Transmission-Line Analysis of Epsilon-Near-Zero (ENZ)-Filled Narrow Channels

Following our recent interest in metamaterial-based devices supporting resonant tunneling, energy squeezing and supercoupling through narrow waveguide channels and bends, here we analyze the fundamental physical mechanisms behind this phenomenon using a transmission-line model. These theoretical findings extend our theory, allowing us to take fully into account frequency dispersion and losses and revealing the substantial differences between this unique tunneling phenomenon and higher-frequency Fabry-Perot resonances. Moreover, they represent the foundations for other possibilities to realize tunneling through arbitrary waveguide bends, both in E and H planes of polarization, waveguide connections and sharp abruptions and to obtain analogous effects with geometries arguably simpler to realize.Comment: 35 pages, 9 figure

Low sidelobe level low-cost earth station antennas for the 12 GHz broadcasting satellite service

An experimental investigation of the performance of 1.22 m and 1.83 m diameter paraboloid antennas with an f/D ratio of 0.38 and using a feed developed by Kumar is reported. It is found that sidelobes below 30 dB can be obtained only if the paraboloids are relatively free of surface errors. A theoretical analysis of clam shell distortion shows that this is a limiting factor in achieving low sidelobe levels with many commercially available low cost paraboloids. The use of absorbing pads and small reflecting plates for sidelobe reduction is also considered

Comparison of Gaussian process modeling software

Gaussian process fitting, or kriging, is often used to create a model from a set of data. Many available software packages do this, but we show that very different results can be obtained from different packages even when using the same data and model. We describe the parameterization, features, and optimization used by eight different fitting packages that run on four different platforms. We then compare these eight packages using various data functions and data sets, revealing that there are stark differences between the packages. In addition to comparing the prediction accuracy, the predictive variance--which is important for evaluating precision of predictions and is often used in stopping criteria--is also evaluated

British American Tobacco and the "insidious impact of illicit trade'' in cigarettes across Africa

Objectives: To provide an overview of the complicity of British American Tobacco (BAT) in the illicit trade of cigarettes across the African continent in terms of rationale, supply routes and scale.Methods: Analysis of internal BAT documents and industry publications.Results: BAT has relied on illegal channels to supply markets across Africa since the 1980s. Available documents suggest smuggling has been an important component of BAT's market entry strategy in order to gain leverage in negotiating with governments for tax concessions, compete with other transnational tobacco companies, circumvent local import restrictions and unstable political and economic conditions and gain a market presence. BAT worked through distributors and local agents to exploit weak government capacity to gain substantial market share in major countries.Conclusions: Documents demonstrate that the complicity of BAT in cigarette smuggling extends to Africa, which includes many of the poorest countries in the world. This is in direct conflict with offers by the company to contribute to stronger international cooperation to tackle the illicit tobacco trade.</p

Coaxial prime focus feeds for paraboloidal reflectors

A TE11 - TM11 dual mode coaxial feed for use in prime focus paraboloidal antenna systems is investigated. The scattering matrix parameters of the internal bifurcation junction was determined by the residue calculus technique. The scattering parameters and radiation fields of the aperture were found from the Weinstein solution. The optimum modeing ratio for minimum cross-polarization was determined along with the corresponding optimum feed dimensions. A peak cross-polarization level of -58 dB is predicted. The frequency characteristics were also investigated and a bandwidth of 5% is predicted over which the cross-polarization remains below -30 dB, the input VSWR is below 1.15, and the phase error is less than 10 deg. Theoretical radiation patterns and efficiency curves for a paraboloidal reflector illuminated by this feed were computed. The predicted sidelobe level is below -30 dB and aperture efficiencies greater than 70% are possible. Experimental results are also presented that substantiates the theoretical results. In addition, experimental results for a 'short-cup' coaxial feed are given. The report includes extensive design data for the dual-mode feed along with performance curves showing cross-polarization as a function of feed parameters. The feed is useful for low-cost ground based receiving antennas for use in direct television satellite broadcasting service

Nanowire metamaterials with extreme optical anisotropy

We study perspectives of nanowire metamaterials for negative-refraction waveguides, high-performance polarizers, and polarization-sensitive biosensors. We demonstrate that the behavior of these composites is strongly influenced by the concentration, distribution, and geometry of the nanowires, derive an analytical description of electromagnetism in anisotropic nanowire-based metamaterials, and explore the limitations of our approach via three-dimensional numerical simulations. Finally, we illustrate the developed approach on the examples of nanowire-based high energy-density waveguides and non-magnetic negative index imaging systems with far-field resolution of one-sixth of vacuum wavelength.Comment: Updated version; accepted to Appl.Phys.Let

Center of mass rotation and vortices in an attractive Bose gas

The rotational properties of an attractively interacting Bose gas are studied using analytical and numerical methods. We study perturbatively the ground state phase space for weak interactions, and find that in an anharmonic trap the rotational ground states are vortex or center of mass rotational states; the crossover line separating these two phases is calculated. We further show that the Gross-Pitaevskii equation is a valid description of such a gas in the rotating frame and calculate numerically the phase space structure using this equation. It is found that the transition between vortex and center of mass rotation is gradual; furthermore the perturbative approach is valid only in an exceedingly small portion of phase space. We also present an intuitive picture of the physics involved in terms of correlated successive measurements for the center of mass state.Comment: version2, 17 pages, 5 figures (3 eps and 2 jpg

Landau-Zener-St\"uckelberg Spectroscopy of a Superconducting Flux Qubit

We proposed a new method to measure the energy spectrum of a superconducting flux qubit. Different from the conventional frequency spectroscopy, a short triangle pulse is used to drive the qubit through the anticrossing and generates Landau-Zener-St\"uckelberg interference patterns, from which the information of the energy spectrum can be extracted. Without installing microwave lines one can simplify the experimental setup and reduce the unwanted effects of noise. Moreover, the method can be applied to other quantum systems, opening the possibility of calibrating and manipulating qubits with linear pulses.Comment: 7 pages, 5 figure