TEM observations of wear mechanisms of TiAlCrN and TiAlN/CrN coatings grown by combined steered-arc/unbalanced magnetron deposition

The dry sliding wear of monolayer TiAlCrN and TiAlCrYN and multilayer TiAlN/CrN coatings has been investigated against a BM2 tool steel counterface using a ring on block configuration at 91 N, 0.42 m/s. The coatings were deposited on a BM2 tool steel substrate by combined steered-arc/unbalanced-magnetron deposition. The wear rate of the multilayer was superior to the monolayer, although both provide a substantial improvement compared with the wear behaviour of the base BM2 tool steel (e.g., wear rate = 6.1 × 10-4 mm3/m for the BM2 tool steel; 3.98 × 10-5 mm3/m for the TiAlCrN monolayer and 2.58 × 10-5 mm3/m for the TiAlN/CrN multilayer). Wear of the coatings occurred by several mechanisms, fine scale (< 200 nm) detachment in the early stages and micron scale detachment associated with cracking in the coating in the later stages. Detailed transmission electron microscopy of cross-sections of the worn surface indicated that two dominant types of cracking were present within the coating: (1) cracking perpendicular to the coating surface, often along columnar grain boundaries, typically running through the entire coating; (2) cracking approximately parallel to the worn surface, extending across several columnar grains. For the multilayers, there was no evidence that the spalling was induced by decohesion along the interface of the multilayers. Limited surface deformation was detected at the worn surface of the TiAlCrYN and TiAlCrN, but not at the worn surface of the TiAlN/CrN, tested under identical conditions. In contrast, the uncoated BM2 tool steel worn surface exhibited extensive plastic deformation. The relationship between wear mechanism and coating structure is discussed. © 1999 Published by Elsevier Science S.A. All rights reserved

Investigating worn surfaces of nanoscale TiAlN/VN multilayer coating using FIB and TEM

TiAlN/VN multilayer coatings exhibit excellent dry sliding wear resistance and low friction coefficient, believed to be associated with the formation of tribo-films comprising Magnéli phases such as V2O5. In order to investigate this hypothesis, dry sliding wear of TiAlN/VN coatings was undertaken against Al2O3. Focused ion beam was used to generate site-specific TEM specimens. A thin (2-20nm) tribo-film was observed at the worn surface, with occasional 'roll-like' wear debris (φ 5-40nm). Both were amorphous and contained the same Ti, Al and V ratio as the coating, but with the nitrogen largely replaced by oxygen. No evidence of Magnéli phases was found. © 2006 IOP Publishing Ltd

TiAIN based nanoscale multilayer coatings designed to adapt their tribological properties at elevated temperatures

The addition of properly selected elements, coupled in nanoscale multilayer structures, can further enhance the properties of TiAlN coatings and bring new high performance. The incorporation of Y in the nanoscale pseudo-superlattice TiAlCrN/TiAlYN with typical period of 1.7 nm not only improves the oxidation resistance but also effectively reduces the coefficient of friction of the coating from 0.9 to 0.65 at temperatures in the range of 850–950 °C. The adaptation of the tribological properties occurs as a result of the preferential migration of the Y to the column boundaries. TiAlN/VN superlattice can achieve another self-adaptation process. During friction the coatings adapt themselves to the combined thermal and mechanical wear by the formation of highly lubricious vanadium-oxides due to high flash temperatures at the asperity contacts on the surface. The integrity of the bulk of the coating is retained, leading to exceptionally low, for superhard coatings, friction coefficient of 0.5 and a wear coefficient of 2 × 10−17 m3·N−1·m−1. The coatings have been deposited by the combined steered cathodic arc unbalanced magnetron sputtering method.</p

Conformational studies of the tetramerization site of human erythroid spectrin by cysteine-scanning spin-labeling EPR methods

We used cysteine-scanning and spin-labeling methods to prepare singly spin labeled recombinant peptides for electron paramagnetic resonance studies of the partial domain regions at the tetramerization site (N-terminal end of α and C-terminal end of β) of erythroid spectrin. The values of the inverse line width parameter (ΔH0-1) from a family of SpoI-1-368Δ peptides scanning residues 21-30 exhibited a periodicity of ∼3.5-4. We used molecular dynamics calculations to show that the asymmetric mobility of this helix is not necessarily due to tertiary contacts, but is likely due to intrinsic properties of helix C′, a helix with a heptad pattern sequence. The residues with low ΔH0-1 values (residues at positions 21, 25, and 28/29) were those on the hydrophobic side of this amphipathic helix. Native gel electrophoresis results showed that these residues were functionally important and are involved in the tetramerization process. Thus, EPR results readily identified functionally important residues in the α spectrin partial domain region. Mutations at these positions may lead to clinical symptoms. Similarly, the ΔH0-1 values from a family of spin-labeled SpβI-1898-2083Δ peptides also exhibited a periodicity of ∼3.5-4, indicating a helical conformation in the two scanned regions (residues 2008-2018 and residues 2060-2070). However, the region consisting of residues 2071-2076 was in a disordered conformation. Both helical regions include a hydrophilic side with high ΔH0-1 values and a hydrophobic side with low ΔH0-1 values, demonstrating the amphipathic nature of the helical regions. Residues 2008, 2011, 2014, and 2018 in the first scanned region and residues 2061, 2065, and 2068 in the second scanned region were on the hydrophobic side. These residues were critical in αβ spectrin association at the tetramerization site. Mutations at some of these positions have been reported to be detrimental in clinical studies. © 2005 American Chemical Society

A liquid helium target system for a measurement of parity violation in neutron spin rotation

A liquid helium target system was designed and built to perform a precision measurement of the parity-violating neutron spin rotation in helium due to the nucleon-nucleon weak interaction. The measurement employed a beam of low energy neutrons that passed through a crossed neutron polarizer--analyzer pair with the liquid helium target system located between them. Changes between the target states generated differences in the beam transmission through the polarizer--analyzer pair. The amount of parity-violating spin rotation was determined from the measured beam transmission asymmetries. The expected parity-violating spin rotation of order $10^{-6}$ rad placed severe constraints on the target design. In particular, isolation of the parity-odd component of the spin rotation from a much larger background rotation caused by magnetic fields required that a nonmagnetic cryostat and target system be supported inside the magnetic shielding, while allowing nonmagnetic motion of liquid helium between separated target chambers. This paper provides a detailed description of the design, function, and performance of the liquid helium target system.Comment: V2: 29 pages, 14 figues, submitted to Nucl. Instrum. Meth. B. Revised to address reviewer comment

Collisions of particles in locally AdS spacetimes II Moduli of globally hyperbolic spaces

We investigate 3-dimensional globally hyperbolic AdS manifolds containing "particles", i.e., cone singularities of angles less than $2\pi$ along a time-like graph $\Gamma$. To each such space we associate a graph and a finite family of pairs of hyperbolic surfaces with cone singularities. We show that this data is sufficient to recover the space locally (i.e., in the neighborhood of a fixed metric). This is a partial extension of a result of Mess for non-singular globally hyperbolic AdS manifolds.Comment: 29 pages, 3 figures. v2: 41 pages, improved exposition. To appear, Comm. Math. Phys. arXiv admin note: text overlap with arXiv:0905.182

TEM-EELS study of low-friction superlattice TiAlN/VN coating: the wear mechanisms

A 20-50 nm thick tribofilm was generated on the worn surface of a multilayer coating TiAlN/VN after dry sliding test against an alumina counterpart. The tribofilm was characterized by applying analytical transmission electron microscopy techniques with emphasis on detailed electron energy loss spectrometry and energy loss near edge structure analysis. Pronounced oxygen in the tribofilm indicated a predominant tribo-oxidation wear. Structural changes in the inner-shell ionization edges of N, Ti and V suggested decomposition of nitride fragments

Final state interactions in the decay B0→ηcK∗B^0 \to \eta_c K^*

In this article, we study the final-state rescattering effects in the decay $B^0 \to \eta_cK^*$, the numerical results indicate the corrections are comparable with the contribution from the naive factorizable amplitude, and the total amplitudes can accommodate the experimental data.Comment: 11 pages, 1 figure, revised version, to appear in EPJ

Semileptonic decays of Bs1B_{s1}, Bs2∗B_{s2}^*, Bs0B_{s0} and Bs1′B_{s1}'

Stimulated by recent observations of the excited bottom-strange mesons $B_{s1}$ and $B_{s2}^*$, we calculate the semileptonic decays $B_{s0}, B_{s1}^{\prime}, B_{s1}, B_{s2}^*\to [D_s(1968), D_{s}^*(2112), D_{sJ}(2317), D_{sJ}(2460)]\ell\bar{\nu}$, which is relevant for the exploration of the potential of searching these semileptonic decays in experiment.Comment: 11 pages, 3 figures, 9 tables. More discussion added, some descriptions changed. The version to appear in EPJ

Immersed boundary-finite element model of fluid-structure interaction in the aortic root

It has long been recognized that aortic root elasticity helps to ensure efficient aortic valve closure, but our understanding of the functional importance of the elasticity and geometry of the aortic root continues to evolve as increasingly detailed in vivo imaging data become available. Herein, we describe fluid-structure interaction models of the aortic root, including the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the sinotubular junction, that employ a version of Peskin's immersed boundary (IB) method with a finite element (FE) description of the structural elasticity. We develop both an idealized model of the root with three-fold symmetry of the aortic sinuses and valve leaflets, and a more realistic model that accounts for the differences in the sizes of the left, right, and noncoronary sinuses and corresponding valve cusps. As in earlier work, we use fiber-based models of the valve leaflets, but this study extends earlier IB models of the aortic root by employing incompressible hyperelastic models of the mechanics of the sinuses and ascending aorta using a constitutive law fit to experimental data from human aortic root tissue. In vivo pressure loading is accounted for by a backwards displacement method that determines the unloaded configurations of the root models. Our models yield realistic cardiac output at physiological pressures, with low transvalvular pressure differences during forward flow, minimal regurgitation during valve closure, and realistic pressure loads when the valve is closed during diastole. Further, results from high-resolution computations demonstrate that IB models of the aortic valve are able to produce essentially grid-converged dynamics at practical grid spacings for the high-Reynolds number flows of the aortic root