Electromagnetic backscattering by corner reflectors

The Geometrical Theory of Diffraction (GTD), which supplements Geometric Optics (GO), and the Physical Theory of Diffraction (PTD), which supplements Physical Optics (PO), are used to predict the backscatter cross sections of dihedral corner reflectors which have right, obtuse, or acute included angles. These theories allow individual backscattering mechanisms of the dihedral corner reflectors to be identified and provide good agreement with experimental results in the azimuthal plane. The advantages and disadvantages of the geometrical and physical theories are discussed in terms of their accuracy, usefulness, and complexity. Numerous comparisons of analytical results with experimental data are presented. While physical optics alone is more accurate and more useful than geometrical optics alone, the combination of geometrical optics and geometrical diffraction seems to out perform physical optics and physical diffraction when compared with experimental data, especially for acute angle dihedral corner reflectors

Electromagnetic backscattering by corner reflectors

The analysis of the backscatter cross section of a dihedral corner reflector, using Geometrical Theory of Diffraction (GTD) and Physical Theory of Diffraction (PTD), is completed in the azimuthal plane, and very good agreement with experimental results is obtained. The advantages and limitations of the GTD and PTD techniques are discussed specifically for radar cross section applications. The utilization of GTD and PTD in oblique incidence diffraction from conducting targets is discussed. Results for equivalent current off-axis diffraction from the flat rectangular plate are presented using the equivalent currents of Knott, Senior, and Michaeli. The rectangular subdivision technique of Sikta, and its extension by Sunatara, alleviate some of the limitations of the equivalent techniques. As yet, neither technique can be used in bistatic scattering or for multiple scattering of a complex target

Electromagnetic scattering by impedance structures

The scattering of electromagnetic waves from impedance structures is investigated, and current work on antenna pattern calculation is presented. A general algorithm for determining radiation patterns from antennas mounted near or on polygonal plates is presented. These plates are assumed to be of a material which satisfies the Leontovich (or surface impedance) boundary condition. Calculated patterns including reflection and diffraction terms are presented for numerious geometries, and refinements are included for antennas mounted directly on impedance surfaces. For the case of a monopole mounted on a surface impedance ground plane, computed patterns are compared with experimental measurements. This work in antenna pattern prediction forms the basis of understanding of the complex scattering mechanisms from impedance surfaces. It provides the foundation for the analysis of backscattering patterns which, in general, are more problematic than calculation of antenna patterns. Further proposed study of related topics, including surface waves, corner diffractions, and multiple diffractions, is outlined

Electromagnetic backscattering by plates and disks

With the recent development of diffraction coefficients for imperfectly conducting half-planes, it has become possible to analyze a wide variety of problems for which the impedance surface boundary condition applies. This impedance boundary condition, while approximate, was utilized to extend the usefulness of the Uniform Geometrical Theory of Diffraction (UTD) beyond the perfectly conducting geometries. These half-plane diffraction coefficients are used to analyze patterns of an antenna in the presence of an imperfectly conducting flat polygonal plate. The Geometrical Theory of Diffraction (GTD) techniques were also used to investigate the backscattering from perfectly conducting plates. To further improve the soft polarization results for wide angles, a model for the creeping wave or circulating current on the edge of the disk was obtained and used to find an additional component of the backscattered field. The backscattering from a square plate was then analyzed using GTD. Backscattering in both the principal and off-principal planes was examined

Incubating females use dynamic risk assessment to evaluate the risk posed by different predators

Uncertainty poses a substantial problem for animals, making it is essential for individuals to anticipate changes in their environment to select suitable behavioral strategies. In nest-building species where parents care for dependent young, predation is a major cause of reproductive failure. However, because parents generally have inadequate information about nest predation risks, attaining information about predation hazards increases their likelihood of making informed, optimal decisions. Risk assessment should therefore be widespread, particularly in incubating parents of species that breed in cavities or closed nests, which have limited information about predator presence. This study experimentally investigated the dynamic risk assessment in incubating female brown thornbill (Acanthiza pusilla), a long-lived Australian passerine, which builds closed dome nests in dense vegetation. When the females were exposed to the calls of a nest predator, a predator of adults, and a nonpredatory species, they reacted most strongly to the predator of adults' calls, by looking out of the nest for longest. Females significantly increased their level of alertness on hearing calls of both predator species and maintained their higher level of alertness after the simulated predator presence ended. Females in nests with a high degree of visual cover, and therefore a larger information deficit, reacted more strongly to predator calls than females in more open nests. Moreover, poorly concealed nests had a higher probability of being predated. These results show that incubating female thornbills use dynamic risk assessment and base their response on who is at risk and the degree of information defici

Incubating females use dynamic risk assessment to evaluate the risk posed by different predators

Uncertainty poses a substantial problem for animals, making it is essential for individuals to anticipate changes in their environment to select suitable behavioral strategies. In nest-building species where parents care for dependent young, predation is a major cause of reproductive failure. However, because parents generally have inadequate information about nest predation risks, attaining information about predation hazards increases their likelihood of making informed, optimal decisions. Risk assessment should therefore be widespread, particularly in incubating parents of species that breed in cavities or closed nests, which have limited information about predator presence. This study experimentally investigated the dynamic risk assessment in incubating female brown thornbill (Acanthiza pusilla), a long-lived Australian passerine, which builds closed dome nests in dense vegetation. When the females were exposed to the calls of a nest predator, a predator of adults, and a nonpredatory species, they reacted most strongly to the predator of adults' calls, by looking out of the nest for longest. Females significantly increased their level of alertness on hearing calls of both predator species and maintained their higher level of alertness after the simulated predator presence ended. Females in nests with a high degree of visual cover, and therefore a larger information deficit, reacted more strongly to predator calls than females in more open nests. Moreover, poorly concealed nests had a higher probability of being predated. These results show that incubating female thornbills use dynamic risk assessment and base their response on who is at risk and the degree of information defici

Anti-infective surface coatings: design and therapeutic promise against device-associated infections

Patient safety and well-being are under increasing threat from hospital-acquired infections [1]. The root cause of a large number of these infections arises from microbial biofilms that colonise on surfaces of medical devices such as the millions of catheters, endotracheal tubes, and prosthetics implanted every year [2]. Biofilm infections are accompanied by increased resistance to antimicrobial therapy and immune clearance, severely limiting treatment options and leading to life-threatening disease [3,4]. Device-associated infections are caused by both bacteria and fungi and, while most studies have focused on single-species biofilms, biofilm-related infections are often polymicrobial [5–8]. Multi-species biofilms, particularly those involving bacterial and fungal pathogens, are more challenging to treat, likely as a consequence of their combined architecture, protective extracellular matrix, and potential synergism in protecting against antimicrobials and host immunity [9–11]. Among the fungi, Candida species are the most important biofilm pathogens [12,13] and the fourth leading cause of blood-stream infections in United States hospitals [7]. Fungal diseases remain difficult to diagnose, mortality rates remain high, and antifungal drug resistance continues to limit therapeutic options [14,15]. We are in desperate need of innovative strategies that target the mechanisms of pathogenesis of polymicrobial biofilms on medical devices. This is a grand challenge because it requires multidisciplinary collaboration and breakthrough research involving physical chemistry, materials science, and microbiology. Communication between these disciplines has not been common, but recent advances show greater convergence in the development of anti-infective devices. At this nexus, we outline the therapeutic promise of anti-infective coatings for medical devices and discuss pitfalls and strategies for overcoming them.Bryan R. Coad, Hans J. Griesser, Anton Y. Peleg, Ana Trave

RF switch positioner for communications satellite network

The RF switch positioner is a simple, lightweight, redundant positioning mechanism used to reconfigure the antenna beam on the INTELSAT VI satellite. It simultaneously rotates approximately 100 squareax waveguide switches through a full 360 deg. The RF switch positioner has been space qualified and has performed to expectations in conjunction with the feed networks in range testing

Advanced biopolymer-coated drug-releasing titania nanotubes (TNTs) implants with simultaneously enhanced osteoblast adhesion and antibacterial properties

Abstract not availableTushar Kumeria, Htwe Mon, Moom Sinn Aw, Karan Gulati, Abel Santos, Hans J. Griesser, Dusan Losi