Complex resonances of conducting spheres with lossy coatings

The electromagnetic scattering amplitude for metal objects coated with a lossless dielectric exhibits a large number of resonances versus real frequency. These resonances are a function of the object shape and size, coating thickness, and coating electrical properties. Previously, it was shown that for coated spheres and nonspherical bare objects, these resonances can be understood in terms of phase matched circumnavigating surface waves and the objects' complex eigenfrequencies. The effect of dielectric loss in the coating on the complex eigenfrequencies and phase velocities of these surface waves is presented for a metal sphere coated with a uniform homogeneous dielectric coating. It is seen that the positions of the complex resonance frequencies move away from the real frequency axis under the influence of dielectric loss in the coating. The effect of this is shown to correspond to the changes in the backscatter spectrum versus real frequency as computed using a Mie series expansion. The significant difference between the lossless and lossy dielectric-coated sphere cases is seen to be due to a modification of the phase velocities of surface waves, particularly the whispering gallery types, and the increased attenuation of the surface wave modes     

The nonsqueaky wheel

This paper presents a new approach, termed performance-based maintenance, can utilize past and ongoing equipment maintenance records to prioritize electrical distribution equipment with greater detail. The proposed scheme provides cost savings and useful in identifying equipment that can have a lesser level of future maintenance, or extended maintenance cycles. The integration of multiple inputs is required to minimize the risks associated with improper equipment prioritization. The savings can be redirected to areas such as predictive diagnostics, which can provide for greater improvements in reliability while also reducing the over all spend on maintenance.     

Study of the metal dusting behaviour of high‐temperature alloys

The corrosion phenomenon named metal dusting has been observed in many high‐temperature industrial plants. An experimental research programme is being carried out into the degradation resistance of wrought and cast commercial and development high‐temperature alloys in H₂/CO gas mixtures at temperatures of 550°C to 750°C. Emphasis is placed on very high carbon activities, consistent with the next generation of steam‐reforming and similar plants that are susceptible to metal dusting. The overall programme is concerned with the mechanisms of initiation and propagation of dusting and the sensitivity to damage of the more resistant alloys, as a function of environmental parameters. Initial tests have been carried out on a number of commercial alloys: Alloy 600, 693, 602CA, 601, 603 XL, 671, 617, 690 (wrought), and H46M (cast). The specimens were exposed to a gas mixture of high carbon activity at 650°C for a total of 1000 hours. Many of the alloys showed at least the initial stages of metal dusting. Preliminary analysis using electron microscopy revealed that initiation of metal dusting is influenced by microstructure, stress state and composition. In some cases, attack was enhanced at stress points, such as corners and edges. Sample holders were found to influence strongly the length of the initiation period for the onset of the corrosion phenomenon. The reaction layers in the alloy beneath areas of damage were analysed by EDX and EPMA. Mechanical characterisation of such areas has been carried out using nanoindentation methods. These early results are discussed in terms of the effectiveness of oxide scales in inhibiting the onset of damage and presence of impurities in the ceramic holder in initiating the onset of damage.     

Learning graphical models for stationary time series

Probabilistic graphical models can be extended to time series by considering probabilistic dependencies between entire time series. For stationary Gaussian time series, the graphical model semantics can be expressed naturally in the frequency domain, leading to interesting families of structured time series models that are complementary to families defined in the time domain. In this paper, we present an algorithm to learn the structure from data for directed graphical models for stationary Gaussian time series. We describe an algorithm for efficient forecasting for stationary Gaussian time series whose spectral densities factorize in a graphical model. We also explore the relationships between graphical model structure and sparsity, comparing and contrasting the notions of sparsity in the time domain and the frequency domain. Finally, we show how to make use of Mercer kernels in this setting, allowing our ideas to be extended to nonlinear models.     

On nested convolutional codes and their application to woven codes

Nested convolutional codes are a set of convolutional codes that is derived from a given generator matrix. The structural properties of nested convolutional codes and nested generator matrices are studied. A method to construct the set of all minimal (rational) generator matrices of a given convolutional code is presented. As an example, two different sets of nested convolutional codes are derived from two equivalent minimal generator matrices. The significant difference in their free-distance profiles emphasizes the importance of being careful when selecting the generator matrices that determine the nested convolutional codes. As an application of nested convolutional codes, woven codes with outer warp, and inner nested convolutional codes are considered. The free-distance profile of the inner generator matrix is shown to be an important design tool.     

Mobile IPv6 — Wegweiser in eine mobile Zukunft

Since mobile computing is getting more and more common, wireless technology is increasingly being used for Internet access and other IP-based communications. Some years ago, only a few people were using mobile phones to make telephone calls over GSM, whereas today you will hardly find anyone without his mobile companion in his pocket. In the future people will demand to get connected to the Internet by their IP-enabled smart-phones and PDAs always and anywhere. This article presents the upcoming Mobile IPv6 protocol, which will be the base for tomorrow’s worldwide IP-mobility. Mobile IPv6 will be widespread with the introduction of the Next-Generation Internet (IPv6).     

Ozonation of Cycloalkenes Dissolved in Ethanol

The ozonation of cyclooctene and cyclododecene in ethanol was studied at 278 K in a stirred reactor with a flat gas/liquid interface. The parallel reactions with ethanol in the gas and the liquid phase had to be accounted for. At high cyclooctene concentrations, ozone transfer into the liquid phase was enhanced by up to a factor of E = 325. Due to the high ozone solubility and the high enhancement factors, up to half of the mass transfer resistance was on the gas-side. The reaction rate constant k₂ is more than threefold higher for cyclooctene as compared to cyclododecene.