Designing monotonic low-pass filters—comparison of some methods and criteria

A New Approach Has Been Presented To Find Characteristic Functions Of A Certain Class Of Monotonic Low-Pass Filters Of Non-Maximally Flat Type. The Well-Known Legendre Filters, And The More Recently Introduced Class H Filters, Both Belonging To This Class, Are Derived As Special Cases Of The Application Of Least-Squares Approximation Technique By Optimizing The Asymptotic Loss. It Is Shown That Class H Filters Provide Higher Stopband Attenuation Than The Legendre Filters But Have Less Favourable Passband Magnitude Response. On The Other Hand, If The Minimization Of The Passband Loss Is At A Premium Then The Unconstrained Least-Squares Monotonic Approximants, Referred To As Lsm Filters, Yield The Best Results. Therefore, Among All Filters With Monotonic Magnitude Response, The Legendre Filters Have Neither Optimum Passband, Nor Optimum Stopband Performance, Though They Are Suitable For Some Applications.     

Moment-method analysis of volume dielectric scatterers. Four independent entire-domain solutions: Is entire-domain philosophy a luxury or necessity in the method of moments?

Four independent methods are presented for entire-domain (large-domain) moment-method analysis of lossy, inhomogeneous dielectric scatterers. They share two basic steps in solving volume integral equations: (1) the approximation of the scatterer geometry by large trilinear hexahedrons; and (2) the approximation of the unknown vector function in the hexahedrons by three-dimensional polynomials. The results are compared among themselves and with those obtained by subdomain (the only existing) methods, demonstrating great superiority of the entire-domain approach in solving three-dimensional scattering and interaction problems. © 1996 John Wiley & Sons, Inc.     

Analysis of coupled inset dielectric guides under LSE and LSMpolarization

The inset dielectric guide (IDG) represents an easy-to-fabricate alternative to the image line that is also less sensitive to loss radiation at discontinuities. Two IDG geometries were analyzed, the so-called deep and shallow IDG structures, operating in the LSE and LSM polarizations, respectively. The propagation constants of single and coupled symmetrical IDGs have been calculated as well as the coupling coefficients of coupled guides. The transverse resonance diffraction method with variational formulation was used. Measured values show very good agreement with predicted values for the propagation constants of coupled deep slot IDGs. The information is a prerequisite for the design of directional couplers in IDG     

Towards understanding the influence of porosity on mechanical and fracture behaviour of quasi-brittle materials: experiments and modelling

In this work, porosity-property relationships of quasi-brittle materials are explored through a combined experimental and numerical approach. In the experimental part, hemihyrate gypsum plaster powder (\(\hbox {CaSO}_{4}\cdot 1/2\hbox {H}_{2}\hbox {O}\)) and expanded spherical polystyrene beads (1.5–2.0 mm dia.) have been mixed to form a model material with controlled additions of porosity. The expanded polystyrene beads represent pores within the bulk due to their light weight and low strength compared with plaster. Varying the addition of infill allows the production of a material with different percentages of porosity: 0, 10, 20, 30 and 31 vol%. The size and location of these pores have been characterised by 3D X-ray computed tomography. Beams of the size of \(20 \times 20 \times 150\) mm were cast and loaded under four-point bending to obtain the mechanical characteristics of each porosity level. The elastic modulus and flexural strength are found to decrease with increased porosity. Fractography studies have been undertaken to identify the role of the pores on the fracture path. Based on the known porosity, a 3D model of each microstructure has been built and the deformation and fracture was computed using a lattice-based multi-scale finite element model. This model predicted similar trends as the experimental results and was able to quantify the fractured sites. The results from this model material experimental data and the lattice model predictions are discussed with respect to the role of porosity on the deformation and fracture of quasi-brittle materials.     

Microstructure and Toughness of Seeded Hot-Pressed Si3N4 Ceramics

Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam~(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.     

Synthesis and characterization of bionanoparticle—Silica composites and mesoporous silica with large pores

A sol-gel process has been developed to incorporate bionanoparticles, such as turnip yellow mosaic virus, cowpea mosaic virus, tobacco mosaic virus, and ferritin into silica, while maintaining the integrity and morphology of the particles. The structures of the resulting materials were characterized by transmission electron microscopy, small angle X-ray scattering, and N₂ adsorption-desorption analysis. The results show that the shape and surface morphology of the bionanoparticles are largely preserved after being embedded into silica. After removal of the bionanoparticles by calcination, mesoporous silica with monodisperse pores, having the shape and surface morphology of the bionanoparticles replicated inside the silica, was produced,. This study is expected to lead to both functional composite materials and mesoporous silica with structurally well-defined large pores. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Transport performance of an 80-Gb/s WDM regional area transparentring network utilizing directly modulated lasers

The transport performance of a regional area wavelength division multiplexing (WDM) transparent optical network is studied. We present excellent performance results (Q factors for all received signals greater than 10 with small power penalties) for a ring network based on application-optimized cost-effective optical layer components and fiber. The network consists of six network nodes, interconnected with 86.5-km spans of uncompensated negative dispersion fiber, resulting in a maximum transmission distance around the ring of 519 km, and it supports 32 directly modulated channels operating at 2.5 Gb/s (80-Gb/s network capacity). The novel design of the network nodes ensures great flexibility in terms of scalability and transparency, as well as great performance. To our knowledge, the capacity-length product of this transparent network, using cost-effective directly modulated lasers (DMLs) and no dispersion compensation, is the highest ever reported     

Effect of operating parameters on sulphur capture in a pressurized circulating fluidized bed combustor

Experiments are conducted to investigate the effect of system pressure, Ca/S ratio and primary air velocity on sulphur capture in a pressurized circulating fluidized bed (PCFB) combustor. The pressure inside the PCFB combustor is varied from 200 to 700 kPa. The Ca/S ratio is varied from 1.6 to 3.0. The primary air velocity ranges from 3 to 7 ms^?1. The bed temperature is maintained at 750°C. The sulphur capture increases with system pressure in the present range of experimental investigations. The sulphur capture also increases with Ca/S ratio up to a certain ratio and then shows a decreasing trend for the given operating conditions. A semi‐empirical model is developed for explaining the sulphur capture mechanism in the pressurized circulating fluidized bed combustor under batch combustion conditions. The experimental data are validated with the model predictions and a reasonable agreement has been observed. Copyright © 2002 John Wiley & Sons, Ltd.     

Fast ephemeral DNA damage upon BaP injection

Injection of high concentrations of benzo[a]pyrene (10-125 micrograms BaP/g body weight) into young frogs (Xenopus laevis), fish (Gambusia affinis) or tissue culture cells (L 5178 Y) in a state of logarithmic growth causes alterations in DNA. In frogs these alterations reach a maximum at 60-90 min after application, then they decrease and become undetectable after 3 h. Within 8-12 days after the single BaP dose, a new wave of DNA alterations can again be detected. Parallel measurements of mixed function oxygenases (MFO) showed no short term activity changes within the first day. There was, however, an increase of activity starting on the 8th day following injection in frogs, and lasting until day 14. DNA alterations have been assessed by two methods. One is a modification of the alkaline filter elution method of Kohn et al. (1976) and is believed to determine the number of events leading to single strand breaks at alkaline pH. The other method determines the number of S1 nuclease sensitive sites in highly purified native DNA. Both results were found to be highly correlated. The effect does not seem to be caused by an impurity, unless an unknown, very minor, and extraordinarily active component is present. The effect in frogs is linked to nutritional status. Frogs fed a carbohydrate-rich, protein-poor diet do not give the fast response. The fast effect cannot be blocked by application of Actinomycin, Cordycepin, and Chloramphenicol injected either 30 min before or simultaneously with the BaP. Benzo(e)pyrene, a non-tumorigenic isomer of BaP, does not cause any effects at similar doses.