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Objective: This study analyzed the causes of sphenoid sinus (SS) infection (SSI) following endoscopic transsphenoidal skull base surgery and determined appropriate treatment methods. Methods: This study included 31 cases of secondary SSI following the endoscopic transsphenoidal approach (ETSA; SSI group) and 246 cases without SSI (non‐SSI group). Data collected included post‐ETSA pathological results, types of artificial skull base reconstruction materials, and SS patency. For the SSI group, data included time from ETSA to symptom onset, endoscopic and imaging findings, intraoperative conditions during the second surgery, and changes in visual analog scale (VAS) scores. Results: The incidence of secondary SSI was 11.19%. In the SSI group, 26 patients (83.87%) reported headaches, and 24 (77.42%) had stenosis or closure of the SS ostium (SSO). The non‐SSI group reported no symptoms, and 236 patients (95.93%) had well‐opened SSOs. Centripetal hyperosteogeny (CHO) in the SS walls was observed in 20 patients (64.5%) in the SSI group. Absorbable materials were used in five cases (16.13%) and 215 cases (87.40%) in the SSI and non‐SSI groups, respectively, while non‐absorbable materials were used in 24 cases (77.42%) and 20 cases (8.13%), respectively. SSI risk was 9.42 times higher with non‐absorbable synthetic materials. VAS scores for SSI symptoms and Lund–Kennedy scores significantly decreased at 3 and 12 months post‐second surgery. Conclusion: Secondary SSI after ETSA can cause persistent symptoms. Non‐absorbable synthetic repair materials should be avoided to prevent secondary SSI. Extended sphenoidectomy and removal of artificial materials can lead to rapid resolution of SSI symptoms. Level of Evidence: 4. [ABSTRACT FROM AUTHOR]

Objective: The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD)scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation. Materials and Methods: GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC® bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques. Results: Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as “holes” in vertebrae. Conclusion: Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact.

Objective: The objective of the study was to evaluate the effect of artificial high- and low-density materials on Bone mineral density (BMD) scans in dual-energy X-ray absorptiometry (DXA) method and emergence of black-hole artifact through GATE Monte Carlo simulation. Materials and Methods: GATE Monte Carlo code was utilized to simulate the artifact encountered in clinical scans acquired by HOLOGIC® bone densitometer. Two simplified phantoms were designed. The first one was a rectangular box with six smaller cubes inside and the second one was a body torso. Materials of cubes were spine bone, polymethyl methacrylate (PMMA), barium sulfate suspension in water, stainless steel, titanium alloy, and gold. The torso phantom contained objects of 5 vertebrae, bowel and 3 small spherical objects near the surface of the torso as piercing objects on the abdominal wall, each overlying the vertebrae. Using 100 and 140 kVp, spectral X-rays were generated to simulate DXA. For both phantoms, two simulations were carried out. The pair of projections acquired for each phantom were then subtracted and analyzed by curve fitting techniques. Results: Except for spine bone, in which radio-opacity decreases with increasing spectral X-ray energy (from 100 to 140 kVp), other squares exhibit little changes over different energies. PMMA shows consistently very low radio-opacity. Four other materials (barium sulfate in water, stainless steel alloy, titanium alloy, and gold), all attenuate the X-ray photons substantially. Except for spine bone, other materials are barely noticeable in pairwise subtracted images. In torso phantom, piercing objects are visualized as "holes" in vertebrae. Conclusion: Both artificial high- and low-density materials, compared to bone, are eliminated during the subtraction of dual-energy X-ray profiles and therefore, can create black-hole artifact. [ABSTRACT FROM AUTHOR]

The historical imitative crafts discussed in this study, such as scagliola, Coade stone, marbling and graining, were unique and original; their use was promoted and articulated between the end of the sixteenth and the nineteenth century. The conservation of imitative crafts may be compromised without a nuanced and specific approach. Conserving inventions of the past presents unique challenges since the mechanism of deterioration of artificial and natural materials intrinsically differ; the decay of natural stone or marble is different from that of scagliola. Current decision-making often aimed at increasing authenticity through retaining the ageing quality of the original fabric, may paradoxically devaluate the heritage significance if the original imitative intentions are not followed. This work aims to set a theoretical foundation upon which a code of practice could be developed to prevent further cultural heritage loss. The fundamental difference between artificial materials and imitative surfaces should inform guidelines for conservation policy. The skills of imitative crafts should be protected to retain their cultural significance. [ABSTRACT FROM AUTHOR]

Millimeter-wave bands (around 28, 38, 60, and 73 GHz) are anticipated to play a decisive role in the hosting of future wireless systems. The necessity of smart antennas to adaptively meet the requirements of the wireless links calls for new pattern reconfiguration antennas with beam-steering and/or beam-shaping capabilities. This paper reviews the latest research contributions on pattern reconfigurable antennas at mm-Wave frequencies, proposing an original classification according to the reconfiguration technique and technology. The analyzed systems are divided into two main groups: Reconfigurable and non-reconfigurable feeding antennas. Phased-arrays antennas are the main component of the first category, whereas other reconfigurable means such as the use of metasurfaces or advance materials like liquid crystal or graphene form the second group, devoted to non-reconfigurable feeding antennas. Furthermore, some insights and theoretical background are provided to help the reader understand and appreciate the uniqueness of every solution. Similarly, the beam-scanning and beam-shaping performance of some of the discussed works is analyzed. Finally, some instructive remarks and open research challenges are discussed, with the aim of providing some guidelines for potential new works on the field.

The design of modular, passive, and static artificial metasurfaces to be used as electromagnetic skins (EMSs) of buildings for improving the coverage in urban millimeter-wave communication scenarios is addressed. Toward this end, an ad hoc design strategy is presented to determine optimal tradeoff implementation solutions that assure a suitable coverage of the areas of interest, where the signal from the base station is too weak, with the minimum complexity. More specifically, the admissible surface in the building facade is first partitioned into tiles that are the minimum-size elements of the artificial coating (i.e., the building block of an EMS). Then, the search for the optimal EMS layout (i.e., the minimum number and the positions of the tiles to be installed) is carried out with a binary multiobjective optimization method. Representative numerical results are reported and discussed to point out the features and the potentialities of the EMS solution in the smart electromagnetic environment (SEME) and the effectiveness of the proposed design method. [ABSTRACT FROM AUTHOR]

A new self-oscillating circularly polarized active integrated antenna (CPAIA) featuring boosted dc-to-RF conversion efficiency is proposed and demonstrated in this letter. The conversion efficiency, 40% better than the second best design in the literature, is achieved by innovative integration of a CP exciter with a pair of anti-symmetrically arranged parasitic radiators. The CP exciter is a linearly polarized self-oscillating active dipole antenna consisting of zeroth-order resonators and a crosscoupled pair oscillator. In addition to oscillate and radiate a linearly polarized electrical field into space, it is responsible for coupling half of the oscillating power into the pair of parasitic radiators to excite another linearly polarized electric field spatially and temporally orthogonal to the original one for CP operation. The proposed CPAIA is fabricated and tested at 879 MHz, and is compared with the state-of-the-arts in the literature. Good agreement between the simulated and measured results validates the design concept, and the performance summary table highlights the advantages of the proposed design. [ABSTRACT FROM AUTHOR]

Objective:  To summarize experience in the treatment of pentalogy of Cantrell (POC) in our hospital and explore the effect of artificial materials in repairing sternal defects.Materials and Methods:  A retrospective analysis was performed on treatment of five children with POC treated by using the Gore-Tex patch and titanium mesh in the Department of Cardio-Thoracic Surgery, Children's Hospital of Chongqing Medical University, from January 2010 to January 2019.Results:  The concurrent conditions included double outlet of right ventricle (n = 2), ventricular septal defect (VSD) and atrial septal defect (ASD) (n = 1), VSD and ASD and patent ductus arteriosus (n = 1), and VSD and left ventricular diverticulum (n = 1) in five cases with POC. Color Doppler echocardiography and computed tomography (CT) + three-dimensional (3D) reconstruction of the thorax and abdomen were performed preoperatively. The cardiac malformation was corrected according to color Doppler echocardiography, and a Gore-Tex patch was used to repair the pericardial defect. Titanium mesh was made according to CT 3D reconstruction with a 3D printing mold to repair sternal defects. All patients underwent a one-stage operation, all hearts were eventually repositioned, no deaths occurred after the operation, and follow-up was performed for 6 months to 2 years. The patients recovered well, and the exterior thorax was normal.Conclusion:  The diagnosis of POC is not difficult. The priority of surgical treatment for POC is to obtain satisfactory corrections of cardiac malformation. The repair of the pericardial defect with the Gore-Tex patch and the sternal defect with the titanium mesh can make the heart return to the mediastinum, reduce the pressure on the heart, reduce the surgical trauma, reduce the difficulty of repairing the sternal defect, and optimally restore the exterior thorax. [ABSTRACT FROM AUTHOR]

This paper examines the influence of authentic materials on the motivation of the Faculty of Social Sciences, Kuwait University. The target population is male and female students of two intermediate levels at the Faculty of Social Sciences, Kuwait University. All students received both artificial and authentic materials. Data from two observation sheets as well as self-report questionnaires showed that on-task behavior and observed motivation increased when authentic materials were used, but selfreported motivation increased for all classes only in the last two to three weeks of the experiment. On the other hand, students believe that artificial materials are more enjoyable than authentic materials. The result of this experiment generally found that artificial materials are more interesting than authentic materials. [ABSTRACT FROM AUTHOR]

In order to explore the mechanical properties of rock with deep in-situ stress under explosive impact, cemented sand material (artificial material) instead of rock was used to carry out impact dynamics test under the condition of confining pressure. The experimental results show that the stress-strain curve of cemented sand specimens tested by triaxial impact compression changes significantly compared with those tested by uniaxial impact compression. The dynamic failure mode of cemented sand specimens placed under confining pressure constraints is one of axial tensile failure, while the dynamic compressive growth factor, peak strain, dynamic elastic modulus, and specific energy absorption of cemented sand specimens all have the characteristics correlated with confining pressure. The research results in this study can be as an important basis for the mechanism analysis of rock breaking by blasting in deep rock mass. [ABSTRACT FROM AUTHOR]

A bi-layered twisted F-shaped chiral metamaterial is proposed in this work to realize efficient cross-polarizer convertor (CPC). Reported CPC design exhibited high optical activity owing to the cross-coupling between the applied electric field and the induced electric/magnetic field. The mechanism of CPC is described through the surface current distribution. The proposed design is fabricated and tested experimentally to verify the CPC functionality. The obtained experimental results are in good agreement with numerical simulation results. [ABSTRACT FROM AUTHOR]

Endothelial keratoplasty is the main surgical procedure for treating corneal endothelial dysfunction (CED), which is limited by the global shortage of donor corneas. Herein, we developed and evaluated the modified thermoplastic polyurethane (M-TPU) films with gelatin-glycidyl methacrylate to replace the corneal endothelial function and maintain corneal transparency. The films displayed comparable light transmission characteristics with normal corneas and clinically favorable mechanical properties for surgical manipulation. After surface modification, the hydrophilicity and biocompatibility of M-TPU films were significantly improved. In the rabbit CED model, the M-TPU implants exhibited firm adhesion to the exposed stromal surface. The rabbit corneal transparency and thickness could be restored completely within 1 week of M-TPU film implantation. There was no significant inflammatory reaction and immune rejection during the follow-up of 1 month. Proteomic analysis suggested that the complement inhibition, the increase of mineral absorption, and the decrease of P53 apoptosis signaling pathway and lysine degradation might be beneficial in maintaining the corneal transparency. Overall, our study demonstrated the potential of M-TPU films as artificial implants for the replacement of corneal endothelial function to restore corneal thickness and transparency.

Inverse design procedures aim at determining optimal parameters for a given device in order to satisfy assigned specifications. In this contribution, the design of optimal EBG waveguides through inverse problems tools is addressed. In particular, an inversion tool based on the so called ‘scattering matrices’ is proposed and assessed to optimize the guiding effect for straight and bent waveguides.

This paper discusses several efforts made to study and investigate soft rocks, as well as their physico-mechanical characteristics recognized up to now, the problems in their sampling and testing, and the possibility of its reproduction through artificially made soft rocks. The problems in utilizing current and widespread classification systems to some types of weak rocks are also discussed, as well as other problems related to them. Some examples of engineering works in soft rock or in soft ground are added, with emphasis on their types of problems and solutions.

By ingeniously integrating a pair of zeroth-order resonators (ZORs) with a cross-coupled pair, for the first time, a novel zeroth-order self-oscillating active integrated antenna (AIA) is developed. Unlike the conventional feedback oscillating AIA, the new configuration is realized by, respectively, inserting a ZOR into each of the feedback paths of the cross-coupled pair to satisfy the Barkhausen criterion, and hence stabilize the oscillation. A self-oscillating AIA operates at the UHF radio frequency identification (RFID) band was demonstrated as a proof of concept. Benefitting from the infinite-wavelength property, the embedded ZORs are electrically large and capable of providing efficient power radiation into space. The oscillation parameters, meanwhile, remain good, thanks to the inherent high-quality factor property of metamaterial resonators. Without relying on ground radiation, the new design achieves good radiation and oscillation performances at the same time, hence adding extra flexibility on shaping the radiation pattern. According to the experimental results, the developed AIA, oscillating at 0.92 GHz, features a high dc-to-RF conversion efficiency of 52%, a moderate effective isotropic power of 8.9 dBm, and a low phase noise of −124.7 dBc/Hz at a 1 MHz offset from the carrier frequency. The design principle and experimental demonstration are thoroughly discussed. [ABSTRACT FROM PUBLISHER]

Spheroidal wave functions depend on a parameter $c$ . Their behavior with respect to changes of sign of $c$ is investigated, and explicit formulas are provided. Sample applications of the resulting symmetry rules are provided for some electromagnetic scattering problems. [ABSTRACT FROM AUTHOR]

Can artificial materials be developed that rival nature's ability to self-assemble and self-replicate? Zorana Zeravcic, lecturer and researcher at the École Supérieure de Physique et de Chimie Industrielles Paris Sciences et Lettres Research University in Paris, outlines investigations on the subject being carried out by her department and by counterparts at Harvard University in the US. Drawing on methodologies and knowledge from across the sciences, their simulations have yielded previously unenvisioned complex functionalities that could transform the way we build. [ABSTRACT FROM AUTHOR]

Urban bird dwellers survive and reproduce in highly urbanized ecosystems. Some individuals adjust to these novel conditions by changing natural nesting materials for artificial materials, thus making nests more conspicuous in the environment. The consequences of using artificial materials for nesting remain poorly understood, especially from a nest-predator perspective. We studied if exposed artificial materials on bird nests affect the daily survival rate in a common dweller species, the clay-colored thrush (Turdus grayi). We used previously collected nests with a different area of exposed artificial materials and placed them with clay eggs on the main campus of the Universidad de Costa Rica. During 12 days of the reproductive season, we monitored the nests using trap cameras located in front of each nest. We found that nest survival decreased as the proportion of exposed artificial materials increased in the nest and, unexpectedly, that the principal predators were conspecifics. Thus, artificial materials used in the outer layer of nests make them more susceptible to predation. The use of artificial materials likely reduce reproductive success and population size in urban clay-colored thrush, but further field experiments measuring the effect of waste in birds' nests on the reproductive success of urban birds are needed. [Display omitted] • Exposed human trash used for nesting reduce nest daily survival rate in birds. • Synthetic materials used for nesting make nests more conspicuous in the environment. • Conspecifics (clay-colored thrushes) results the principal nest predators. • Human waste could produce a critical effect on urban wildlife birds reproduction. [ABSTRACT FROM AUTHOR]

This paper presents stable magnetic-field and electric-field integral equation formulations for exterior electromagnetic scattering by either penetrable or perfectly conducting closed bodies of general shape. The development relies on an extension of the conventional reciprocity theorem allowing the fields produced by some combination of sources in one environment to be connected with the fields generated by another combination of sources in a different environment. By the use of lossy metamaterials, the internal-resonance problem inherent to the original versions is eliminated, and thus the new formulations are amenable to a unique, highly accurate, and well-conditioned solution. [ABSTRACT FROM PUBLISHER]

A self-oscillating active integrated antenna with very high dc-to-radio frequency (RF) conversion efficiency is proposed and validated with the aid of metamaterial resonators. The key innovation is the new integration scheme which allows an independent control of the resonators used in the feedback oscillator and the radiating element in the integrated antenna. The metamaterial resonator, featuring a high quality factor for good oscillation performances, is applied to excite the dipole-mode ground radiation with good radiation efficiency at the same time. The design principle is introduced; the circuit and antenna parameters including the loop gain, oscillation output power, phase noise, effective isotropic radiated power, and radiation patterns are investigated in detail. Its application to multicarrier RF identification systems as a low-cost continuous-wave source is supported by quantitative measurement results. [ABSTRACT FROM AUTHOR]

Two kinds of surface-wave waveguide (SWG) topologies are proposed in this paper with the objective to achieve the property of supporting both transverse magnetic (TM) and transverse electric (TE) modes with the same phase velocity. The first type is composed of two frequency-selective surfaces (FSSs) as layers whose dominant modes are TM mode and TE mode, respectively. For illustrationC the combination of loop-type FSS and wire-grid-type FSS is analyzed and its dispersion characteristics are examined as well. The second class also consists of two layers. For the top layer, there are gaps in one direction and continuous conducting strips in the orthogonal direction. The bottom layer is created from a 90° rotation of the top layer. As a particular illustration, a modified bow-tie-like SWG structure is investigated. The simulated results show that the two proposed SWG structures exhibit the property of supporting both TM mode and TE mode with the same phase velocity over a broad bandwidth. In addition, the effects of lattice types on dispersion diagrams are discussed in this paper. Near field measurements are also carried out to validate the simulations and good agreements are achieved. [ABSTRACT FROM AUTHOR]

The microwave concept of miniaturization of a rectangular patch antenna using two-layer metal-dielectric composite substrate with a large value in the real part of the effective relative permittivity is developed. Each layer is a metamaterial slab in the form of a parallelepiped dielectric matrix with periodically embedded metallic wires. The proposed idea is validated by numerical simulations for sample rectangular patch antennas. The comparative analysis of the simulation results is made at the frequencies of approximately 15 GHz. [ABSTRACT FROM AUTHOR]

The artificial materials for bone implant applications are gaining more importance in the recent years. The series titania‐chitosan‐chondroitin 4–sulphate nanocomposites of three different concentrations (2:1:x, where x ‐ 0.125, 0.25, 0.5) have been synthesised by in situ sol–gel method and characterised by various techniques. The particle size of the nanocomposites ranges from 30–50 nm. The bioactivity, swelling nature, and the antimicrobial nature of the nanocomposites were investigated. The swelling ability and bioactivity of the composites is significantly greater and they possess high zone of inhibition against the microorganisms such as Staphylococcus aureus and Escherichia coli. The cell viability of the nanocomposites were evaluated by using MG‐63 and observed the composites possess high cell viability at low concentration. The excellent bioactivity and biocompatibility makes these nanocomposites a promising biomaterial for bone implant applications. [ABSTRACT FROM AUTHOR]

The scattering from a rectangular metal sheet is altered by patterning the surface with hard and soft anisotropic impedance surfaces. A plane wave incident normally to an edge of a metal rectangle will have maximum backward scattering in the direction of the source for both transverse magnetic (TM) and transverse electric (TE) polarizations. This scattering lobe is manipulated by patterning the metal sheet in two sections. A hard surface is applied to the incident region which reflects neither TM nor TE waves from the front edge. Similarly, a soft surface prevents reflections of both polarizations from the back edge. The surfaces are patterned with an angled boundary, so that surface waves and incident radiation are scattered at an angle instead of backward. Unit cells are designed and analyzed for both regions for operation centered at 15 GHz. A surface is fabricated and measured, and the scattering alteration effect is achieved over a large bandwidth for each polarization. Curved and zigzag geometries are also discussed. [ABSTRACT FROM PUBLISHER]

We examined the settlement preferences of leeches by analysing colonization patterns on artificial substrates. The intention was to check whether the type of material, texture and size of artificial substrates would influence the abundance of leeches. To test substrate type preferences, we used the following nine artificial substrates: polyester, polycarbonate, aluminium, glass, rubber, steel, polyethylene, ceramics and polypropylene. In addition, substrates of different textures (structural vs. smooth) and sizes (900, 400, 100 cm) were used. We found that rubber, polyethylene and aluminium were most frequently chosen by the leeches. Surface structure and size of the objects were other factors which determined substrate selection by these organisms. Leeches more readily inhabited rough surfaces and the surfaces of smaller-sized objects. The species composition of leech assemblages on analysed artificial substrates was dominated by predatory taxa of the genus Erpobdella and Helobdella. [ABSTRACT FROM AUTHOR]

Metamaterials have been considered for their potential to improve the radiation characteristics of sources. A novel geometry consisting of a semioblate spheroidal cavity containing two layers, one made of DPS and the other made of DNG metamaterial, and built underneath an aperture in infinite metallic plane is considered. An exact analytical solution is obtained and its numerical evaluation demonstrates a significant improvement of the directive radiation of a dipole source, with the appropriate combination of the ordinary double positive (DPS) and DNG layers. [ABSTRACT FROM PUBLISHER]

A tensor impedance surface waveguide is built using anisotropic unit cells. The waveguide can propagate a confined waveguide mode along its axis while waves incident to the guide at an orthogonal direction pass through as if the waveguides were not present. Both straight and curved implementations are demonstrated. Surface waves incident at an angle to the waveguide show reflection and refraction at the impedance interface. A theoretical model for tensor impedance surface waveguides is generalized to include dispersive unit cells and bending loss around curves. Dispersion results for modes propagating in the waveguide show agreement between the theory, simulation, and experimental measurements. A curved waveguide is also constructed which guides surface waves around a curve and is transparent to surface waves incident at an orthogonal angle. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the reflection behavior of electromagnetic waves incident on an interface between an isotropic medium and a general electric–magnetic uniaxial lossy medium. We analyze this interface by applying the general Soft-Hard/DB (SH/DB) boundary conditions and discuss its response for some particular cases as well. The propagation of both homogeneous and inhomogeneous waves in a uniaxial lossy medium is discussed. It is found that for low losses the uniaxial medium under consideration is very suitable, while for higher losses it decreases its appeal for the realization of the SH/DB medium. The results obtained in the lossy case are compared with those of the lossless one, presented in the literature. Many metamaterials proposed can be homogenized as electric–magnetic uniaxial media. We investigate their characteristics and try to understand their limitations due to the presence of losses. [ABSTRACT FROM PUBLISHER]

A unit-cell design for highly anisotropic impedance surfaces is simulated and experimentally demonstrated. The unit cell consists of a grounded dielectric substrate with a metal patch and plated metal via. The design has a ring of metal removed from the patch so that the resonant effect of the via is reduced. The reduced resonance prevents backward-wave modes which are difficult to excite experimentally. On grounded dielectric substrates, the transverse-magnetic mode is fundamental and the transverse-electric (TE) mode is bound above a cutoff frequency. It is shown that highly anisotropic surface impedance can only be achieved below the TE cutoff frequency. The proposed unit cell is constructed using printed-circuit-board fabrication technology, and the result is a unit cell that obtains highly anisotropic impedance over a broader frequency range than traditional patch or mushroom unit cells. [ABSTRACT FROM PUBLISHER]

Miniaturized low-profile monopole antennas loaded by metamaterial (MTM) structures are presented. The antenna is loaded by zeroth-order resonator (ZOR) and complimentary split-ring resonator (CSSR) units, resonating over three frequency bands so that they can be tuned by changing the geometrical parameters of the MTM structures. Surface current distribution and equivalent circuit models are provided to describe the principle of operation. The experimental results are presented to validate the numerical results. Showing the monopole-shape radiation pattern characteristics at all resonant frequencies, the proposed MTM antennas are suitable for vehicular wireless applications. [ABSTRACT FROM PUBLISHER]

A surface wave beam shifter is designed using ringmushroom unit cells. The unit cell consists of a rectangular ring that surrounds an interior patch and plated via. The unit cell is anisotropic, and surface waves propagate with different directions of phase velocity and power flow. Two adjacent regions are designed such that the shift direction in each region is mirrored. The result is that an incident beam is split apart, and power does not radiate in the original direction of the beam. It is shown that an object placed in line with a source scatters surface waves in multiple directions from the object. By using a beam-splitting surface, the incident beam avoids the object, and scattering is significantly reduced. When the wave is incident in series with the two beam shifters, the surface shifts the wave in one direction followed by a shift in the opposite direction. [ABSTRACT FROM AUTHOR]

We investigate the effect of microwave-induced breakdown on the frequency responses of a class of metamaterials composed of planar sub-wavelength periodic structures. When breakdown occurs in such a structure, its frequency response changes based on the nature of the plasma created within its unit cell. We examine how the frequency responses of such periodic structures change as a result of creation of microwave-induced discharges within their unit cells. To do this, we examine single-layer metasurfaces composed of miniature LC resonators arranged in a 2-D periodic lattice. These metasurfaces are engineered to be opaque at microwave frequencies when operated at low power levels but can be made transparent if a localized discharge is created within the LC resonators. By measuring their transmission and reflection coefficients under high-power excitation in different conditions, the impact of breakdown on the frequency responses of these devices is determined. Several prototypes of such structures are examined both theoretically and experimentally. It is demonstrated that when breakdown occurs in air and at atmospheric pressure levels, the responses of such periodic structures can be predicted with a reasonable degree of accuracy. Additionally, when the unit cell of the metasurface is composed of two different resonators, breakdown is always observed to occur in both resonators despite their different topologies and local field enhancement factors. In such structures, the discharge in one resonator appears to be mediated by the one in the other. [ABSTRACT FROM PUBLISHER]

This preliminary study sets out to examine the extent to which authentic materials affect Japanese university students' classroom motivation, seeking an effective way to teach mixedlevel language classes at universities. The motivation questionnaires consisting of eight motivation items as quantitative data and journal entries and learners' comments in semistructured interviews as qualitative data were collected and analyzed. The results of null hypothesis tests on the questionnaires indicate that authentic materials had a significantly more positive effect on freshmen's self-reported motivation than artificial textbook materials, but not on second-year and fourth-year students'. The study also explores the relationship between enjoyableness and meaningfulness of teaching materials to seek the most effective way of using authentic materials, and discusses the effects of other possible factors such as activities and topics. The conclusion suggests that appropriate use of authentic materials, especially enjoyable ones, can be helpful for university teachers of relatively larger classes of freshmen with mixed proficiency levels to raise their L2 motivation. The challenges of conducting this research and suggestions about future studies are also discussed. [ABSTRACT FROM AUTHOR]

A surface waveguide structure is studied using a theoretical model and simulated using Ansoft HFSS. A tensor impedance surface is surrounded by two lower impedance surfaces on a plane. Surface waves are guided losslessly within the inner region as long as it has higher impedance than the outer region. A theoretical model is proposed which predicts the dispersion relation of the waveguide using a ray optics method. Our tensor impedance surface theory can also predict the dispersion of scalar impedance surfaces. The theory and simulation show agreement for scalar and tensor impedance surfaces. Two applications of tensor impedance surface waveguides are presented. [ABSTRACT FROM PUBLISHER]

We present the design of a flat lens, made by a conventional material and an epsilon near-zero metamaterial, to plug up the aperture of a short horn antenna, in order to achieve radiation performances similar to the ones of the corresponding optimum horn over a broad frequency range. Lens operation is based on the phase-compensation concept: phase-fronts of the field propagating along the short flare of the horn propagate with different phase velocities in the two lens materials, resulting in an uniform phase distribution on the aperture. Starting from the theoretical study of the transmission properties of a bulk epsilon near-zero slab, we derive the analytical formulas for the design of the flat lens and validate them through full-wave numerical simulations. Then, a realistic version of the lens, realized with a wire-medium and exhibiting a near-zero real part of the effective permittivity in the frequency range of interest, is presented. Considering two examples working in the C-band, we show that the lens can be designed for both conical and pyramidal horn antennas. In both cases, the length of the horns is half the one of the corresponding optimum versions, while the obtained radiation performances are similar to those of the optimum horns over a broad frequency band. This result may open the door to several interesting applications in satellite and radar systems. [ABSTRACT FROM PUBLISHER]

This study proposes an innovative device called “Hybrid-Superlens Hyperlens” with superresolution imaging ability and confirms it by using simulation. This device consists of two multilayered metal-dielectric anisotropic metamaterials: the upper planar superlens and the lower cylindrical hyperlens with different signs in their dielectric tensors and different isofrequency dispersion curves. In our simulation, 100-nm center-to-center resolution is obtained by using an incident wavelength of 405 nm, which is smaller than the optical diffraction limit. [ABSTRACT FROM PUBLISHER]

We present an equivalent X-shaped lumped circuit network to be interposed in the transmission line (TL) modelling reflection and transmission through a recently proposed metalayer in planar technology. The metalayer consists of arrayed pairs of planar conductors that support two main resonant modes, corresponding to either a symmetric or an antisymmetric current distribution in the pairs. The antisymmetric mode is associated with artificial magnetism. We show that reflection and transmission features of a metalayer are accurately predicted by this simple but effective TL model. We also make a clear distinction for the first time between transmission peaks and resonance frequencies, and their relations are investigated in detail. This paper clearly defines the concept of magnetic resonance and identifies the analytical conditions corresponding to total reflection and transmission through a metalayer made of pairs of conductors supporting symmetric and antisymmetric modes. [ABSTRACT FROM PUBLISHER]

Analysis of a printed-circuit tensor impedance surface (PCTIS) is presented. The surface consists of a periodic, subwavelength-patterned metallic cladding printed over a grounded dielectric substrate. First, the dispersion equation for an idealized tensor impedance boundary condition is derived by expressing the field in terms of TE and TM waves. A similar method is then used to find the dispersion equation of the PCTIS consisting of a tensor sheet impedance, which models the metallic cladding, over a grounded dielectric substrate. In addition, a method for extracting the tensor sheet impedance of a periodic, metallic cladding printed over a grounded dielectric substrate, is reported. It involves performing two normal-incidence scattering simulations using a full-wave electromagnetic solver. The method is strictly valid when the ground plane is sufficiently far from the metallic cladding to avoid evanescent-wave interactions. By combining the tensor sheet extraction method with the dispersion equation, the full dispersion characteristics of the PCTIS are analytically predicted in the homogenous limit. The results are verified through full-wave eigenmode simulations. [ABSTRACT FROM PUBLISHER]

We have developed a method for controlling electromagnetic surface wave propagation and radiation from complex metallic shapes. The object is covered with an artificial impedance surface that is implemented as an array of sub-wavelength metallic patches on a grounded dielectric substrate. We pattern the effective impedance over the surface by varying the size of the metallic patches. Using a holographic technique, we design the surface to scatter a known input wave into a desired output wave. Furthermore, by varying the shape of the patches we can create anisotropic surfaces with tensor impedance properties that provide control over polarization. As an example, we demonstrate a tensor impedance surface that produces circularly polarized radiation from a linearly polarized source. [ABSTRACT FROM PUBLISHER]