There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

Tissue manipulation and securement systems are described herein. A tissue manipulation assembly is pivotably coupled to the distal end of a tubular member and has a lower jaw member and an upper jaw member pivotably coupled to the lower jaw member. A reconfigurable launch tube is also pivotably coupled to the upper jaw member and is used to urge the jaw members from a low-profile configuration to an open configuration for receiving tissue. The tissue manipulation assembly may be advanced through a shape-lockable endoscopic device, a conventional endoscope, or directly by itself into a patient. A second tool can be used in combination with the tissue manipulation assembly to engage tissue and manipulate the tissue in conjunction with the tissue manipulation assembly.

Tissue manipulation and securement system

This paper reviews previous studies on iron and steel oxidation in oxygen or air at high temperatures. Oxidation of iron at temperatures above 700°C follows the parabolic law with the development of a three-layered hematite/magnetite/wustite scale structure. However, at temperatures below 700°C, inconsistent results have been reported, and the scale structures are less regular, significantly affected by sample-preparation methods. Oxidation of carbon steel is generally slower than iron oxidation. For very short-time oxidation, the scale structures are similar to those formed on iron, but for longer-time oxidation, because of the less adherent nature, the scale structures developed are typically much more complex. Continuous-cooling conditions, after very short-time oxidation, favor the retention of an adherent scale, suggesting that the method proposed by Kofstad for deriving the rate constant using continuous cooling or heating-oxidation data is more appropriate for steel oxidation. Oxygen availability has certain effects on iron and steel oxidation. Under continuous cooling conditions, the final scale structure is found to be a function of the starting temperature for cooling and the cooling rate. Different scale structures develop across the width of a hot-rolled strip because of the varied oxygen availability and cooling rates at different locations.

Review of the High-Temperature Oxidation of Iron and Carbon Steels in Air or Oxygen

A comprehensive and integrated review of thermal barrier coatings (TBCs) applied to turbine components is provided. Materials systems, processes, applications, durability issues, technical approaches and progress for improved TBC, and our understanding of the science and technology are discussed. Thermal barrier coating prime reliance and further advances have been hampered by TBC loss by particle impact and erosion in certain locations of the turbine blades. Accumulation of low melting eutectic containing calcia, magnesia, alumina and silica resulting in TBC spallation limits maximum surface temperature. Design methodologies to address durability and data scatter issues are discussed. Compositions, morphology, characteristics and performance data for new bonds to achieve longer TBC life are described. Further reduction in the thermal conductivity of the top layer to minimise the parasitic mass of the coating on the component is being sought via top layer composition and processing modifications a...

Thermal barrier coatings technology: critical review, progress update, remaining challenges and prospects

Thermal barrier coatings (TBCs) have been in use in aeroturbine engine hot sections for over 20 years. The initial applications were driven by the need to suppress component degradation caused by excessive thermal gradients in vane airfoils. A TBC is essentially a layered, multimaterial structure that must withstand harsh temperature, environmental, thermal cycling, and stress conditions for an extended number of aircraft takeoffs and landings. A description of the TBC materials systems presently in use is presented, together with a summary of current understanding of materials and failure issues in TBCs.

Thermal Barrier Coatings for Aeroengine Applications

Thermal barrier coating (TBC) systems, needed for higher thrust with increased efficiency in gas turbines, typically consist of an alumina-scale forming metallic bond coat and a ceramic topcoat. The durability and reliability of TBC systems are critically linked to the oxidation behavior of the bond coat. Ideally, the bond coat should oxidize to form a slow-growing, non-porous and adherent thermally grown oxide (TGO) scale layer of α-Al2O3. The ability to promote such ideal TGO formation depends critically on the composition and microstructure of the bond coat, together with the presence of minor elements (metal and non-metal) that with time diffuse into the coating from the substrate during service. An experimental program was undertaken to attain a more detailed fundamental understanding of the phase equilibria in the Ni-Al-Pt system and the influences of alloy composition on the formation, growth and spallation behavior of the resulting TGO scales formed during isothermal and thermal cycling tests at 1150°C. Additional studies were conducted to determine the influence of platinum on interdiffusion behavior in the Ni-Al system, and how this influence would impact coating/substrate interdiffusion. It will be shown that platinum has a profound effect on the oxidation and interdiffusion behaviors, to the extent that novel advanced coating systems can be developed. Introduction The demand for improved performance in high-temperature mechanical systems has led to increasingly severe operating environments, particularly for the components in advanced gas-turbine engines. Future improvements in gas-turbine performance will require even higher operating efficiencies, longer operating lifetimes, reduced emissions and, therefore, higher turbine operating temperatures. Advanced cooling schemes coupled with thermal barrier coatings (TBCs) can enable the current families of nickel-base superalloys to meet the materials needs for the engines of tomorrow. Thermal barrier coating systems currently provide average metal temperature reductions of about 80°C, while potential benefits are estimated to be greater than 170°C. However, lack of reliability, more than any other design factor, limits the general use of TBC systems for gas turbines. Commercial advanced TBC systems are typically two-layered, consisting of a ceramic topcoat and an underlying metallic bond coat. The properties of the ceramic topcoat are such that it has a low thermal conductivity, high oxygen permeability, and a relatively high coefficient of thermal expansion. The topcoat is also made “strain tolerant” by depositing a structure that contains numerous pores and/or pathways. The consequently high oxygen permeability of the topcoat imposes the constraint that the metallic bond coat must be resistant to oxidation attack. The bond coat should therefore be sufficiently rich in aluminum to form a protective, thermally grown oxide (TGO) scale of α-Al2O3. In addition to imparting oxidation resistance, the TGO serves to bond the ceramic topcoat to the substrate/bond coat system. Notwithstanding, it is generally found that spallation and/or cracking of the growing TGO scale is the ultimate failure mechanism of Materials Science Forum Online: 2004-08-15 ISSN: 1662-9752, Vols. 461-464, pp 213-222 doi:10.4028/www.scientific.net/MSF.461-464.213 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,15:01:32) commercial TBCs, particularly EB-PVD TBCs [1-3]. Thus, improving the adhesion and integrity of the interfacial TGO scale is critical to the development of more reliable TBCs. Current bond coats are typically either an MCrAlY overlay (where M = Ni,Co, or both) or a platinum-modified diffusion aluminide (β-NiAl-Pt). The composition and phase constitutions of such bond coats vary. Both the MCrAlY and NiAl-Pt types of coating were originally developed to enhance long-term oxidation and corrosion protection of turbine components rather than specifically as bond coats. The oxidation resistance provided by these coatings allowed alloy developers to maximize the high-temperature mechanical properties of nickel-base superalloys. The original coatings required a high aluminum content in order to ensure re-healing of the Al2O3 scale after repeated cracking and spalling during service. In the case of TBC systems, however, Al2O3 healing after scale spallation is not an important requirement for ceramic topcoat adhesion. This is because the adhesion, and therefore the reliability, of a TBC system is dictated primarily by the first spallation event of the TGO scale. As a consequence, the currently used bond coats do not necessarily possess optimum compositions and/or structures for prime reliant TBC systems. In assessing a given bond coat system, it is also important to realize that its composition and structure change with time in service due to both TGO-scale growth and interdiffusion with the substrate. The occurrence of coating/substrate interdiffusion decreases the concentration of aluminum in the coating, thereby reducing the ability of the coating to sustain exclusive Al2O3-scale growth, particularly in the event of localized detachment and/or microcracking, and introduces unwanted elements (e.g., sulfur and titanium) which can promote oxide-scale spallation [4]. A further consequence of coating/substrate interdiffusion, particularly for the next generation of superalloys with up to 6 wt.% rhenium, is the formation of topologically close-packed (TCP) phases in the region of the original coating/substrate interface, which can be deleterious to the mechanical properties of the superalloy substrate. The results presented in this paper are from a larger US Office of Naval Research sponsored study that is concerned with gaining a more detailed fundamental understanding of the influences of alloy composition and microstructure on the adhesion/spallation resistance of TGO scales for the purpose of improving the reliability and durability of advanced TBC systems. An experimental approach was taken initially, from which the important chemical and microstructural factors governing TGO growth and adhesion were determined. The starting point for this study was a determination of the (partial) Ni-Al-Pt phase diagram, which to date has only been shown to be speculative [5] (see Fig.1). Oxidation and interdiffusion experiments were then conducted on the various Ni-Al-Pt bulk alloys processed to determine the potential effects of phase constitution and Pt content on overall coating performance. Experimental Procedures Ni-Al-Pt alloys were prepared by argon arc melting high-purity pieces of the constituents. To ensure homogenization and equilibration, all alloys were annealed at 1100 ̊C or 1150 ̊C for at least one week in a flowing argon atmosphere and then quenched in water to retain their high-temperature structure. The alloys were then cut into coupon samples and polished to a 600-grit finish for the further testing. The equilibrated alloy samples were first analyzed using X-ray diffraction (XRD) for phase identification and then prepared for metallographic analyses by cold mounting them in an epoxy resin followed by polishing to a 0.5 μm finish. Microstructure observations were initially carried out on etched samples using an optical microscope. Concentration profiles were obtained from unetched (i.e., re-polished) samples by either energy (EDS) or wavelength (WDS) dispersive spectrometry, with the former utilizing a scanning electron microscope (SEM) and the latter an 214 High Temperature Corrosion and Protection of Materials 6

Effects of Platinum on the Interdiffusion and Oxidation Behavior of Ni-Al-Based Alloys

In this paper we provide empirical evidence that using humanlike gaze cues during human-robot handovers can improve the timing and perceived quality of the handover event. Handovers serve as the foundation of many human-robot tasks. Fluent, legible handover interactions require appropriate nonverbal cues to signal handover intent, location and timing. Inspired by observations of human-human handovers, we implemented gaze behaviors on a PR2 humanoid robot. The robot handed over water bottles to a total of 102 naive subjects while varying its gaze behaviour: no gaze, gaze designed to elicit shared attention at the handover location, and the shared attention gaze complemented with a turntaking cue. We compared subject perception of and reaction time to the robot-initiated handovers across the three gaze conditions. Results indicate that subjects reach for the offered object significantly earlier when a robot provides a shared attention gaze cue during a handover. We also observed a statistical trend of subjects preferring handovers with turn-taking gaze cues over the other conditions. Our work demonstrates that gaze can play a key role in improving user experience of human-robot handovers, and help make handovers fast and fluent.Categories and Subject Descriptors I.2.9 [Robotics]: Operator interfaces, Commercial robots and applications; H.1.2 [User/Machine Systems]: Human FactorsGeneral TermsExperimentation, Design, Human Factors, Verification.

Meet me where i'm gazing: how shared attention gaze affects human-robot handover timing

This article discusses general strategies for designing alloys to form protective oxide scales. Approaches based on classical alloyoxidation theories work reasonably well for single-phase alloys. However, high-temperature alloy development has been and will increasingly be based on multiphase microstructures in order to achieve many of the needed, but usually opposing properties, such as high-temperature strength and room-temperature toughness. No theoretical-based, well-defined strategies exist for the design of oxidation-resistant multiphase alloys. Still, key factors are beginning to emerge, which can provide guidance for promoting the formation of protective scales on multiphase alloys and for taking advantage of some unique mechanisms that are operative in multiphase alloys but not in single-phase alloys.

Alloy design strategies for promoting protective oxide-scale formation

Oxidation of Al2O3 scale-forming alloys is of immense technological significance and has been a subject of much scientific inquiry for decades. The oxidation reaction is remarkably complex, involving issues of alloy composition, kinetics, thermodynamics, microstructure, mechanics and mechanical properties, crystallography, etc. A brief overview of the formation of passivating, thermally grown oxide Al2O3 scales will be given in the light of recent findings on the defect structure and associated transport behavior of α-Al2O3. It is inferred that the electronic structure of Al2O3 is of direct relevance to understand the Al2O3 scale growth. We also discuss the effect of the so-called “reactive” elements (REs)—Y, Zr, and Hf—on reducing the rate of Al2O3 scale thickening by reducing the outward flux of aluminum. An important aspect of the “new perspective” is the suggestion that the REs change the electronic structure of Al2O3—the relevant near-band-edge defect (grain boundary) states that are crucial to vacancy creation both at the scale/gas and scale/metal interfaces.

Brian Gleeson

Papers

Thermal Barrier Coatings for Aeroengine Applications

Effects of Platinum on the Interdiffusion and Oxidation Behavior of Ni-Al-Based Alloys

Meet me where i'm gazing: how shared attention gaze affects human-robot handover timing

Alloy design strategies for promoting protective oxide-scale formation

Alumina Scale Formation: A New Perspective