Ray methods for free boundary problems

We discuss the use of the WKB ansatz in a variety of parabolic problems involving a small parameter. We analyse the Stefan problem for small latent heat, the Black–Scholes problem for an American put option, and some nonlinear diffusion equations, in each case constructing an asymptotic solution by the use of ray methods

The demise of a model? The state of collective bargaining and worker representation in Germany.

This article investigates collective bargaining trends in the German private sector since 2000. Using data from the IAB Establishment Panel and the German Establishment History Panel, it provides both cross-sectional and longitudinal evidence on these developments. It confirms that the hemorrhaging of sectoral bargaining, first observed in the 1980s and 1990s, is ongoing. Furthermore, works councils are also in decline, so that the dual system also displays erosion. For their part, any increases in collective bargaining at firm level have been minimal in recent years, while the behavior of newly-founded and closing establishments does not seem to lie at the root of a burgeoning collective bargaining free sector. Although there are few obvious signs of an organic reversal of the process, some revitalization of the bargaining system from above is implied by the labor policies of the new coalition government

Modelling the influence of the process inputs on the removal of surface contaminants from Ti-6Al-4V linear friction welds

The linear friction welding (LFW) process is finding increasing interest from industry for the fabrication of near-net-shape, titanium alloy Ti–6Al–4V, aerospace components. Currently, the removal of surface contaminants, such as oxides and foreign particles, from the weld interface into the flash is not fully understood. To address this problem, two-dimensional (2D) computational models were developed using the finite element analysis (FEA) software DEFORM and validated with experiments. The key findings showed that the welds made with higher applied forces required less burn-off to completely remove the surface contaminants from the interface into the flash; the interface temperature increased as the applied force was decreased or the rubbing velocity increased; and the boundary temperature between the rapid flash formation and negligible material flow was approximately 970 °C. An understanding of these phenomena is of particular interest for the industrialisation of near-net-shape titanium alloy aerospace components.EPSRC, Boeing Company, Welding Institut

Coarse-graining diblock copolymer solutions: a macromolecular version of the Widom-Rowlinson model

We propose a systematic coarse-grained representation of block copolymers, whereby each block is reduced to a single ``soft blob'' and effective intra- as well as intermolecular interactions act between centres of mass of the blocks. The coarse-graining approach is applied to simple athermal lattice models of symmetric AB diblock copolymers, in particular to a Widom-Rowlinson-like model where blocks of the same species behave as ideal polymers (i.e. freely interpenetrate), while blocks of opposite species are mutually avoiding walks. This incompatibility drives microphase separation for copolymer solutions in the semi-dilute regime. An appropriate, consistent inversion procedure is used to extract effective inter- and intramolecular potentials from Monte Carlo results for the pair distribution functions of the block centres of mass in the infinite dilution limit.Comment: To be published in mol.phys(2005

Lung content analysis of cases occupationally exposed to chrysotile asbestos.

The lung contents of six workers who had been occupationally exposed to chrysotile asbestos were examined. Five were lung cancer cases from Quebec, Canada. The sixth, an American worker who had developed pleural mesothelioma, was particularly interesting, with the lung content strikingly distinct from the Canadian cases; chrysotile, the predominant fiber in his lung, was present at a concentration 300 times that of the average total fiber content in the Canadian cases. The fiber length distribution of the chrysotile recovered from the U.S. mesothelioma case was indistinguishable from that of chrysotile specimens known to produce mesotheliomas in rats. It was also found that the characteristics of the calcium-magnesium-iron silicate fibers present in all six cases were not readily comparable to tremolite asbestos specimens known to induce mesotheliomas in animals

Kinetics of Surfactant Adsorption at Fluid/Fluid Interfaces: Non-ionic Surfactants

We present a model treating the kinetics of adsorption of soluble surface-active molecules at the interface between an aqueous solution and another fluid phase. The model accounts for both the diffusive transport inside the solution and the kinetics taking place at the interface using a free-energy formulation. In addition, it offers a general method of calculating dynamic surface tensions. Non-ionic surfactants are shown, in general, to undergo a diffusion-limited adsorption, in accord with experimental findings.Comment: 6 pages, 3 figures, see also cond-mat/960814

Modelling of the workpiece geometry effects on Ti–6Al–4V linear friction welds

Linear friction welding (LFW) is a solid-state joining process that is finding increasing interest from industry for the fabrication of titanium alloy (Ti–6Al–4V) preforms. Currently, the effects of the workpiece geometry on the thermal fields, material flow and interface contaminant removal during processing are not fully understood. To address this problem, two-dimensional (2D) computational models were developed using the finite element analysis (FEA) software DEFORM and validated with experiments. A key finding was that the width of the workpieces in the direction of oscillation (in-plane width) had a much greater effect on the experimental weld outputs than the cross-sectional area. According to the validated models, a decrease of the in-plane width increased the burn-off rate whilst decreasing the interface temperature, TMAZ thickness and the burn-off required to remove the interface contaminants from the weld into the flash. Furthermore, the experimental weld interface consisted of a Widmanstätten microstructure, which became finer as the in-plane width was reduced. These findings have significant, practical benefits and may aid industrialisation of the LFW process.The authors would like to thank the Engineering and Physical Sciences Research Council (EPSRC), The Boeing Company and The Welding Institute (TWI) for funding the research presented in this paper

Securing ZigBee Commercial Communications Using Constellation Based Distinct Native Attribute Fingerprinting

This work provides development of Constellation Based DNA (CB-DNA) Fingerprinting for use in systems employing quadrature modulations and includes network protection demonstrations for ZigBee offset quadrature phase shift keying modulation. Results are based on 120 unique networks comprised of seven authorized ZigBee RZSUBSTICK devices, with three additional like-model devices serving as unauthorized rogue devices. Authorized network device fingerprints are used to train a Multiple Discriminant Analysis (MDA) classifier and Rogue Rejection Rate (RRR) estimated for 2520 attacks involving rogue devices presenting themselves as authorized devices. With MDA training thresholds set to achieve a True Verification Rate (TVR) of TVR = 95% for authorized network devices, the collective rogue device detection results for SNR ≥ 12 dB include average burst-by-burst RRR ≈ 94% across all 2520 attack scenarios with individual rogue device attack performance spanning 83.32% \u3c RRR \u3c 99.81%

Using S Isotopes to Identify the Source of Gypsum in Mammoth Cave

Many of the dry passages of the cave are lined with gypsum (CaSO4�2H2O) crystals, an evaporite mineral. However, the source of the sulfur in these gypsum deposits is poorly constrained with possible sources including pyrite, sedimentary gypsum/anhydrite, and carbonate associated sulfate (“CAS”, SO42- substituted for CO3 2- in the calcite crystal lattice). The two most abundant forms of sulfur in the bedrock above and around Mammoth Cave are pyrite (FeSs) and CAS. These phases commonly have very different isotopic signatures (δ34S)* and the δ34S values of these phases can be compared to the δ34S of the gypsum to aid in identifying the source of the sulfur. Isolation of sulfur from pyrite and CAS is currently ongoing. Results from 110 gypsum crystals, 4 rocks in strata from within the caves, and 15 rocks from strata overlying the caves reveal some distinct patterns. 1) Gypsum crystals show relatively small scatter (~5‰) for samples from a single location (e.g. a 30 m2 room). 2) A significant correlation between δ34Sgypsum and elevation suggests a variable δ34Ssource over vertical distances of a few meters. 3) Microsampling of sulfur along the growth axes of single gypsum crystals shows a constant δ34S values suggesting no change in δ34S of the S source during its growth. Because the growth period of these crystals may be on the order of thousands of years, these results suggest a constant sulfate for long intervals. The relationship to δ34S of samples in a given room and elevation suggests that the source of gypsum sulfur is local, arising from lateral, rather than vertical, fluid fl ow, an important insight into the transport pathways of water in a karstic system. Sampling of pyrite and CAS is currently ongoing. *δ34S = [(34S/32Ssample)/(34S/32Sstandard)-1(x)1,000‰ where 34S and 32S are the molar ratios of each S isotope given in “per mil” (‰), equivalent to parts per thousand