bluuebunny/crossref_metadata_2025 huggingface dataset:
Spring Mixing: Turbulence and Internal Waves during Restratification on the New England Shelf
Authors: MacKinnon J. A. , Gregg M. C.
Published: January 2006

Integrated observations are presented of water property evolution and turbulent microstructure during the spring restratification period of April and May 1997 on the New England continental shelf. Turbulence is shown to be related to surface mixed layer entrainment and shear from low-mode near-inertial internal waves. The largest turbulent diapycnal diffusivity and associated buoyancy fluxes were found at the bottom of an actively entraining and highly variable wind-driven surface mixed layer. Away from surface and bottom boundary layers, turbulence was systematically correlated with internal wave shear, though the nature of that relationship underwent a regime shift as the stratification strengthened. During the first week, while stratification was weak, the largest turbulent dissipation away from boundaries was coincident with shear from mode-1 near-inertial waves generated by passing storms. Wave-induced Richardson numbers well below 0.25 and density overturning scales of several meters were observed. Turbulent dissipation rates in the region of peak shear were consistent in magnitude with several dimensional scalings. The associated average diapycnal diffusivity exceeded 10−3 m2 s−1. As stratification tripled, Richardson numbers from low-mode internal waves were no longer critical, though turbulence was still consistently elevated in patches of wave shear. Kinematically, dissipation during this period was consistent with the turbulence parameterization proposed by MacKinnon and Gregg, based on a reinterpretation of wave–wave interaction theory. The observed growth of temperature gradients was, in turn, consistent with a simple one-dimensional model that vertically distributed surface heat fluxes commensurate with calculated turbulent diffusivities.
Near-Inertial Waves on the New England Shelf: The Role of Evolving Stratification, Turbulent Dissipation, and Bottom Drag
Authors: MacKinnon J. A. , Gregg M. C.
Published: January 2006

Energetic variable near-inertial internal waves were observed on the springtime New England shelf as part of the Coastal Mixing and Optics (CMO) project. Surface warming and freshwater advection tripled the average stratification during a 3-week observational period in April/May 1997. The wave field was dominated by near-inertial internal waves generated by passing storms. Wave evolution was controlled by a balance among wind stress, bottom drag, and turbulent dissipation. As the stratification evolved, the vertical structure of these near-inertial waves switched from mode 1 to mode 2 with associated changes in the magnitude and location of wave shear. The growth of mode-2 waves was attributable to a combination of changing wind stress forcing and a nonlinear coupling between the first and second vertical modes through quadratic bottom stress. To explore both forcing mechanisms, an open-ocean mixed layer model is adapted to the continental shelf. In this model, surface wind stress and bottom stress are distributed over the surface and bottom mixed layers and then projected onto orthogonal vertical modes. The model replicates the correct magnitude and evolving modal distribution of the internal waves and confirms that bottom stress can act to transfer energy between internal wave modes.
Driving Forces of Interleaving in the Baroclinic Front at the Equator
Authors: Kuzmina Natalia , Lee Jae Hak
Published: January 2006

The different types of instability in the equatorial β-plane approximation are analyzed by means of a 2D linear stability problem. The double-diffusive (DD) and diffusive/baroclinic (2D baroclinic and McIntyre) instabilities are shown not to develop if contours of the mean salinity/density have a parabolic, symmetrical-relative-to-the-equator shape. Using modeling results, an illustrative scheme of Equatorial Undercurrent (EUC) regions where different types of instability can develop is presented and subsequently applied to understand the driving forces of the intrusions observed in a closed spaced CTD section, located between the equator and 1°N. Long coherence intrusions are situated within two isopycnal layers, aligned to 25 (layer 1) and 26.3 (layer 2) σT, where the vertical shear is low. It was shown from the model that the layer-1 intrusions being observed in the midlayer of the EUC where the mean horizontal gradient of salinity is approximately constant are likely generated by a combined effect of DD instability and instability due to linear horizontal shear. The layer-2 intrusions being observed in the lower part of EUC where the mean salinity contours have a parabolic shape likely arise because of linear horizontal shear only, while double diffusion can be considered as an effect that increases the growth rate of unstable modes. Special attention is focused on two different parts of the EUC in the mixing of the thermocline. It is noted that the EUC only makes the mass transfer by long coherence intrusions in certain layers where the vertical shear is small. Conversely, the EUC contributes to the growth rate of unstable modes due to the horizontal linear shear.
Wind-Induced Circulation in Semienclosed Homogeneous, Rotating Basins
Authors: Sanay Rosario , Valle-Levinson Arnoldo
Published: January 2006

The wind-induced circulation over laterally varying bathymetry was investigated in homogeneous systems using the three-dimensional Regional Ocean Model System (ROMS). The investigation focused on the influence of the earth’s rotation on the lateral distribution of the flow, with particular emphasis on the transverse circulation. Along-basin wind stress with no rotation caused a circulation dominated by an axially symmetric transverse structure consisting of downwind flow over the shoals and upwind flow in the channel along the whole domain. Transverse circulation was important only at the head of the system where the water sank and reversed direction to move toward the mouth. The wind-induced flow pattern under the effects of the earth’s rotation depended on the ratio of the maximum basin’s depth h to the Ekman depth d. The solution tended to that described in a nonrotating system as h/d remained equal to or below 1. For higher values of h/d, the longitudinal flow was axially asymmetric. Maximum downwind flow was located over the right shoal (in the Northern Hemisphere, looking downwind). The transverse component of velocity described three gyres. The main gyre was clockwise (looking downwind) and occupied the entire basin cross section, as expected from the earth’s rotation and the presence of channel walls. The other two gyres were small and localized and were linked to the lateral distribution of the along-channel velocity component, which in turn was dictated by bathymetry. These results compared favorably with a limited set of observations and are expected to motivate future measurements.
Boundary Intensification of Vertical Velocity in a β-Plane Basin
Authors: Pedlosky Joseph , Spall Michael A.
Published: January 2006

The buoyancy-driven circulation of simple two-layer models on the β plane is studied in order to examine the role of beta in determining the magnitude and structure of the vertical motions forced in response to surface heating and cooling. Both analytical and numerical approaches are used to describe the change in circulation pattern and strength as a consequence of the planetary vorticity gradient. The physics is quasigeostrophic at lowest order but is sensitive to small nonquasigeostrophic mass fluxes across the boundary of the basin. The height of the interface between the two layers serves as an analog of temperature, and the vertical velocity at the interface consists of a cross-isopycnal velocity, modeled in terms of a relaxation to a prescribed interface height, as well as an adiabatic representation of eddy thickness fluxes parameterized as lateral diffusion of interface displacement. In the numerical model the lateral eddy diffusion of heat is explicitly represented by a resolved eddy field. In the plausibly more realistic case, when the lateral diffusion of buoyancy dominates the diffusion of momentum, the major vertical velocities occur at the boundary of the basin as in earlier f-plane studies. The effect of the planetary vorticity gradient is to intensify the sinking at the western wall and to enhance the magnitude of that sinking with respect to the f-plane models. The vertical mass flux in the Sverdrup interior exactly balances the vertical flux in the region of the strong horizontal transport of the western boundary current, leaving the net flux to occur in a very narrow region near the western boundary tucked well within the western boundary current. On the other hand, if the lateral diffusion of heat is arbitrarily and unrealistically eliminated, the vertical mass flux is forced to occur in the interior. The circulation pattern is extremely sensitive to small net inflows or outflows across the basin perimeter. The cross-basin flux determines the interface height on the basin’s eastern boundary and affects the circulation pattern across the entire basin.
Eulerian and Lagrangian Velocity Distributions in the North Atlantic
Authors: LaCasce J. H.
Published: January 2006

Velocity probability density functions (PDFs) are calculated using data from subsurface current meters in the western North Atlantic Ocean. The PDFs are weakly, but significantly, non-Gaussian. They deviate from normality because of an excess of energetic events, and there are evidently more such events in the main thermocline than in the deep ocean. The PDFs are also compared with those obtained from subsurface floats in the same region. The PDFs are statistically indistinguishable so long as the float data are averaged in appropriately sized bins. Taking too-small bins yields overly Gaussian float PDFs, and taking too-large bins yields too-non-Gaussian PDFs. With this caveat, the Lagrangian and Eulerian PDFs agree, consistent with expectations from theory and previous numerical simulations.
Geostrophic Adjustment of an Isolated Diapycnal Mixing Event and Its Implications for Small-Scale Lateral Dispersion
Authors: Lelong M-Pascale , Sundermeyer Miles A.
Published: January 2006

In this first of two companion papers, the time-dependent relaxation of an isolated diapycnal mixing event is examined in detail by means of numerical simulations, with an emphasis on the energy budget, particle displacements, and their implications for submesoscale oceanic lateral dispersion. The adjustment and dispersion characteristics are examined as a function of the lateral extent of the event L relative to the Rossby radius of deformation R. The strongest circulations and horizontal displacements occur in the regime R/L ≈ O(1). For short times, less than an inertial period, horizontal displacements are radial. Once the adjustment is completed, displacements become primarily azimuthal and continue to stir fluid over several to tens of inertial periods. The cumulative effect of many such events in terms of the effective lateral dispersion that they induce is examined in the companion paper.
Ballooning of River-Plume Bulge and Its Stabilization by Tidal Currents
Authors: Isobe Atsuhiko
Published: January 2006

When freshwater debouches into an adjacent ocean, an anticyclonic eddy (bulge) is formed in front of the river mouth. It is well known that a bulge growing offshore (ballooning) hardly reaches a steady state in the absence of either ambient currents or wind forcing. This study provides a physical interpretation for the ballooning of river-plume bulges by conducting numerical experiments in which a river plume is induced by a coastal freshwater source. Part of the freshwater released to the model ocean undergoes inertial instability. Near-inertial oscillations are predominant when disturbances are not forced in ambient waters of the river plume. These isotropic disturbances are amplified by inertial instability, so that unstabilized freshwater can move in arbitrary directions. Thus, unstabilized freshwater does not need to move toward the coastal boundary current on the right-hand side of the river mouth. Freshwater unstabilized for a long time can stay in the bulge for a long time. Unstabilized freshwater accumulates gradually in the bulge, and so ballooning occurs. When the direction of disturbances is prescribed in ambient waters, unstabilized freshwater is forced to move in the same direction. Thereby, the motion of unstabilized freshwater is restricted in the alongshore direction when background disturbances are induced by alongshore tidal currents. It is therefore concluded that tidal currents play a role in stabilizing the offshore growth of river-plume bulges in coastal and shelf waters.
Reliability of Total Test Scores When Considered as Ordinal Measurements
Authors: Biswas Ajoy Kumar
Published: January 2006

This article studies the ordinal reliability of (total) test scores. This study is based on a classical-type linear model of observed score (X), true score (T), and random error (E). Based on the idea of Kendall's tau-a coefficient, a measure of ordinal reliability for small-examinee populations is developed. This measure is extended to large (theoretically, infinite) examinee populations. This extended measure is identified as the population version of Kendall's tau-a. Appropriateness of the traditional product moment correlation-based measures,. TX and .XX0, is reviewed. It is observed that. TX and .XX0 are appropriate within the family of normal distributions of (T, E) but are inappropriate in the family of nonnormal distributions. A simulated data example is considered to show that the traditional product moment correlation-based measures may be misleading. Furthermore, practical procedures are suggested for estimating ordinal reliability. Real test score data are used for demonstration. Index terms: ordinal measures, linear model in classical test theory, test score reliability, Kendall's tau-a
Correcting Coefficient Alpha for Correlated Errors: Is αK a Lower Bound to Reliability?
Authors: Rae Gordon
Published: January 2006

When errors of measurement are positively correlated, coefficient alpha may overestimate the “true” reliability of a composite. To reduce this inflation bias, Komaroff (1997) has proposed an adjusted alpha coefficient, ak. This article shows that ak is only guaranteed to be a lower bound to reliability if the latter does not include correlated error. If one's definition of reliability includes correlated error, then an alternative adjusted alpha, ar, is suggested, which will always be a lower bound. Index terms: coefficient alpha, adjusted alpha, correlated errors, lower bound, reliability
Lessons From a Juvenile Training School
Authors: Inderbitzin Michelle
Published: January 2006

This article examines the lessons learned by youths confined to a maximum-security juvenile correctional facility. Using data from an ethnographic study of a cottage of violent offenders in one state’s end-of-the-line training school, the author describes the lessons the institution and its staff members hoped to teach the young people in their care and the informal but vital lessons the inmates indicated they had learned during their incarceration. The continued viability of training schools as a response to serious and violent juvenile offenders is analyzed and discussed.
Examining the Symptoms of Groupthink and Retrospective Sensemaking
Authors: Henningsen David Dryden , Henningsen Mary Lynn Miller , Eden Jennifer , Cruz Michael G.
Published: January 2006

The symptoms of groupthink traditionally have been treated as part of a single process associated with poor decision making in groups. The present study explores the symptoms of groupthink as reflecting two distinct processes that vary depending on the confidence individuals have in the decision favored by the group. It is further argued that past research using qualitative approaches may produce an illusory correlation among the groupthink symptoms because of retrospective sensemaking occurring when individuals have evidence they have made a poor decision. An experiment, providing support for each of these contentions, is performed.
Measuring Group Efficacy in Virtual Teams
Authors: Hardin Andrew M. , Fuller Mark A. , Valacich Joseph S.
Published: January 2006

Group efficacy has received renewed attention in the group literature. Although the relationship between group efficacy and group performance is well established, debate continues on how best to measure the construct. Although most research has explored this issue using collocated groups, this article examines the measurement of group efficacy in virtual teams and explores why some measurement methods may be more appropriate for use in noncollocated groups. Fifty-three senior-level university students involved in virtual team projects were administered questionnaires over the course of their project. As theorized, data analyses revealed that group efficacy beliefs reached by consensus were significantly higher than those measured by surveys administered to individual virtual team members. In addition, support for the greater predictability of an aggregated method over a group consensus method was demonstrated. Follow-up analyses show that group outcome perceptions were significantly related to team performance. Implications and future research are discussed.
Where the Action Is
Authors: Harrington Brooke , Fine Gary Alan
Published: January 2006

Although small group research has been marginalized within sociology during the past decades, the authors argue that a focus on interaction arenas can contribute to a more complete analysis of social life. Specifically, the authors examine three central domains of sociological analysis—culture, organizations, and the economy—to demonstrate how a focus on the mesolevel of analysis allows for a merging of macrosociology and microsociology. The authors draw on the perspective of sociological miniaturism to provide a model for cross-level research.
Using Graduated in Vivo Exposure to Treat a Claustrophobic Response to Nasal Continuous Positive Airway Pressure
Authors: McCrae Christina S. , Ingmundson Paul T.
Published: January 2006

Continuous positive airway pressure (CPAP) is the preferred treatment for obstructive sleep apnea syndrome because it safely and effectively reduces or eliminates nighttime upper airway obstruction. Unfortunately, CPAP adherence rates are low(30% to 40%). For some patients, a history of trauma contributes to nonadherence by triggering a claustrophobic response to CPAP. Exposure is the treatment of choice for anxiety-based responses, such as claustrophobia. Here, we provide the first demonstration of the successful use of graduated in vivo exposure to treat an individual experiencing a trauma-related claustrophobic response to CPAP.
Influence of steel strength and loading mode on fatigue properties of resistance spot welded H section specimen
Authors: Fourlaris G. , Hambling S. J. , Jones T. B.
Published: January 2006

The drive to reduce vehicle mass by substituting mild steel with thinner high strength steel means that design engineers are now working closer to the design limits with respect to the fatigue performance of spot welded structures. Consequently, the present study was initiated to evaluate the factors that influence the fatigue performance of spot welded H sections so as to optimise the performance of spot welded high strength steel structures. The results obtained indicated that steel strength had little effect on fatigue performance while, in contrast, the loading mode, weld size and sheet thickness had a significant influence on it. The results of shear loading were up to 10 times greater compared with that under peel loading conditions. Under shear loading conditions full plug failures were noted, whereas with peel loaded variants partial plug failures predominated. With respect to enhancing the fatigue properties the use of larger weld sizes was shown to be beneficial.
Temperature and strain rate dependence of the dynamic strain aging effect in an Al–Zn–Mg alloy
Authors: Hörnqvist M. , Karlsson B.
Published: January 2006

An AA7030 alloy (Al–5·4Zn–1·2Mg) was tested for evidence of dynamic strain aging in naturally aged and peak aged condition and under varying conditions in terms of strain rate and temperature. Clear evidence in terms of strain rate sensitivity, serrated yielding (Portevin–Le Chatelier effect) and propagative plastic instabilities was observed in the naturally aged temper while the peak aged temper only showed serrated yielding. Further evidence of dynamic strain aging was the temperature and strain dependence of the strain rate sensitivity, which can be explained by the additional dislocation activation energy resulting from solute pinning. Investigation of the specimen surfaces was carried out to reveal an orange peel structure with pronounced glide bands. Small cracks within individual grains rather than grain boundary cracking could be observed.
Fatigue crack susceptibility of electrical discharge drilled holes in nickel based heat resistant alloy
Authors: Kang S. H. , Kim D. E.
Published: January 2006

Electrical discharge (ED) drilling is one of the prevalent processes that is utilised to drill deep holes in hard to machine materials such as nickel based heat resistant alloys used for turbine applications. In order to satisfy the high durability needs of heavy duty engines applicable to power generation industry, cooling design for hot gas path components has become complicated. ED drilling technique has been employed frequently to machine holes in complex parts. Thus, the effects of ED drilling and post electrical discharge machining (EDM) processes on the fatigue durability of the materials need to be clearly understood. However, the characteristics of the altered material zone (AMZ) created by ED drilling has not been fully analysed in terms of fatigue crack susceptibility. In order to investigate the effects of ED drilling process, fatigue test specimens with ED drilled through holes machined under four EDM conditions were fabricated. For some of the specimens, subsequent heat treatment was performed in order to verify the effect of the AMZ. Also two configurations of the hole modifications were attempted to assess whether getting rid of the AMZ from the weakest spot of the hole edge was effective to extend the fatigue durability. After the fatigue test, crack behaviour of the ED drilled inside hole was analysed using scanning electron microscope (SEM) fractography. Based on the findings of the present study, desirable ED drilling parameters in association with the post treatment processes are suggested.
Influence of pin geometry on material flow in friction stir welding process
Authors: Zhao Y.-H. , Lin S.-B. , Qu F.-X. , Wu L.
Published: January 2006

The material flow in friction stir welded 2014 Al alloy has been investigated using a marker insert technique (MIT). Results of the flow visualisation show that the material flow is asymmetrical during the friction stir welding (FSW) process and there are also significant differences in the flow patterns observed on advancing and retreating sides. Combining the data from all the markers, a three-dimensional (3D) flow visualisation similar to the 3D image reconstruction technique was obtained. The 3D plot gives the tendency chart of material flow in FSW process and from the plot it can be seen that there is a vertical and circular motion around the longitudinal axis of the weld. The influence of the pin geometry on material flow in FSW was studied. When the column and taper pin are used, there is a ‘hole’ defect in the vertical mixing plot. When the taper with screw thread pin is used, the vertical material flow is more obvious and there is no distinct ‘hole’. Viewing from the advancing side, the pin geometry will affect the position where minimal transport distance against the welding direction occurs.
Numerical prediction for columnar to equiaxed transition in solidified Ti–Al intermetallic alloy ingots by stochastic model
Authors: Liu D. R. , Guo J. J. , Wu S. P. , Su Y. Q. , Fu H. Z.
Published: January 2006

A stochastic model of macro- and microtype for predicting the columnar–equiaxed transition (CET) during solidification processes of Ti–Al intermetallic alloy ingots is developed in the present paper. The macroscopic part is based on a finite difference method (FDM) for modelling of heat transfer. The microscopic part consists of a cellular automaton method (CA) for modelling of nucleation and growth. The formation of a shrinkage cavity at the top of ingot is taken into account. The effects of casting variables on CET are presented and discussed. A quantitative relation between CET position and casting variables is obtained. The columnar zone is found to expand with decreasing alloy composition, mould preheated temperature and convection, and increasing thermal conductivity of mould, superheat and heat transfer coefficient at mould/metal interface. And the highly influential variables are superheat, heat transfer coefficient and convection.
Synthesis and evaluation of hardness and sliding wear resistance of electrodeposited nanocrystalline Ni–Fe–W alloys
Authors: Sriraman K. R. , Sundara Raman S. Ganesh , Seshadri S. K.
Published: January 2006

The present work involves synthesis, characterisation and evaluation of hardness and sliding wear resistance of electrodeposited nanocrystalline Ni–Fe–W alloys. The crystallite size reduced with an increase in current density owing to an increase in the amount of alloying elements (Fe and W). Ni–Fe–W alloy with 23 at.-%Fe and 1·3 at.-%W plated at 0·1 A cm−2exhibited the maximum hardness of 563 HV. The alloys exhibited a direct Hall–Petch relation above a crystallite size of 12 nm and an inverse Hall–Petch relation below 12 nm. The wear resistance of the alloys increased with a reduction in the crystallite size in the direct Hall–Petch region and decreased in the inverse Hall–Petch region. Ni–Fe–W coatings with 23 at.-%Fe and 1·3 at.-%W plated at 0·1 A cm−2exhibited superior wear resistance.
Friction layers produced in two steels during laboratory friction testing
Authors: Liu C. , Zhao Z. , Liu Y. , Bhole S. D.
Published: January 2006

The friction layers produced on SAE type 1065 and 20Mn2WNbB steels during laboratory friction testing have been characterised using optical microscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. A white layer is formed on the surface of SAE 1065 steel, composed of abnormal quenched martensite with a microhardness of 1020 HV(100 g). A dark grey friction layer with a microhardness of 600 HV(100 g) is formed on the surface of 20Mn2WNbB steel. This layer consists of tempered lath martensite with a low carbon content. Formation of the white layer in SAE 1065 steel occurs through austenitisation of the steel surface due to friction at a high sliding rate, followed by rapid cooling to a martensite structure. The martensite structure in this white layer exhibits a finer grain size and higher dislocation density than that obtained by normal quenching. However, in 20Mn2WNbB steel, the quenched martensite structure is transformed into tempered martensite by self-tempering during cooling. Charpy impact tests show that the impact toughness of SAE 1065 steel is significantly decreased owing to the presence of the white layer. However, there is only a small effect of the friction layer on the impact toughness of 20Mn2WNbB steel.
In situ surface displacement analysis of fracture and fatigue behaviour under bending conditions of sandwich beam consisting of aluminium foam core and metallic face sheets
Authors: Sha J. B. , Yip T. H. , Wong S. K. M.
Published: January 2006

The present paper deals with the study of the mechanical behaviour of sandwich beams under monolithic and cyclic bending. The strains and displacements were monitored by in situ surface displacement analysis (SDA) software. The sandwich beams consisted of an aluminium foam core covered by metallic face sheets. For a certain sandwich geometrical configuration, the operative failure mode is the same under both monolithic and cyclic bending conditions. Indentation (ID) and core shear (CS) are the basic failure modes, which depend entirely on the geometry of the sandwich beam. The SDA results show that ID is localised compression of the beam adjacent to the inner rollers, where the displacement and strain are at a maximum. As for the CS failure mode, failure happens within the core between the inner and outer rollers, where shear crack initiation and growth correspond to the maximum shear strain, accompanied by discontinuous displacements in both vertical and horizontal directions. Owing to constraint of the weak foam core imposed by the strong metallic face sheets in a sandwich beam, the core can bear stresses higher than the yield strength of monolithic foam by a factor of 1·6–3·2 for both CS and ID failure modes. This factor depends mainly on the geometry of the sandwich beam. Similarly, the fatigue limit of the core in the sandwich beam is also higher than the fatigue strength of monolithic foam. The stronger is the constraint, the higher is the fatigue limit of the core. The fatigue limit of a sandwich beam also relates to the failure mode. At fatigue ratio R=0, the fatigue limit of sandwich beams failing by the ID mode is higher than that of beams which fail by the CS mode.
Extent of back diffusion during solidification of experimental nickel based single crystal superalloy
Authors: Thirumalai A. , Akhtar A. , Reed R. C.
Published: January 2006

The microsegregation inherited from the directional solidification and quenching (DSQ) of an experimental third generation single crystal superalloy is characterised using electron probe microanalysis (EPMA). A statistical treatment of the data is used to estimate the composition of the solid in the mushy zone. Comparison of the experimental data with the predictions from a numerical model indicates that the results cannot be rationalised without acknowledging that back diffusion is occurring; it is demonstrated that the magnitudes of the diffusion coefficients which need to be invoked are consistent with recent experimental measurements of the coefficients deduced from diffusion couples.
Effects of post-weld heat treatment on microstructure and mechanical properties of friction stir welded joints of 2219-O aluminium alloy
Authors: Feng J. C. , Chen Y. C. , Liu H. J.
Published: January 2006

Post-weld heat treatment (PWHT) of 2219-O aluminium alloy friction stir welding joints was carried out at solution temperatures of 480, 500 and 540°C for 32 min followed by aging at 130°C for 9 h. The effects of PWHT on the microstructure and mechanical properties of the joints were investigated. Experimental results show that PWHT causes coarsening of the grains in the weld, and the coarsening degree increases with increasing solution temperature. The tensile strength of the heat treated joints increases with increasing solution temperature. The maximum tensile strength can reach 260% that of the base material at the solution temperature of 540°C. PWHT has a significant effect on the fracture locations of the joints. When the solution temperature is lower than 500°C, the joints fracture in the base material; when the temperature is higher than 500°C, the joints fracture in the weld. The change of the fracture locations of joints is attributed to the presence of precipitate free zones beside the grain boundaries and coarsening equiaxed grain structures in the weld.
Formation mechanism of connected polycrystalline iron fibres by pyrolysis of iron carbonyl in magnetic field
Authors: Chu Z. Y. , Cheng H. F. , Zhou Y. J. , Tang G. P. , Cheng S. J. , Xie W.
Published: January 2006

Polycrystalline iron fibres (PIFs) can be prepared by pyrolysis of iron carbonyl in a magnetic field, but some of them usually combine. In the present work, the formation mechanism of connected PIFs has been studied by varying magnetic field intensity, feed volume and feed rate. The results reveal that the weight percentage of connected PIFs can be reduced by increasing the magnetic field intensity, increasing the feed rate and, especially, decreasing the feed volume. This is because the process is one of ‘space confined growth’, and only when the feed volume is reduced below a threshold can the concentration of connected fibres be markedly suppressed. In addition, this threshold increases with increasing magnetic field intensity, because this change preferentially aids the growth of original or new single fibres. The average diameter of single PIFs also decreases greatly with a reduction in percentage of connected fibres. An average diameter of 0·40 μm can be obtained with the amount of connected fibres reduced below 2·0 wt-%.
Thermodynamic and kinetic analysis of interfacial reaction between CBN and titanium activated Ag–Cu alloy
Authors: Ding W. F. , Xu J. H. , Shen M. , Fu Y. C. , Xiao B.
Published: January 2006

Thermodynamic and kinetic analysis was performed in order to study the interfacial reaction mechanism of cubic boron nitride (CBN) abrasive grains and Ti activated Ag–Cu filler alloy during high temperature brazing. Meanwhile, microstructure of the interfacial layer was experimentally detected using scanning electron microscope (SEM), energy dispersion spectrometer (EDS) and X-ray diffraction (XRD) in the present paper. The results indicate that according to the thermodynamic theory, the interfacial reaction has been proved feasible, and during brazing the special active element Ti concentrated to and reacted with the CBN abrasive to form TiB2 and TiN, which joined hard the abrasive grain and steel substrate. Furthermore, the diffusion activation energy of the growing process in the interfacial reaction layer has discovered that the layer growth largely depends on the new formed TiN under conditions of 1153–1193 K and 5–30 min.
Corrosion characteristics of aluminium based metal matrix composites
Authors: Gurrappa I. , Prasad V. V. Bhanu
Published: January 2006

There is a growing demand both in aerospace as well as commercial markets for lighter weight, higher stiffness and higher thermal stability materials to solve the design engineer's problems of reduced mass, higher access speeds, improved mechanical and thermal stability for today's advanced technologies. Metal matrix composites satisfy the above mentioned properties. However, corrosion is a major concern as the secondary phase formation in the matrix takes place as a result of ceramic particle addition, which threatens their exploitation for such applications. In the current paper, the corrosion characteristics of different aluminium based metal matrix composites of varying volume fractions of SiC (SiC/Al) has been studied systematically. Pitting corrosion studies have been investigated in detail. Scanning electron microscopy (SEM) has been used not only to understand the nature of corrosion but also to identify the location of corrosion in the matrix phase. X-ray diffraction analysis (XRD) has been used to determine the intermetallics formation. EPMA studies have been carried out to determine the distribution of SiC particulates in the matrix as well as the location of intermetallics. Finally, the corrosion mechanism causing the SiC/Al composites to degrade under marine environmental conditions has been presented and the necessity of finding suitable surface coatings to enhance the corrosion resistance of these composites is stressed.
Space charge limited conduction and determination of density of localised states in semiconductor cobalt doped TiO2
Authors: Okutan M. , Yakuphanoglu F. , Bakan H. I. , Inanir F.
Published: January 2006

The space charge limited conduction (SCLC) mechanism in Co doped TiO2 has been investigated at different temperatures. At lower electric fields, ohmic behaviour is observed while at higher electric fields nonohmic behaviour is observed. The results obtained confirm the presence of SCLC in Co doped TiO2. The electronic parameters such as the position of the Fermi level above the valence band edge EF, the density of states in valence band NV and effective mass of holes mh were found as 12·32 meV, 1·26 × 1015 m−3 and 1·33 × 10−7 me, respectively. The distribution of localised states in the forbidden band gap of the Co doped TiO2 was characterised by current–voltage measurements and the density of localised states near the Fermi level N(EF) was found to be 2·11 × 1017 eV−1 m−3.
Effect of mixed mode I/III loading on fracture toughness of 7010 aluminium alloy
Authors: Raju K. S. S. Eswar , Mukhopadhyay A. K. , Kamat S. V.
Published: January 2006

The effect of mixed mode I/III loading on the fracture toughness of 7010 aluminium alloy plate was investigated in the peak aged (T6) and overaged (T73) temper conditions. The fracture toughness of 7010 Al alloy was found to remain more or less unchanged with increasing mixed mode I/III loading for both aging tempers. The fracture, in both T6 and T73 tempers, occurred predominantly by a transgranular ductile mechanism of void nucleation, growth and coalescence under mode I as well as mixed mode I/III loading. Primary void formation at brittle intermetallic inclusions and their subsequent coalescence was determined to be the most important step in the fracture process. This coupled with the nature of the stress field ahead of the crack tip under mixed mode I/III loading was then used to explain the insignificant effect of mixed I/III loading on the fracture toughness in 7010 aluminium alloy.
Corrosion resistance of AA2219 aluminium alloy: Electrochemical polarisation and impedance study
Authors: Srinivasa Rao K. , Prasad Rao K.
Published: January 2006

The addition of copper increases the strength of aluminium, but decreases the localised corrosion resistance of the metal to seawater as the copper containing intermetallics exhibit different electrochemical properties from the matrix. The main requirement of corrosion resistance could be met through the surface modification by removing the copper rich phase. The present work involves investigations of the influence of prior copper removal treatment on the pitting and general corrosion resistance of AA2219 alloy containing a high copper content in different initial thermal tempers. Significant improvement in the pitting and general corrosion resistance after surface copper removal treatment was evident from the results of electrochemical polarisation and the impedance tests. Attempts were also was made to modify the surface further, with a conversion layer of cerium as an alternative to the chromate coating.
Residual stress magnitudes and related properties in quenched aluminium alloys
Authors: Tanner D. A. , Robinson J. S.
Published: January 2006

The surface and through thickness residual stress magnitudes present in heat treated high strength aluminium alloy components are frequently reported to exceed the uniaxial yield stress of small specimens of the same alloy measured immediately after quenching. In thick section plate and forgings, it is proposed that these high residual stress magnitudes are a consequence of hardening precipitation that occurs during quenching which allows a greater elastic stress to be supported. To investigate this theory, a Jominy end quench technique is used to determine the hardness of aluminium alloys 7010, 7175 and 5083 as a function of distance from the quenched end. Cooling curves have been measured for Jominy end quench specimens using deeply buried thermocouples and are compared with finite element model predictions. Tensile properties are also determined for small specimens quenched into cold and boiling water. Vickers hardness and X-ray diffraction residual stress measurements are undertaken on specimens of varying size acting as a comparison with the Jominy results. These results in combination with optical and electron microscopy data do suggest that low temperature rather than high temperature precipitation during the quench leads to increased as quenched mechanical strengths, with the consequence that less quench sensitive alloys will support higher residual stress magnitudes as section thicknesses increase.
The angiogenic function of nucleolin is mediated by vascular endothelial growth factor and nonmuscle myosin
Authors: Huang Yujie , Shi Hubing , Zhou Hao , Song Xiaomin , Yuan Shaopeng , Luo Yongzhang
Published: January 2006

Nucleolin, originally described as a nuclear protein, was recently found to be expressed on the surface of endothelial cells during angiogenic. However, the functions of cell-surface nucleolin in angiogenic remain mysterious. Here we report that upon endothelial cells adhering to extracellular matrix components, vascular endothelial growth factor (VEGF) mobilizes nucleolin from nucleus to cell surface. Functional blockage or down-regulation of the expression of cell-surface nucleolin in endothelial cells significantly inhibits the migration of endothelial cells and prevents capillary-tubule formation. Moreover, nonmuscle myosin heavy chain 9 (MyH9), an actin-based motor protein, is identified as a nucleolin-binding protein. Subsequent studies reveal that MyH9 serves as a physical linker between nucleolin and cytoskeleton, thus modulating the translocation of nucleolin. Knocking down endogenous MyH9, specifically inhibiting myosin activity, or overexpressing functional deficient MyH9 disrupts the organization of cell-surface nucleolin and inhibits its angiogenic function. These studies indicate that VEGF, extracellular matrix, and intracellular motor protein MyH9 are all essential for the novel function of nucleolin in angiogenic.
Intratumoral CD4+CD25+ regulatory T-cell-mediated suppression of infiltrating CD4+ T cells in B-cell non-Hodgkin lymphoma
Authors: Yang Zhi-Zhang , Novak Anne J. , Stenson Mary J. , Witzig Thomas E. , Ansell Stephen M.
Published: January 2006

Most non-Hodgkin lymphomas (NHLs) are of B-cell origin, but the tumor tissue can be variably infiltrated with T cells. In the present study, we have identified a subset of CD4+CD25+ T cells with high levels of CTLA-4 and Foxp3 (intratumoral Treg cells) that are overrepresented in biopsy specimens of B-cell NHL (median of 17% in lymphoma biopsies, 12% in inflammatory tonsil, and 6% in tumor-free lymph nodes; P = .001). We found that these CD4+CD25+ T cells suppressed the proliferation and cytokine (IFN-γ and IL-4) production of infiltrating CD4+CD25- T cells in response to PHA stimulation. PD-1 was found to be constitutively and exclusively expressed on a subset of infiltrating CD4+CD25- T cells, and B7-H1 could be induced on intratumoral CD4+CD25+ T cells in B-cell NHL. Anti-B7-H1 antibody or PD-1 fusion protein partly restored the proliferation of infiltrating CD4+CD25- T cells when cocultured with intratumoral Treg cells. Finally, we found that CCL22 secreted by lymphoma B cells is involved in the chemotaxis and migration of intratumoral Treg cells that express CCR4, but not CCR8. Taken together, our results suggest that Treg cells are highly represented in the area of B-cell NHL and that malignant B cells are involved in the recruitment of these cells into the area of lymphoma.
Acceleration of mesoderm development and expansion of hematopoietic progenitors in differentiating ES cells by the mouse Mix-like homeodomain transcription factor
Authors: Willey Stephen , Ayuso-Sacido Angel , Zhang Hailan , Fraser Stuart T. , Sahr Kenneth E. , Adlam Matthew J. , Kyba Michael , Daley George Q. , Keller Gordon , Baron Margaret H.
Published: January 2006

The cellular and molecular events underlying the formation and differentiation of mesoderm to derivatives such as blood are critical to our understanding of the development and function of many tissues and organ systems. How different mesodermal populations are set aside to form specific lineages is not well understood. Although previous genetic studies in the mouse embryo have pointed to a critical role for the homeobox gene Mix-like (mMix) in gastrulation, its function in mesoderm development remains unclear. Hematopoietic defects have been identified in differentiating embryonic stem cells in which mMix was genetically inactivated. Here we show that conditional induction of mMix in embryonic stem cell–derived embryoid bodies results in the early activation of mesodermal markers prior to expression of Brachyury/T and acceleration of the mesodermal developmental program. Strikingly, increased numbers of mesodermal, hemangioblastic, and hematopoietic progenitors form in response to premature activation of mMix. Differentiation to primitive (embryonic) and definitive (adult type) blood cells proceeds normally and without an apparent bias in the representation of different hematopoietic cell fates. Therefore, the mouse Mix gene functions early in the recruitment and/or expansion of mesodermal progenitors to the hemangioblastic and hematopoietic lineages.
Impact of anemia on hospitalization and mortality in older adults
Authors: Culleton Bruce F. , Manns Braden J. , Zhang Jianguo , Tonelli Marcello , Klarenbach Scott , Hemmelgarn Brenda R.
Published: January 2006

Although anemia is common in older adults, its prognostic significance is uncertain. A total of 17 030 community-dwelling subjects 66 years and older were identified between July 1 and December 31, 2001, and followed until December 31, 2004. Cox proportional hazards analyses were performed to determine the associations between anemia (defined as hemoglobin < 110 g/L) and hemoglobin and all-cause mortality, all-cause hospitalization, and cardiovascular-specific hospitalization. Overall, there were 1983 deaths and 7278 first hospitalizations. In patients with normal kidney function, adjusting for age, sex, diabetes mellitus, and comorbidity, anemia was associated with an increased risk for death (hazard ratio [HR], 4.29; 95% confidence interval [CI], 3.55-5.12), first all-cause hospitalization (HR, 2.16; 95% CI, 1.88-2.48), and first cardiovascular-specific hospitalization (HR, 2.49; 95% CI, 1.99-3.12). An inverse J-shaped relationship between hemoglobin and all-cause mortality was observed; the lowest risk for mortality occurred at hemoglobin values between 130 to 150 g/L for women and 140 to 170 g/L for men. Anemia is associated with an increased risk for hospitalization and death in community-dwelling older adults. Consideration should be given to redefine “normal” hemoglobin values in the elderly. Clinical trials are also necessary to determine whether anemia correction improves quality or quantity of life in this population.
Psychology in the Design of Multimedia Presentations in the Classroom: An Interview with Richard S. Velayo
Authors: Smith Paul C.
Published: January 2006

Paul Smith (PS), an Assistant Professor of Psychology at Alverno College (Milwaukee, W.) conducted this issue's interview for The Generalist's Corner. He chose multimedia instructional techniques as his focus and interviewed Richard Velayo (RV) as our expert. Velayo is an Assistant Professor at Pace University (New York, NY) and has made presentations on the topic of multimedia instruction at regional and national psychology conferences.
Collaborative Learning in an Introduction to Psychological Science Laboratory: Undergraduate Teaching Fellows Teach to Learn
Authors: Newcomb Andrew F. , Bagwell Catherine L.
Published: January 2006

In this article, we describe the laboratory component of an Introduction to Psychological Science course and a teaching fellows program in which undergraduates direct these laboratory experiences. We present the goals of the laboratory class and describe its curriculum, and we examine the goals and operations of the teaching fellows program. Furthermore, we consider the outcomes of this experience for introductory students and teaching fellows, and we examine the implications of the teaching fellows program for quality undergraduate education.