On the reflection of light from an inhomogeneous shell

The main contribution to the reflected field from a radially inhomogeneous spherical shell is determined. It is shown that it is much smaller in amplitude than the field reflected by a perfectly conducting sphere coated with the same type of radially inhomogeneous dielectric.     

Gain enhancement methods for printed circuit antennas through multiple superstrates

Reciprocity and a transmission line model are used to determine the radiation properties of printed circuit antennas (PCA's) in a multilayered material configuration. It is demonstrated that extremely high directive gain may result at any scan angle, with practical materials, if the thickness of the substrate and multiple superstrate layers is chosen properly. This model is also used to analyze the radiation characteristics of printed circuit antennas in inhomogeneous substrates.     

I Am What I See: How Avatar and Opponent Agent Body Size Affects Physical Activity Among Men Playing Exergames

This study examined how avatar body size (normal, obese) and opponent character body size (normal, obese) influenced physical activity while male participants played an exergame. Males operating normal weight avatars showed more physical activity than those using obese avatars. Perceived avatar and opponent character body‐size differences moderated the effect of avatar appearance on physical activity. Participants showed decreased physical activity when the opponent character was perceived as slightly more obese than their avatar. Participants also showed decreased physical activity when their avatar was perceived as more obese than the opponent character. We discuss theoretical implications and applications of using virtual characters to increase gamers' physical activity. These findings are also compared to an earlier study with an all‐female sample.     

On the prediction of internal particle morphology in suspension polymerization of vinyl chloride. Part I:: The effect of primary particle size distribution

The present study provides a comprehensive investigation on the determination of the primary particle size distribution in the suspension “powder” polymerization of vinyl chloride. The primary particle size distribution inside the polymerizing monomer droplets is determined by the solution of a population balance equation governing the nucleation, growth, and aggregation of the primary particles. The stability of the colloidal primary particles is expressed in terms of the electrostatic and steric stabilization forces. The primary particle stability model includes the effects of agitation, temperature, electrolyte as well as primary and secondary stabilizer concentrations. It also includes both diffusive and shear-induced particle destabilization mechanisms. The proposed stability model is shown to accurately describe existing experimental data on particle number, mean particle size and particle size distribution for both bulk and suspension vinyl chloride polymerizations. The primary particle population balance model can predict the critical monomer conversion at which massive particle aggregation occurs leading to the formation of a continuous network of primary polymer particles inside the polymerizing monomer droplets. A detailed investigation on the predicted critical monomer conversion is carried out including its dependence on the rate of agitation, temperature, electrolyte concentration, as well as the concentrations of the primary and secondary stabilizers.     

Part II: Dynamic evolution of the particle size distribution in particulate processes undergoing simultaneous particle nucleation, growth and aggregation

The present study provides a comprehensive investigation on the solution of the dynamic population balance equation (PBE) for particulate processes undergoing simultaneous particle nucleation, growth and aggregation. The general PBE was numerically solved in both the continuous and its equivalent discrete form using the orthogonal collocation on finite elements and the discretized PBE method, respectively. A detailed investigation on the effect of particle nucleation rate on the calculated particle size distribution (PSD) was carried out over a wide range of variation of dimensionless aggregation, nucleation and growth times. The performance (i.e., accuracy and stability) of the two numerical methods was assessed by a direct comparison of predicted PSDs and/or their respective moments to available analytical solutions. For combined aggregation and nucleation problems, the numerical error scaled with the product of the dimensionless aggregation and nucleation times. On the other hand, for combined growth and nucleation problems, the numerical error scaled only with the dimensionless growth time. For particulate systems with minimal particle growth, constant particle nucleation rate and Brownian aggregation, the total particle number approached a “steady-state” value characterized by the equilibrium of particle aggregation and nucleation rates. When the particle nucleation rate followed a pulse-like function, the PSD converged to a self-similar distribution after the end of particle nucleation. Moreover, for particulate systems exhibiting a constant particle nucleation rate and a Brownian-type particle aggregation kernel, an increase in the particle growth rate resulted in a decrease in the final total number of particles. On the other hand, for a constant particle nucleation rate and an electrostatically stabilized Brownian aggregation kernel, an increase in the particle growth rate can lead to an increase in the final total number of particles.     

Fatigue Behavior of Inconel 718 TIG Welds

Mechanical behavior of reference and TIG-welded Inconel 718 specimens was examined in the present work. Tensile, constant amplitude fatigue, and fracture toughness tests were performed in ambient temperature for both, reference and welded specimens. Microstructure revealed the presence of coarse and fine-grained heat-affected zones. It has been shown that without any post-weld heat treatment, welded specimens maintained their tensile strength properties while their ductility decreased by more than 40%. It was found that the welded specimens had lower fatigue life and this decrease was a function of the applied fatigue maximum stress. A 30% fatigue life decrease was noticed in the high cycle fatigue regime for the welded specimens while this decrease exceeded 50% in the low cycle fatigue regime. Cyclic stress-strain curves showed that Inconel 718 experiences a short period of hardening followed by softening for all fatigue lives. Cyclic fatigue response of welded specimens’ exhibited cyclically stable behavior. Finally, a marginal decrease was noticed in the Mode I fracture toughness of the welded specimens.     

Estimating reliability measures for highly-dependable Markovsystems, using balanced likelihood ratios

Over the past several years, importance sampling in conjunction with regenerative simulation has been presented as a promising method for estimating reliability measures in highly dependable Markov systems. Existing methods fail to provide benefits over crude Monte Carlo for analyzing systems that contain important component-redundancies. This paper presents refined importance-sampling techniques that are also based on the regenerative technique. The new methods use an importance-sampling plan that dynamically adjusts the transition probabilities of the embedded Markov chain by attempting to cancel terms of the likelihood ratio within each cycle. Additional improvements are induced by concentrating on events affecting the size of minimum system cuts. These methods have solid theoretical properties and work well in practice, as illustrated by several examples     

Monolithic waveguide filters using printed photonic-bandgapmaterials

A system of N dielectric layers imprinted with a transverse lattice of planar metallic scatterers and stacked monolithically along the longitudinal direction of a rectangular waveguide is examined in this paper. This monolithically constructed photonic crystal exhibits valuable filtering properties. The resulting optimized filters are inexpensive to fabricate because the building block (printed layer) is ideal for mass production. The complete filter contains no air gaps (monolithic) and can be modularly built up, or reconfigured, by simple stacking requiring no adhesives (modular). The filter response is designed using our analytical expressions and fast software, as well as using commercial software such as HFSS. A comparison of the two design methods shows that our approach is five orders of magnitude faster than HFSS and significantly reduces the memory requirements. Prototype measurements in the Ka-band show excellent agreement with predictions of our design method. Optimized designs displaying reduced size, extremely flat passbands (0.25 dB), and great isolation (-100 dB) are also presented     

The effect of the time and mode of application of gibberellic acid on the growth and yield of potato plants derived from true potato seed

The effect of the time and mode of treatment (single or repeated applications) of gibberellic acid (GA₃) on the growth and tuberisation of plants grown from true seed (TPS) of potato Chacasina F₁ was studied. Plant height, fresh and dry weight of stems and leaf dry weight increased in response to single or repeated GA₃ applications. Leaf colour was not affected by single applications of GA₃, whereas repeated applications caused a reduction in colour intensity. The numbers of secondary shoots and leaves per plant as well as total leaf area were largely unaffected by GA₃, although repeated applications from early in the growth cycle increased these parameters under conditions of decreasing photoperiod. When applied as a single dose during spring, GA₃ caused an increase in the number of tubers per plant, with a concomitant decrease in tuber dry matter content, irrespective of application date. In autumn the number of tubers per plant increased following single applications of GA₃ up to 50 days after transplantation, whereas tuber dry matter decreased. By contrast, repeated applications of GA₃ in both seasons increased tuber number only when initiated early in the growth cycle. The mean weight of tubers per plant was variably affected by GA₃ application, depending on the season, time and mode of application. It is suggested that the foliar application of GA₃ to plants from TPS at an early stage of vegetative development may be of value for seed tuber or micro‐tuber production, primarily by increasing the number of tubers produced per plant. Copyright © 2006 Society of Chemical Industry     

Autonomic cardiovascular neuropathy in Sj?gren's syndrome. A controlled study

OBJECTIVE: To test patients with primary Sj?gren's syndrome (SS) for evidence of autonomic neuropathy. METHODS: Thirty-two patients with primary SS and 22 age and sex matched healthy individuals were asked specific questions about symptoms suggestive of autonomic neuropathy, and were subjected to a battery of 5 cardiovascular tests: response of blood pressure to sustained hand grip, Valsalva maneuver, heart rate response to deep breathing, and heart rate and blood pressure response to standing up. The chi-squared test with Yates' correction and 95% confidence intervals were used for statistical analysis of the results. RESULTS: Sixteen patients (50%) had symptoms of autonomic neuropathy when specifically asked versus none of the controls (p < 0.0005). The frequency of abnormal responses to the tests was 68.8% in patients and 12.7% in controls (p < 0.0001). Severe autonomic cardiovascular neuropathy was found in 87.5% of the patients but in none of the healthy individuals (p < 0.0001). CONCLUSION: Our results suggest that autonomic neuropathy is a feature of a significant portion of the SS population, and such patients should have appropriate evaluation. Similarly, patients with unexplained autonomic neuropathy should be investigated for evidence of SS.