vorticity
Authors: Oo Aung N. , Ching Chan Y.
Published: July 2002

An experimental study has been performed to investigate the effect of freestream vortical structures and vorticity on stagnation region heat transfer. A heat transfer model with a cylindrical leading edge was tested in a wind tunnel at Reynolds numbers ranging from 67,750 to 142,250 based on leading edge diameter of the model. Grids of parallel rods were placed at several locations upstream of the heat transfer model in orientations where the rods were perpendicular and parallel to the stagnation line to generate freestream turbulence with distinct vortical structures. All three components of turbulence intensity, integral length scale and the spanwise and transverse vorticity were measured to characterize the freestream turbulence. The measured heat transfer data and freestream turbulence characteristics were compared with existing empirical models for the stagnation line heat transfer. A new correlation for the stagnation line heat transfer has been developed that includes the spanwise fluctuating vorticity components.
Equilibrium Solutions and Existence for Traveling, Arbitrarily Sagged Elastic Cables
Authors: Luo A. C. J. , Mote, C. D.
Published: July 2002

The exact, closed-form, three-dimensional solutions for the steady motion of traveling, sagged, elastic cables under arbitrarily distributed and concentrated loading are developed in this paper. Three components of displacement describing two equilibrium states of an extensible traveling elastic cable are derived. These exact solutions apply to straight and sagged cables traveling under their own weight and uniformly distributed loading. The exact solutions are also used to investigate the steady motion of three-dimensional traveling cables under the uniformly distributed and concentrated loading. Traveling elastic cables with large sag can be modeled approximately through the inextensible cable model when both the loading and the translation speed are very small. A slightly sagged cable must be modeled as extensible, rather than inextensible, even though both the loading and transport speed are very small. These solutions can be applied to multispan cable structures. [S0021-8936(00)02601-5]
Microscopic Damage Mechanism of Nickel-Based Superalloy Inconel 738LC Under Creep-Fatigue Conditions
Authors: Yamamoto Masato , Ogata Takashi
Published: July 2002

Creep-fatigue damage in Inconel 738LC was clarified by in-situ observation and a new creep-fatigue life prediction model was proposed based on the mechanism identified. Creep-fatigue tests on standard specimens show that the tensile hold creep-fatigue lives were reduced to 60 to 80 percent and those in the compressive hold condition were reduced to 20 to 40 percent of the fatigue life of the same total strain condition. In-situ creep-fatigue tests on miniature specimens show that grain boundary sliding could be observed under the compressive strain hold condition and under the tensile strain hold condition grain boundary cavity damage and grain boundary sliding were observed. These mechanisms are regarded as the main cause of the damage acceleration under the creep-fatigue loading conditions. Therefore, the new creep-fatigue life prediction model, which is based on the nonlinear damage accumulation method, employed two damage acceleration parameters “dsl” and “dcr,” which represent grain boundary sliding damage and grain boundary cavity damage, respectively. Creep-fatigue lives of the test results were well predicted by the proposed model. [S0094-4289(00)01203-2]
Conceptual Basis for a New Approach to Bladed-Disk Design
Authors: Layton Richard A. , Marra John J.
Published: July 2002

A central issue in gas turbine engine design today is the demand for higher performance, greater reliability, shorter lead times, and lower cost. The design of bladed disks (fans, compressors and turbines) is one area in which suitable design tools are sought to meet this demand. In this paper is presented the conceptual basis for a new, energy-based approach to design and an outline for future development of the approach as a software-based design tool. Technical tasks and risks associated with this development are summarized. It is hoped that this study will facilitate dialogue among practitioners of the various disciplines involved in bladed-disk design. [S0742-4795(00)00302-1]
Large Eddy Simulation of Flow Past a Square Cylinder: Comparison of Different Subgrid Scale Models
Authors: Sohankar Ahmad , Davidson L. , Norberg C.
Published: July 2002

Large eddy simulation of flow past a rigid prism of a square cross section with one side facing the oncoming flow at Re=2.2×104 is performed. An incompressible code is used employing an implicit fractional step method finite volume with second-order accuracy in space and time. Three different subgrid scale models: the Smagorinsky, the standard dynamic, and a dynamic one-equation model, are applied. The influence of finer grid, shorter time step, and larger computational spanwise dimension is investigated. Some global quantities, such as the Strouhal number and the mean and rms values of lift and drag, are computed. A scheme for correcting the global results for blockage effects is presented. By comparison with experiments, the results produced by the dynamic one-equation one give better agreement with experiments than the other two subgrid models. [S0098-2202(00)01001-4]
Critical Heat Flux During Natural Circulation Boiling of Saturated
Liquid in Annulus With Uniformly Heated Outer Tube
Authors: Monde M. , Mitsutake Y.
Published: July 2002

Critical heat flux has been measured during natural circulation boiling of water and R113 on a uniformly heated outer tube in a vertical annular tube. The experiment was carried out using water at atmospheric pressure and R113 at a pressure of 0.1–0.4 MPa for the annular gap width of S=1.0-4.0 mm, the heated tube diameter of 9–17 mm, and the annular tube length of 100–1000 mm. The similarity of critical heat flux between annular configurations of either inner or outer heated tubes and a simple heated tube can be clearly elucidated based on the characteristics of the heated equivalent diameter. The critical heat flux measured for S=1 mm can be predicted accurately by existing correlation for the annular tube and for clearance larger than S=4 mm by existing correlation for the single tube. A new correlation for medium clearances from S=1 to 4 mm has been developed to connect between both the existing correlations. [S0022-1481(00)01901-0]
Reliability Analysis of Pipelines During Laying, Considering Ultimate
Strength Under Combined Loads
Authors: Igland Ragnar T. , Moan Torgeir
Published: July 2002

Structural reliability methods are applied to establish a measure of safety for pipelines during laying, and especially to calibrate semi-probabilistic ultimate limit state criteria based on measures of uncertainty, method of reliability, and a given target level. Ultimate collapse of thick tubes under combined external pressure, tension, and bending loads are studied applying the finite element method. Nonlinear effects of large deformations, effects of initial ovality, residual stresses, strain-hardening, yield anisotropy, and loading paths were accounted for in the analysis. A set of interaction equations is proposed. Load effects in the pipelines during installation by the S-lay method are studied. The effects of uncertainties in yield stress, mass, stiffness of the stinger, response amplitude operator and peak period for the wave spectrum were accounted for in the analysis. The major factors affecting strain concentration due to concrete coating are taken into account. A combination of design point calculation and importance sampling procedure is used to calculate the probability of failure. The study includes calibration of partial safety factors for the design format selected. The most important random variable is the model uncertainty for bending capacity, while the uncertainty of the load effect has minor importance for the probability of failure. The system effect is taken into account considering the correlation along the pipeline. The probability of failure is referred both to the total laying period as well as a 3-h period demonstrating that the target level needs to be defined in view of the reference time period. [S0892-7219(00)01501-6]
Titanium Drilling Risers—Application and Qualification
Authors: Salama Mamdouh M. , Murali Jagannathan , Joosten Mike W.
Published: July 2002

Titanium alloy Ti-6AI-4V ELI is selected for a high-pressure drilling riser application due to its high specific strength, corrosion resistance, and favorable elastic properties. The qualification of this titanium alloy requires assessing its resistance to hydrogen embrittlement and stress corrosion cracking due to seawater with/without cathodic protection, evaluating its wear resistance against a rotating steel drill string, and studying the influence of service-induced defects on fatigue and crack growth behavior when subjected to the operating environment. The paper presents an overview of the design requirements for a titanium drilling riser, and the material properties of the Ti-6AI-4V ELI alloy proposed for this application. The paper also highlights recent efforts to merge titanium and composite technologies to develop cost-effective drilling risers. [S0892-7219(00)01001-3]
Comparative Assessment of Hydrodynamic Models in Slow-Motion Mooring
Dynamics
Authors: Matsuura João Paulo J. , Nishimoto Kazuo , Bernitsas Michael M. , Garza-Rios Luis O.
Published: July 2002

The slow-motion dynamics of a turret mooring system is analyzed and compared for four of the most commonly used ship hydrodynamic maneuvering models. Each of those utilizes a different approach to model and then to calculate or measure the hydrodynamic forces and moment acting on the vessel. The four hydrodynamic maneuvering models are studied first by a physics-based analysis of each model and then by numerically comparing their prediction of equilibria, nonlinear stability analysis, bifurcation sequences, and morphogeneses of turret mooring systems. Catastrophe sets are constructed in two-dimensional parametric design spaces to determine the qualitative behavior of the system, and nonlinear time simulations are used to assess its quantitative properties. Static bifurcations of the principal equilibrium are compared to determine the nature of alternate equilibria. A turret-moored tanker is modeled with anchored catenaries, including nonlinear drag. External excitation is time independent, and for the numerical applications it is limited to steady current. Of the four models used, the Abkowitz and Takashina models show similar qualitative dynamics. The Obokata and Short-Wing models are also qualitatively similar, but very different from the first group. Limited sensitivity analysis pinpoints the source of discrepancy between the two schools of thought. [S0892-7219(00)01401-1]
Assessment and Repair of Offshore Platform Applications to Bay of
Campeche Facilities
Authors: Bayazitoglu Yildirim O.
Published: July 2002

In 1995 hurricanes Opal and Roxanne passed through Bay of Campeche (BOC). Opal did not cause any noticeable damage. Roxanne, on the other hand, was the most severe hurricane recorded in the Bay of Campeche in this century. Its anomalous behavior and the resulting extreme environmental conditions did considerable damage. PEMEX implemented a rapid repair program and was able to bring tile production back to its normal levels within two months. Subsequently, PEMEX, jointly with Instituto Mexicano del Petro´leo (IMP), launched an extensive program to inspect, assess, and repair the facilities. Results of the initial assessments indicated that the assessment parameters, as well as the metocean criteria utilized, were not suitable for Bay of Campeche. A detailed risk study considering the site-specific conditions and requirements was performed. Utilizing probability-based risk assessment techniques, a new criteria, known as the “transitory criteria,” was developed. The transitory criteria was then used to reassess the platforms and pipelines in the southwest marine region of BOC. Critically damaged platforms were identified for repair. The scope of repairs included jacket structural members and support framing for deck facilities. An overview of various techniques used for repairs of the underwater jacket structural members and joints is given. Different underwater repair methods are discussed. Repairs of both jacket and deck damages caused by hurricane Roxanne are presented as examples. The repair methods used are based on currently available technology and they will provide practical examples for economical platform repair in shallow, warm water environments. [S0892-7219(00)01101-8]
Characterization of 1,1-Dihydroperfluorooctyl Methacrylate (PFOMA) by XPS
Authors: Kassis Camille M. , Steehler Jack K. , Linton Richard W.
Published: July 2002

A sample of 1,1-dihydroperfluorooctyl methacrylate (PFOMA), a low surface energy polymeric material prepared by homogeneous free radical solution polymerization in supercritical CO2, has been investigated by x-ray photoelectron spectroscopy (XPS) using a Perkin-Elmer Physical Electronics Model 5400 spectrometer with monochromatic Al Kα x rays. Knowledge of the surface composition of PFOMA is significant since potential applications of this homopolymer include use in polymer blends where this material would be expected to be the surface active species. Controlled surface studies were conducted on a thick polymer film (∼0.5 μm) spun cast from solution onto silicon. Although the F 1s and O 1s regions were structurally straightforward to interpret, the C 1s window showed the expected pattern of functional group components.
Fe Chalcogenides by X-ray Photoemission Spectroscopy
Authors: Shimada Kenya , Mizokawa Takashi , Mamiya Kazutoshi , Saitoh Tomohiko , Fujimori Atsushi , Kamimura Takashi
Published: July 2002

In this article, x-ray photoelectron spectroscopy (XPS) spectra of iron chalcogenides, FeS, Fe7S8, and Fe7Se8 are presented. FeS (troilite) and Fe7S8 (pyrrhotite) are among the most common iron compounds on earth. FeS is antiferromagnetic below the Néel temperature of TN=593–598 K. Above Tα=420 K, FeS is a metal with an NiAs-type crystal structure, but becomes an insulator with a narrow band gap of 0.04 eV below Tα. This transition known as the α-transition is accompanied by a small displacement of the Fe and S atoms from the regular NiAs-type structure. Fe7S8 and Fe7Se8 are ferrimagnetic metals with Néel temperatures of TN=578 and 423–460 K, respectively. The crystal structures of Fe7S8 and Fe7Se8 are derived from the NiAs-type one by introducing ordered Fe vacancies. The polycrystalline samples were synthesized by the Bridgman method. Clean surfaces were obtained by scraping in situ with a diamond file. All the XPS spectra of the iron chalcogenides are taken at room temperature.
Electron-beam fabrication of nonplanar templates for contact printing
Authors: Rhee K. W. , Shirey L. M. , Isaacson P. I. , Kornegay C. F. , Dressick W. J. , Chen M.-S. , Brandow S. L.
Published: July 2002

Templates for contact printing applications have been fabricated on convex and concave surfaces using electron-beam lithography. Curved quartz lens blanks, coated with a chrome layer to suppress charging, were spincoated with a layer of polymethylmethacrylate (PMMA). Features were patterned into the PMMA followed by development, pattern transfer into the chrome by wet etch, and reactive-ion etching (RIE) of the chrome masked quartz. Features to 0.3 μm have been patterned and transferred ∼600 nm into the underlying quartz substrate by RIE, with less than a 10% etch depth variation across the sample. The patterned substrate was then used as a template to cast polymer stamps from poly(dimethylsiloxane). This approach provides a convenient method of fabricating curved templates for contact printing.
Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges
Authors: Woodworth J. R. , Riley M. E. , Amatucci V. A. , Hamilton T. W. , Aragon B. P.
Published: July 2002

In this article, we report the absolute intensities of ultraviolet light between 4.9 and 24 eV (250 to 50 nm) striking a silicon wafer in a number of oxide etch processing discharges. Our emphasis is on photons with energies greater than 8.8 eV, which have enough energy to damage SiO2. These discharges were in an inductively driven Gaseous Electronics Conference (GEC) reference cell which had been modified to more closely resemble commercial etching tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the vacuum ultraviolet (VUV) light in these discharges is strongly trapped. For the pure halocarbon gases examined in these experiments (C2F6, CHF3, C4F8), the fluxes of VUV photons to the wafer varied from 1 to 3×1015 photons/cm2 s or equivalently from 1.5 to 5 mW/cm2. These measurements imply that 0.1%–0.3% of the rf source power to these discharges ends up hitting the wafer as VUV photons for our typical 20 mT, 200 W rf discharges. For typical “ashing” discharges containing pure oxygen, the VUV intensities are slightly higher—about 8 mW/cm2. As argon or hydrogen diluents are added to the fluorocarbon gases, the VUV intensities increase dramatically, with a 10/10/10 mixture of Ar/C2F6/H2 yielding VUV fluxes on the wafer 26 mW/cm2 and pure argon discharges yielding 52 mW/cm2. Adding a rf bias to the wafer had only a small effect on the VUV observed through a side port of the GEC cell.
Released submicrometer Si microstructures formed by one-step dry etching
Authors: Tian W.-C. , Pang S. W.
Published: July 2002

Microstructures with submicrometer gaps in Si were fabricated by etching with Cl2 and F-based gases in inductively coupled plasma systems. Released cantilevered beams with a 0.1 μm gaps and 4 μm thick were fabricated using Cl2 etching. Etching in Cl2 provides vertical profile and smooth morphology for submicrometer trenches. It has been applied to form a clamped–clamped beam resonator with 0.2 μm gaps between the resonating beam and electrodes. For trenches with 0.1 μm openings, the F-based etching resulted in tapered etch profile and the top of the trenches was eventually closed due to polymer deposition. Based on faster lateral etch rate for n++ Si in Cl2 etching, a one step dry etching process was used to pattern and release microstructures from the substrate. Residues on the surface after F-based etching can be removed by overetching and the charging effect can be avoided by etching in Cl2.
Chemically enhanced focused ion beam micromachining of copper
Authors: Gonzalez J. C. , Griffis D. P. , Miau T. T. , Russell P. E.
Published: July 2002

Chemically enhanced focused ion beam micromachining of thin film Cu on Si substrates has been investigated. Barrier layers and dielectric layers were considered as well. The gases investigated include the Cl containing examples of C2Cl4, C2H4Cl2, and CHCl2CCl3 as well as the oxygen containing gases ethanol, and methanol and water vapor. Crystallographic channeling effect results in nonuniform Cu milling, insufficient selectivity and poor end-point detection. However, the gases investigated were shown to enhance the milling homogeneity, improve the end-point detection, and provide higher selectivity. A Cu/SiO2 selectivity of greater than 4 was obtained when using ethanol as the etching gas.
Quantitative analysis of nitrogen in oxynitrides on silicon by MCs+ secondary ion mass spectrometry?
Authors: Kataoka Y. , Shigeno M. , Wittmaack K.
Published: July 2002

The use of MCs+ secondary ion mass spectrometry for quantitative analysis of nitrogen in oxynitride layers on silicon was studied using Cs+ primary ions at energies between 250 eV and 1 keV and impact angles between 0° (normal incidence) and 80°. To achieve constant signal levels in the SiO2 layer, the oxide was chosen to be comparatively thick (4.9 nm). Due to differences in cesium surface coverage, the yields of the reference species Cs+ and SiCs+ varied with depth by up to three orders of magnitude, depending on the beam energy and the angle of incidence. Large differences in ion formation probability by up to a factor of 10 became evident from angular dependent changes of the OCs+/SiCs+ signal ratio in the oxide. Based on the observation that the depth dependent variations of the Cs+ and the SiCs+ signals are quite similar, attempts were made to rationalize the SiCs+ and OCs+ yields by normalizing to the Cs+ yields and the apparent target current. By way of scaling the NCs+ signals to the normalized OCs+ level in SiO2, the angular dependent variations of the apparent nitrogen content could be reduced to about 30%–40%. The remaining uncertainty is attributed to differences in the matrix effect for OCs+ and NCs+ in oxynitrides. It is also shown that silicon bombardment with cesium above “critical” angles of about 50° at 250 eV, 58° at 500 eV, and 65° at 1 keV causes very rapid ripple formation. This surface roughening is responsible for long-term changes of the SiCs+ matrix reference signal observed here and in earlier work.
pH-mediated frictional forces at tungsten surfaces in aqueous environments
Authors: Lim Min Soo , Perry Scott S. , Galloway Heather C. , Koeck Deborah C.
Published: July 2002

We have used atomic-force microscopy to measure the change in interfacial friction and adhesion between a tungsten surface and bare or alumina-coated Si3N4 tips. These measurements have been made in aqueous solutions ranging in pH from 2.2 to 8.2 in the absence of chemical or mechanical dissolution of the surface oxide. Friction is observed to vary with solution pH, and the specific manner in which interfacial friction depends on pH is influenced by the composition of the interface. The maximum friction force of the tungsten/silicon nitride system occurs at a pH of 4.7. The tungsten/alumina system has a maximum in the frictional force at a pH of 6.6. Frictional variations in these systems are related to pH-mediated changes in the electrostatic interaction between the probe tip and the sample. The pH dependence of the electrostatic interaction is determined by the relative isoelectric points of the contacting surfaces. These nanometer-scale measurements demonstrate a fundamental pathway by which variations in the frictional properties of an interface are introduced by properties of the surrounding liquid environment.
Stability of irradiation-induced point defects on walls of carbon nanotubes
Authors: Krasheninnikov A. V. , Nordlund K.
Published: July 2002

Using empirical-potential and tight-binding models, we study the structure and stability of atomic-scale irradiation-induced defects on walls of carbon nanotubes. Since atomic vacancies are the most prolific but metastable defects which appear under low-dose, low-temperature ion irradiation, we model the temporal evolution of single vacancies and vacancy-related defects (which isolated vacancies can turn into) and calculate their lifetimes at various temperatures. We further simulate scanning-tunneling microscopy (STM) images of irradiated nanotubes with the defects, employing for this the tight-binding Green’s function technique. Our simulations demonstrate that the defects live long enough at low temperatures to be detected by STM and that different defects manifest themselves in STM images in different ways, all of which makes it possible to detect and distinguish the defects experimentally.
Theory of nanotip formation
Authors: Bilbro Griff L.
Published: July 2002

We derive an analytic expression for the shape of nanometer-scale protrusions or nanotips which can form near the apex of a micrometer-scale Spindt-type base tip. We reconsider the model system that produces Taylor cones (that is, surface tension and Maxwell stress at a conductive meniscus), but here we admit only finite-diameter protrusions from a smooth surface. We find that the height of the resulting structures depends on absolute anode voltage as well as on the local electric field. We use the theory to predict the mechanical response of the field-emitting region of a Spindt microtip and to explain the empirical power-law relation between breakdown voltage and gap spacing in planar broad-area high-voltage gaps.
Inverse electronic scattering from shifted projections within the Fresnel-Kirchhoff formalism
Authors: Mayer A.
Published: July 2002

The inverse scattering technique we presented previously to achieve a sample reconstruction from the diffraction patterns obtained by electronic projection microscopy is extended to cope with the problem of automatically finding the characteristics of the incident wave (i.e., its amplitude and the source-sample distance). The underlying formalism is that of Fresnel-Kirchhoff, which describes the sample as a two-dimensional mask. By processing simultaneously the projections associated with a given sample translation, the accuracy of the reconstruction is improved and the evaluation of the source-sample distance is more efficient. The technique is applied to the analysis of a two-dimensional nanometric sample that is observed in Fresnel conditions with an electron energy of 40 eV. The parameters of the incident state are recovered precisely and reconstructions with a mean relative error around 1% are achieved.