Extreme Boundary Research Articles

Suppression of chromium depletion and sensitization in austenitic stainless steel by surface mechanical attrition treatment

The effects of surface nanocrystallization via surface mechanical attrition treatment (SMAT) on degree of sensitization (DOS) of an austenitic stainless steel were investigated by means of double loop electrochemical potentiokinetic reactivation (DLEPR) test. The treated sample with grain size about 10nm showed very low degree of sensitization value which can be considered as the non-sensitized material. This is mainly due to the formation of twin boundaries in the microstructure of the SMATed sample which weren't susceptible to carbide precipitation because of their regular and coherent atomic structure and extreme low grain boundary energy as compared with those of other grain boundaries.

Fluorinated FeF3 catalyst interactions in three different oil formulations using design of experiment optimization and chemistry characterization of tribofilms

ABSTRACTThe influence of fluorinated FeF3 catalyst on the formation and properties of tribofilms was examined using design of experiment (DOE) under extreme boundary lubrication (385 N or maximum Hertzian contact pressure of 2.72 GPa). A closed loop boundary condition test was developed to examine the behaviour of lubricants under boundary conditions. The reduction of phosphorus in engine oil was examined using two different plain oils and one fully formulated oil. Results indicate the formation of a thicker tribofilm in plain fluorinated oil when compared with fluorinated fully formulated oils.Several chemistry combinations were prepared and tested. Wear and frictional properties were evaluated using DOE, and the interactions of fluorinated FeF3 catalyst with minimum phosphorus were studied and compared with respect to fully formulated and plain zinc dialkyl dithiophosphate oils. Tribofilms with thickness ranging from 150 to 350 nm were developed during wear tests and were analysed for fluorinated plain and fully formulated oils that target reducing phosphorus. Three specific tests with optimised 0.6% FeF3 catalyst concentrations were used with 0.05% phosphorus in plain and fully formulated oil to verify the model optimised conditions with respect to wear and time to full break down. Scanning electron microscopy, hardness of the tribofilms and Auger spectroscopy confirm the presence of fluorine and phosphorus. These tests confirm the optimised prediction of the DOE model. Copyright © 2011 John Wiley & Sons, Ltd.

Interactions of fluorinated catalyst and polutetrafluoroethylene in two different plain zinc dialkyldithiophosphate oils and one fully formulated oil using design of experiment

ABSTRACTFriction and wear performance of engine oils in the presence of polutetrafluoroethylene (PTFE) and iron fluoride (FeF3) catalyst with plain zinc dialkyldithiophosphate (ZDDP) oils, and fully formulated oils were studied under extreme boundary lubrication (2.72 Hertzian contact load). Two brands of plain ZDDP oils with the same phosphorus percentages were used in the analysis. The study uses design of experiment (DOE) to analyse and optimise the fluorinated oil combinations, thus reducing phosphorus in both plain and fully formulated oils. High and low concentrations of fluorinated catalyst were optimised, and a (PTFE + catalyst) combination suitable for plain ZDDP oil and a fully formulated oil were studied using scanning electron microscopy, energy dispersive spectroscopy, wear profile analysis and tribosurfaces comparison. The experiment indicated that submicron FeF3 catalyst played an important role in preventing the breakdown of the tribofilm.The reduction of phosphorus in engine oil was examined. Very reproducible boundary lubrication tests with three replicates for each oil blend were conducted as part of the DOE software to study the behaviour of FeF3 catalyst and PTFE or Teflon in developing environmentally friendly (reduced P and S) anti‐wear additives for future engine oil formulations. Several responses with respect to sample failure and post‐wear measurements were analysed, and the overall desirability of the model was targeted to lower phosphorus blends. The goal of the model solution was to check the maximum and minimum interactions of PTFE and selected FeF3 catalyst with respect to both plain ZDDP oils and fully formulated oil. Copyright © 2011 John Wiley & Sons, Ltd.

Numerical simulation of floating bodies in extreme free surface waves

Abstract. In this paper, we use the in-house Computational Fluid Dynamics (CFD) flow code AMAZON-SC as a numerical wave tank (NWT) to study wave loading on a wave energy converter (WEC) device in heave motion. This is a surface-capturing method for two fluid flows that treats the free surface as contact surface in the density field that is captured automatically without special provision. A time-accurate artificial compressibility method and high resolution Godunov-type scheme are employed in both fluid regions (air/water). The Cartesian cut cell method can provide a boundary-fitted mesh for a complex geometry with no requirement to re-mesh globally or even locally for moving geometry, requiring only changes to cut cell data at the body contour. Extreme wave boundary conditions are prescribed in an empty NWT and compared with physical experiments prior to calculations of extreme waves acting on a floating Bobber-type device. The validation work also includes the wave force on a fixed cylinder compared with theoretical and experimental data under regular waves. Results include free surface elevations, vertical displacement of the float, induced vertical velocity and heave force for a typical Bobber geometry with a hemispherical base under extreme wave conditions.

Optimization of Mechanism of Boundary Lubrication in Fully Formulated Commercial Engine Oil Using Design of Experiment

Design of experiment (DOE) analysis was used to study the desirability factor between contact loads, oil quantity, and surface roughness. The analysis developed a series of interactions between factors to get the best correlations between contact loads and oil quantity that leads to the stabilization of the tribofilm. A closed-loop boundary condition test was developed to examine the behavior of lubricants under boundary conditions. Polished and unpolished testing specimens were established to show the differences in friction and wear profiles under extreme boundary lubrication. The boundary condition test was very reproducible and can be used to study the mechanism of boundary lubrication. The mechanism of antiwear film formation and breakdown was followed carefully by monitoring the friction coefficient over the duration of the test and running scanning electron microscopy (SEM) on selected tests. The thickness of the boundary layer lubricant, which is determined by the concentration of additives in the supplied oil, is optimized for the polished and unpolished test cylinders. The optimized desirability shows the best loading and oil supply condition that leads to greater consistency in the breakdown of the tribofilm for a fixed contact load and fixed amount of fully formulated zinc dialkyldithiophosphate (ZDDP) oil. The number of cycles to breakdown of the protective tribofilm is also consistent with the applied load for a fixed thickness of the boundary lubrication film. It is evident that at lower contact loads a stable tribofilm rich in phosphorous is formed, whereas at higher contact loads the breakdown of the tribofilm results in wear debris and higher sulfur content on the wear surface.

Determination of the Nitrous Oxide Emission Potential of Deammonification under Anoxic Conditions

Various studies have been performed to determine nitrous oxide (N2O) emissions from conventional biological nitrogen removal processes in wastewater treatment like nitrification and denitrification in the main stream. However, with respect to the overall emissions of a wastewater treatment plant, part-stream treatment for high-strength wastewater (e.g., sludge liquor) is also expected to hold a significant emission potential because of high concentrations and extreme boundary conditions. This paper presents results from a laboratory-scale study on nitrous oxide production by biomass from a deammonification process (nitritation + anammox) under anoxic conditions. It was discovered that N2O formation results from incomplete endogenous denitrification rather than anammox and is dependent on substrate availability. Based on direct measurements of the dissolved N2O concentrations in a sequencing batch reactor, the dynamic behavior of N2O production is characterized in more detail. The results show that, during anoxic conditions, the N2O emission potential of deammonification is significantly lower than from conventional denitrification.

Mechanism of wear at extreme load and boundary conditions with ashless anti-wear additives: Analysis of wear surfaces and wear debris

Ashless antiwear additives have begun to find applications in automotive and heavy industry applications as sludge formation is reduced leading to improved efficiency. In this study, six different ashless antiwear agents, including an ashless neutral dialkyl dithiophosphate (DDP-1), an acidic dialkyl dithiophosphate (DDP-2), an alkylated triphenyl phosphorothionate (A-TPPT), a butylated triphenyl phosphorothionate (B-TPPT), a triphenyl phosphorothionate (H-TPPT), and an amine phosphate (AP-1) were studied. Conditions of tribotesting were chosen to simulate harsh boundary lubrication where extreme loads are applied and the anti-wear additives are stressed. These test conditions can potentially separate out high performing additives from ones that provide marginal protection. The mechanism of wear in the best-case scenario with acidic dialkyl dithiophosphate was associated with the formation of well-developed tribofilms even under the harsh conditions. On the other hand the neutral dialkyl dithiophosphate exhibited severe abrasive wear and premature failure. The amine phosphate, while it has a functioning tribofilm, also exhibited weak adhesion of the tribofilm resulting in stick slip behavior and extensive polishing wear. All the phosphorothionates exhibited poor wear outcomes with the alkylated triphenyl phosphorothionate being the best and the protonated triphenyl phosphorothionate being the worst. The mechanism of wear in the phosphorothionates was associated with polishing wear in A-TPPT and B-TPPT where wear debris trapped between contacting surfaces removes the tribofilms that form on the surface and abrasive wear in the case of H-TPPT. Transmission electron microscopy of the harvested wear debris indicated the formation of amorphous debris with embedded nanocrystalline particles that were identified as Fe3O4 in most of the cases. The wear protection afforded by the anti-wear additive can be correlated with the number of the nanocrystalline oxide particles embedded in the debris with the ones with smallest number of oxide particles exhibiting the best wear performance.

Ranks of operators in simple [formula omitted]-algebras

Let A be a unital simple separable C ∗ -algebra with strict comparison of positive elements. We prove that the Cuntz semigroup of A is recovered functorially from the Murray–von Neumann semigroup and the tracial state space T ( A ) whenever the extreme boundary of T ( A ) is compact and of finite covering dimension. Combined with a result of Winter, we obtain Z ⊗ A ≅ A whenever A moreover has locally finite decomposition rank. As a corollary, we confirm Elliott's classification conjecture under reasonably general hypotheses which, notably, do not require any inductive limit structure. These results all stem from our investigation of a basic question: what are the possible ranks of operators in a unital simple C ∗ -algebra?

A dislocation dynamics based higher-order crystal plasticity model and applications on confined thin-film plasticity

A higher-order crystal plasticity model based on the continuum description of dislocation dynamics is developed to investigate the confined thin-film plasticity at micro-scale. In this model the “back stress” and the “slip resistance” for each slip system are incorporated into a standard diffusion equation for crystal slip, which accounts for the motion of dislocations in a continuum level. Furthermore, a surface energy based interfacial model is introduced here to take account of the interaction between dislocations and the interface. It can provide a more comprehensive study of the interface effect on the confined crystal plastic behavior rather than the two extreme boundary models used in other higher-order crystal plasticity models in which the dislocations can freely or hardly pass through the crystal interface. Then by implementing these models into finite element code the tensions of single-crystal/polycrystal thin Al films with passivation layers are numerically investigated. Two hardening factors associated respectively with the “back stress” and “slip resistance” are qualitatively studied, and it can be concluded from present study that the “back stress” hardening may dominate the strengthening of flow stress in confined thin-film plasticity at sub-micro scale. The interfacial model is applied to successfully model the interactions of dislocation with the film-passivation interfaces.

Extreme electromagnetic boundary conditions and their manifestation at the inner surfaces of spherical and cylindrical cloaks

Generalized electromagnetic boundary conditions are derived for interfaces containing surface layers of electric and magnetic polarization. Next, the singularities in the fields and polarization densities at the inner surfaces of spherical and circular cylindrical cloaks illuminated by sources inside the cavities of the cloaks are determined from a plane-wave analysis of fields incident on a half space of material characterized by a relative permittivity–permeability dyadic equal to that of the inner material surfaces of the cloaks. Lastly, these singular fields and polarization densities are shown to satisfy the generalized boundary conditions. For sources inside the cloak cavities, it is found that the inner surfaces of spherical cloaks, unlike the inner surfaces of cylindrical cloaks, behave as “DB boundaries” at which n ˆ ⋅ D and n ˆ ⋅ B are zero.

A unifying explanation for diverse metabolic scaling in animals and plants

The scaling of metabolic rate with body mass has long been a controversial topic. Some workers have claimed that the slope of log-log metabolic scaling relationships typically obeys a universal 3/4-power law resulting from the geometry of resource-transport networks. Others have attempted to explain the broad diversity of metabolic scaling relationships. Although several potentially useful models have been proposed, at present none successfully predicts the entire range of scaling relationships seen among both physiological states and taxonomic groups of animals and plants. Here I argue that our understanding may be aided by three shifts in focus: from explaining average tendencies to explaining variation between extreme boundary limits, from explaining the slope and elevation (metabolic level) of scaling relationships separately to showing how and why they are interrelated, and from focusing primarily on internal factors (e.g. body design) to a more balanced consideration of both internal and external (ecological) factors. By incorporating all of these shifts in focus, the recently proposed metabolic-level boundaries hypothesis appears to provide a useful way of explaining both taxonomic and physiological variation in metabolic scaling relationships. This hypothesis correctly predicts that the scaling slope should vary mostly between 2/3 and 1 and that it should be related to metabolic (activity) level according to an approximately U-shaped function. It also implies that the scaling of other energy-dependent biological processes should be related to the metabolic level of the organisms being examined. Some data are presented that support this implication, but further research is needed.

Threshold behaviour in hydrological systems as (human) geo-ecosystems: manifestations, controls, implications

Abstract. In this paper we review threshold behaviour in environmental systems, which are often associated with the onset of floods, contamination and erosion events, and other degenerative processes. Key objectives of this review are to a) suggest indicators for detecting threshold behavior, b) discuss their implications for predictability, c) distinguish different forms of threshold behavior and their underlying controls, and d) hypothesise on possible reasons for why threshold behaviour might occur. Threshold behaviour involves a fast qualitative change of either a single process or the response of a system. For elementary phenomena this switch occurs when boundary conditions (e.g., energy inputs) or system states as expressed by dimensionless quantities (e.g. the Reynolds number) exceed threshold values. Mixing, water movement or depletion of thermodynamic gradients becomes much more efficient as a result. Intermittency is a very good indicator for detecting event scale threshold behavior in hydrological systems. Predictability of intermittent processes/system responses is inherently low for combinations of systems states and/or boundary conditions that push the system close to a threshold. Post hoc identification of "cause-effect relations" to explain when the system became critical is inherently difficult because of our limited ability to perform observations under controlled identical experimental conditions. In this review, we distinguish three forms of threshold behavior. The first one is threshold behavior at the process level that is controlled by the interplay of local soil characteristics and states, vegetation and the rainfall forcing. Overland flow formation, particle detachment and preferential flow are examples of this. The second form of threshold behaviour is the response of systems of intermediate complexity – e.g., catchment runoff response and sediment yield – governed by the redistribution of water and sediments in space and time. These are controlled by the topological architecture of the catchments that interacts with system states and the boundary conditions. Crossing the response thresholds means to establish connectedness of surface or subsurface flow paths to the catchment outlet. Subsurface stormflow in humid areas, overland flow and erosion in semi-arid and arid areas are examples, and explain that crossing local process thresholds is necessary but not sufficient to trigger a system response threshold. The third form of threshold behaviour involves changes in the "architecture" of human geo-ecosystems, which experience various disturbances. As a result substantial change in hydrological functioning of a system is induced, when the disturbances exceed the resilience of the geo-ecosystem. We present examples from savannah ecosystems, humid agricultural systems, mining activities affecting rainfall runoff in forested areas, badlands formation in Spain, and the restoration of the Upper Rhine river basin as examples of this phenomenon. This functional threshold behaviour is most difficult to predict, since it requires extrapolations far away from our usual experience and the accounting of bidirectional feedbacks. However, it does not require the development of more complicated model, but on the contrary, only models with the right level of simplification, which we illustrate with an instructive example. Following Prigogine, who studied structure formation in open thermodynamic systems, we hypothesise that topological structures which control response thresholds in the landscape might be seen as dissipative structures, and the onset of threshold processes/response as a switch to more efficient ways of depleting strong gradients that develop in the case of extreme boundary conditions.

Global biogeophysical interactions between forest and climate

In two sensitivity experiments using the Earth System Model of the Max Planck Institute for Meteorology (MPI‐ESM), the vegetation cover of the ice‐free land surface has been set worldwide to either forest or grassland in order to quantify the quasi‐equilibrium response of the atmosphere and ocean components to extreme land surface boundary conditions. After 400 years of model integration, the global mean annual surface temperature increased by 0.7°K and declined by 0.6°K in the forest and grassland simulations, respectively, as compared to the control simulation. Thereafter, the geographic distribution of vegetation has been allowed to respond interactively to climate. After subsequent 500 years of interactive climate‐vegetation dynamics, both forest and grassland simulations converged to essentially the same climate state as in the control simulation. This convergence suggests an absence of multiple climate‐forest states in the current version of the MPI‐ESM.

Fluxes of climate‐relevant trace gases between a Norway spruce forest soil and atmosphere during repeated freeze–thaw cycles in mesocosms

AbstractFor this century, an increasing frequency of extreme meteorological boundary conditions is expected, presumably resulting in a changing frequency of freezing and thawing of soils in higher‐elevation areas. Our current knowledge about the effects of these events on trace‐gas emissions from soils is scarce. In this study, the effects of freeze–thaw events on the fluxes of the trace gases CO2, N2O, and NO between soil and atmosphere were investigated in a laboratory experiment. Undisturbed soil columns were collected from a mature Norway spruce forest in the “Fichtelgebirge”, SE Germany. The influence of freezing temperatures (–3°C, –8°C, –13°C) on gas fluxes was studied during the thawing periods (+5°C) in three freeze–thaw cycles (FTCs) and compared to unfrozen controls (+5°C).Two different types of soil columns were examined in parallel—one consisting of O layer only (O columns) and one composed of O layer and mineral soil horizons (O+M columns)—to quantify the contribution of the organic layer and the top mineral soil to the production or consumption of these trace gases.During the thawing period, we observed increasing emissions of CO2, N2O, and NO from the spruce forest soil, but the cumulative emissions of these gases did mostly not exceed the level of the controls. The results show that the O layers were mainly involved in the gas production. Severe soil frost increased CO2 fluxes during soil thawing, whereas repetition of the freeze–thaw events decreased CO2 fluxes from the thawing soil. Fluxes of N2O and NO were neither influenced by freezing temperature nor by freeze–thaw repetition.Stable‐isotope analysis indicated that denitrification was mostly responsible for the N2O production in the FTC columns. Furthermore, isotope data demonstrated a consumption of N2O through microbial denitrification to N2. It was further shown, that production of N2O also occurred in the mineral horizons. The NO emissions were mainly driven by increasing soil temperature during thawing. In this freeze–thaw experiment up to 20 times higher NO than N2O fluxes were recorded. Our results suggest that topsoil thawing has little potential to increase the emissions of CO2, N2O, and NO in spruce forest soils.

Metric Subregularity and Constraint Qualifications for Convex Generalized Equations in Banach Spaces

Several notions of constraint qualifications are generalized from the setting of convex inequality systems to that of convex generalized equations. This is done and investigated in terms of the coderivatives and the normal cones, and thereby we provide some characterizations for convex generalized equations to have the metric subregularity. As applications, we establish formulas of the modulus of calmness and provide several characterizations of the calmness. Extending the classical concept of extreme boundary, we introduce a notion of recession cores of closed convex sets. Using this concept, we establish global metric subregularity (i.e., error bound) results for generalized equations.

Clinical Trials in the Wake of Vioxx

Clinical trials have become the preeminent tool for investigating new diagnostic, therapeutic, and preventive treatment strategies. During these trials, periodic interim data analyses are conducted by data monitoring committees (DMCs) to ensure participant safety. If accumulated data indicate harm to participants, clear evidence of superior efficacy, or futility of collecting additional data, studies may be terminated before their planned conclusion. Editorial p 2173 These termination decisions are invariably complex and involve important subjective and ethical elements.1 Of greatest concern when studies are terminated because of clear benefit is the possibility that the superior intervention has toxicities that remain undiscovered. Early termination entails the abbreviation of clinical experience that would permit assessment of the longer-term safety profile. However, study continuation when treatments are not equally effective also means that some participants will continue to receive a less effective therapy. The tension between protecting both trial participants and future patients has been increasingly acute since rofecoxib (Vioxx [Merck]) and other cyclooxygenase-2 inhibitors were implicated in a greater risk of myocardial infarction. Thrombotic side effects of cyclooxygenase-2 inhibition were postulated as a result of the propensity for selective antagonists to decrease vascular prostacyclin production and possibly affect the balance between prothrombotic and antithrombotic eicosanoids.2 Little evidence of toxicity was evident in preapproval trials, however, and rofecoxib was approved in 1999 for relief of the signs and symptoms of osteoarthritis, the management of acute pain, and the treatment of primary dysmennorhea.3 The possibility of cardiac toxicity in human trials was recognized in the Vioxx Gastrointestinal Outcomes Research (VIGOR) trial.4 Meta-analyses, database studies, and prospective trials further corroborated cardiac toxicity,5–8 and Merck voluntarily withdrew rofecoxib from the US market on September 30, 2004,9 amid widespread criticism of both Merck and the Food and Drug Administration.10,11 In the wake …

Three-dimensional finite/infinite elements analysis of fluid flow in porous media

Fluid flow in naturally fractured porous media can always be regarded as an unbounded domain problem and be better solved by finite/infinite elements. In this paper, a three-dimensional two-direction mapped infinite element is generated and combined with conventional finite elements and one direction infinite element to simulate poroelasticity. Therefore, the entire semi-infinite domain can be included in the numerical analysis. Both single- and dual-porosity porous media are considered. For the purpose of validation, we compare the results of finite/infinite elements with those of finite elements under two extreme boundary conditions. The comparison indicated that mapped infinite element is an appropriate approach to model fluid flow in porous media and provides an intermediate solution.

Grain Boundary Nature and Localized Corrosion in 304 Austenitic Stainless Steel

The present study had one broad objective – to systematically characterize effects of overall grain boundary nature on localized corrosion, intergranular corrosion (IGC) and stress corrosion cracking (IGSCC), of type 304 (UNS S 30400) austenitic stainless steel. Various combinations of cold rolling and solution annealing, were applied to alter relative the relative concentrations of ‘special’ or low CSL boundaries and to relate them with the local corrosion resistance, IGC and IGSCC, after respective sensitization treatments. It has been shown that both extreme high and low concentration of random (or high energy) boundaries can provide an effective means of control for localized corrosion, degree of sensitization (DOS), IGC and IGSCC, - the improvement in localized corrosion resistance at extreme grain boundary randomization being more effective.

Spectroscopic Properties of Cool Stars in the Sloan Digital Sky Survey: An Analysis of Magnetic Activity and a Search for Subdwarfs

We present a spectroscopic analysis of nearly 8000 late-type dwarfs in the Sloan Digital Sky Survey. Using the Halpha emission line as an activity indicator, we investigate the fraction of active stars as a function of spectral type and find a peak near type M8, confirming previous results. In contrast to past findings, we find that not all M7-M8 stars are active. We show that this may be a selection effect of the distance distributions of previous samples, as the active stars appear to be concentrated near the Galactic Plane. We also examine the activity strength (ratio of the luminosity emitted in Halpha to the bolometric luminosity) for each star, and find that the mean activity strength is constant over the range M0-M5 and declines at later types. The decline begins at a slightly earlier spectral type than previously found. We explore the effect that activity has on the broadband photometric colors and find no significant differences between active and inactive stars. We also carry out a search for subdwarfs using spectroscopic metallicity indicators, and find 60 subdwarf candidates. Several of these candidates are near the extreme subdwarf boundary. The spectroscopic subdwarf candidates are redder by \~0.2 magnitudes in g-r compared to disk dwarfs at the same r-i color.

Majorants and Extreme Points of Unit Balls in Bernstein Spaces

The Bernstein space Bp (σ) (1\( \leqslant p \leqslant \infty ,\sigma >\)0) is the set of functions from Lp(\(\mathbb{R}\)) having Fourier transforms (in the sense of generalized functions) with supports in the compact segment [-σ , σ ]. Every function f\( \in B^p (\sigma )\) has an analytic continuation onto the complex plane, which is an entire function of exponential type ≤ σ. The spaces Bp (σ)\, are conjugate Banach spaces. Therefore, the closed unit ball \(\mathcal{D}(B^p (\sigma ))\) in Bp (σ) has a rich set of extreme (boundary) points: \(\mathcal{D}(B^p (\sigma ))\) coincides with the weakly * closed convex hull of its extreme points. Since, for 1< p< ∞, Bp (σ) is a uniformly convex space, only the balls \(\mathcal{D}(B^1 (\sigma ))\) and \(\mathcal{D}(B^\infty (\sigma ))\) have nontrivially arranged sets of extreme points. In this paper, in terms of zeros of entire functions, we obtain necessary and sufficient conditions of extremeness for functions from \(\mathcal{D}(B^1 (\sigma ))\).