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Metamaterials are subwavelength man-made plasmonic or dielectric structures designed to realize specific effects on the electromagnetic radiation interacting with the material. Here we aim to rotate the polarization of an incident terahertz beam using chiral metamaterials, while suppressing the circular dichroism which induces ellipticity of the output beam. An incident linearly polarized wave can be decomposed into left-circularly and right-circularly polarized waves, and the difference in propagation phase will result in rotation of the plane of polarization. Since chiral structures couple electric and magnetic fields, they are often implemented in complex geometries such as spirals or bi-layered plasmonic structures, which can achieve carefully balanced responses to the two fields. The important feature of the bi-layered plasmonic structure is the cross-coupling between the resonances of the two layers. It is precisely this coupling between the layers that induces currents in the structures that are mutually dependent producing chirality within the structure. By coupling a metallic structure to its complement, we are able to achieve strong transmission in the region of maximum polarization rotation, and relatively low ellipticity of the output state. Three different structures were fabricated for this work that will be referred to as: the plain crosses, crossed arrowheads, and crossed arcs, pictured in the figure below. The terahertz responses of the structures were compared using terahertz time-domain spectroscopy and numerical simulations using CST Microwave Studio software.

The interplay between interlayer coupling and exchange bias coupling in [NiFe/Mn] multilayerbased thin films was investigated by using ion-beam bombardment during deposition to control the configurations from superlattice to nanocomposite or hybrid-structured thin films. Results showed that well-defined interfaces in the superlattice [NiFe/Mn] thin film exhibited an interlayer coupling behavior. In contrast, an enhanced coercivity was observed in the nanocomposite [NiFe-Mn] thin film. However, the hybrid [NiFe-Mn]/[NiFe/Mn] thin film with an intermixed NiFeMn alloyed film component gave rise to unusual positive exchange bias coupling.

W.-C. Chen , N. I. Landy , K. Kempa , and W. J. Padilla * IO N The study of light coupling to small apertures in metallic fi lms has a long and illustrious history. In 1897 Lord Rayleigh treated the problem by using the concept of effective dipoles. Most recently, researchers have made these apertures periodic, where they exhibited so-called extraordinary optical transmission (EOT) – transmission effi ciencies far in excess of unity at wavelengths greater than the lattice parameter of the surface. This behavior is not predicted by standard aperture theory as developed by Bethe in 1944, [ 1 ] nor was it noticed before fabricational and measurement techniques had advanced to the point that EOT could be observed at optical wavelengths. However, in 1998 Ebbesen et al. [ 2 ] showed EOT in the near-infrared and posited that this stemmed from plasmon coupling between surfaces. Since then, EOT [ 2–5 ] has been studied with increasing detail in both theoretical and experimental capacities. This result led to a fl urry of intense theoretical and experimental research to probe the nature of this extraordinary optical transmission. Babinet metamaterials [ 6–8 ] may also be described as periodic apertures in metal fi lms. Metamaterials are structured periodic metallic patterns which enable the construction of materials with specifi ed electromagnetic properties, some of which cannot be obtained via naturally occurring materials. [ 9,10 ] Metamaterials exhibit electromagnetic resonances where the resonant wavelength is signifi cantly larger than the physical dimensions of the individual elements. Thus metamaterials are subwavelength media and well described by the optical constants e and μ . [ 11 ] In transmission metamaterials (scatterers) yield an absorptive like minimum feature at resonance, but are otherwise highly transmissive outside of this band. In contrast Babinet metamaterials (apertures)—made by taking the ‘inverse’ metamaterial structure—yield opposite behavior and exhibit a transmission maxima near resonance. [ 12,13 ]

Thermal evolution of Co islands on Ag/Ge(111)-√3 × √3 and Ag/Si(111)-√3 × √3 surfaces was studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). Ag-√3 × √3 buffer layer can avoid alloy formation of Co and Si or Ge below the annealing temperature 500 °C. The growth behavior of Co on Ag/Si(111)-√3 × √3 surfaces is very different from that on Ag/Ge(111)-√3 × √3 surfaces, although both the √3 structures can be classified as honeycomb chain trimer (HCT) model. Submonolayer Co on Ag/Si(111)-√3 × √3 surfaces prefer to form clusters below 500 °C. However, Co clusters nucleate and construct two-dimensional islands (2D islands) on Ag/Ge(111)-√3 × √3 surfaces after annealing to 300 °C. The result of different growth behavior comes from two major factors. One is antiphase boundaries (APBs) with extra electron states, which trap Co clusters on Ag/Si(111)-√3 × √3 surfaces. The other is the strong binding force that exists between Ge and Co atoms to cause the formation of Co period islands on Ag/Ge(111)-√3 × √3 surfaces. Copyright © 2008 John Wiley & Sons, Ltd.

We propose a post-processing approach for tuning terahertz metamaterials by modifying the coupling between two metamaterial layers. We demonstrate that this method allows the metamaterial resonance to be shifted by 31% of the central frequency.

Chemical investigation of the organic extract of a soft coral belonging to the genus Alcyonium furnished a steroid, 3α,7α,12α-triacetoxy-5β-cholanic acid (1). The structure of steroid 1 was assigned on the basis of spectroscopic evidence, particularly in 1D and 2D NMR experiments. The configuration of steroid 1 was further supported by molecular mechanics calculations.

We present an experimental demonstration of electronically tunable metamaterial absorbers in the terahertz regime. By incorporation of active liquid crystal into strategic locations within the metamaterial unit cell, we are able to modify the absorption by 30% at 2.62 THz, as well as tune the resonant absorption over 4% in bandwidth. Numerical full-wave simulations match well to experiments and clarify the underlying mechanism, i.e., a simultaneous tuning of both the electric and magnetic response that allows for the preservation of the resonant absorption. These results show that fundamental light interactions of surfaces can be dynamically controlled by all-electronic means and provide a path forward for realization of novel applications.

Metamaterial absorbers have been demonstrated across much of the electromagnetic spectrum and exhibit both broad and narrow-band absorption for normally incident radiation. Absorption diminishes for increasing angles of incidence and transverse electric polarization falls off much more rapidly than transverse magnetic. We unambiguously demonstrate that broad-angle TM behavior cannot be associated with periodicity, but rather is due to coupling with a surface electromagnetic mode that is both supported by, and well described via the effective optical constants of the metamaterial where we achieve a resonant wavelength that is 19.1 times larger than the unit cell. Experimental results are supported by simulations and we highlight the potential to modify the angular response of absorbers by tailoring the surface wave.

We propose that macroscopic objects built from negative-permeability metamaterials may experience resonantly enhanced magnetic force in low-frequency magnetic fields. Resonant enhancement of the time-averaged force originates from magnetostatic surface resonances (MSR) which are analogous to the electrostatic resonances of negative-permittivity particles, well known as surface plasmon resonances in optics. We generalize the classical problem of MSR of a homogeneous object to include anisotropic metamaterials, and consider the most extreme case of anisotropy where the permeability is negative in one direction but positive in the others. It is shown that deeply subwavelength objects made of such indefinite (hyperbolic) media exhibit a pronounced magnetic dipole resonance that couples strongly to uniform or weakly inhomogeneous magnetic field and provides strong enhancement of the magnetic force, enabling applications such as enhanced magnetic levitation., 19 pages, 5 figures

We investigate the conditions under which single layer metamaterials may be described by bulk optical constants. Terahertz time domain spectroscopy is utilized to investigate two types of geometries, both with two different sizes of embedding dielectric---cubic and tetragonal unit cells. The tetragonal metamaterials are shown to yield layer dependent optical constants, whereas the cubic metamaterials yielded layer independent optical constants. We establish guidelines for when $\ensuremath{\epsilon}$ and $\ensuremath{\mu}$ can be used as material parameters for single layer metamaterials. Experimental results at terahertz frequencies are presented and supported by full wave three-dimensional electromagnetic simulations.

We present highly sub-wavelength magnetic metamaterials designed for operation at radio frequencies (RFs). A dual layer design consisting of independent planar spiral elements enables experimental demonstration of a unit cell size (a) that is ~ 700 times smaller than the resonant wavelength ({\lambda}0). Simulations indicate that utilization of a conductive via to connect spiral layers permits further optimization and we achieve a unit cell that is {\lambda}0/a ~ 2000. Magnetic metamaterials are characterized by a novel time domain method which permits determination of the complex magnetic response. Numerical simulations are performed to support experimental data and we find excellent agreement. These new designs make metamaterial low frequency experimental investigations practical and suggest their use for study of magneto-inductive waves, levitation, and further enable potential RF applications., Comment: 5 pages, 4 figures

International audience; We computationally and experimentally investigate the use of metamaterial resonators as bandpass filters and other components that enable control of guided surface electromagnetic waves. The guided surface electromagnetic wave propagates on a planar Goubau line, launched via a coplanar waveguide coupler with 50Ω impedance. Experimental samples targeted for either microwave or terahertz frequencies are measured and shown to be in excellent agreement with simulations. Metamaterial elements are designed to absorb energy only of the planar Goubau line and yield narrow-band resonances with relatively high quality factors. Two independent configurations of coupled metamaterial elements are demonstrated that modify the otherwise flat transmission spectrum of the planar Goubau line. By physically shunting the capacitive gaps of the coupled metamaterial elements, we demonstrate the potential for a large dynamic range in transmissivity, suggesting the use of this configuration for high-bandwidth terahertz communications.

To improve competitive advantage and operational performances of supply chains, we implement multi-agent supply chain modeling with learning capability to predict order arrival times that manufacturers can pre-produce to shorten order lead time for downstream customer orders. As order lead time is reduced, bullwhip effect of supply chains would also be minimized. Two kinds of learning agents are embedded in traditional supply chains to learn from past experiences to predict next order arrival time. We use back propagation neural networks and an order arrival pattern matching (OAPM) algorithm with belief set models for the prediction. The performances are compared with the traditional supply chain and the VMI-based supply chain. Results show that even with tailored learning intelligence, the VMI-based supply chain still performs better than the others. However, the two supply chains with learning agents outperform the traditional supply chain. This implies that learning intelligence can assist in predicting order arrival times, but information sharing seems to do it even better.

Chemical investigation of the organic extract of a soft coral belonging to the genus Alcyonium furnished a steroid, 3alpha,7alpha,12alpha-triacetoxy-5beta-cholanic acid (1). The structure of steroid 1 was assigned on the basis of spectroscopic evidence, particularly in 1D and 2D NMR experiments. The configuration of steroid 1 was further supported by molecular mechanics calculations.

We propose a post-processing approach to efficiently tune the resonance frequency in doublelayered terahertz metamaterials separated by a bonding agent. By heating the bonding agent, it is possible to move one metamaterial layer laterally with respect to the other. This changes the coupling between adjacent layers, thereby shifting the resonance frequency. The resonance frequency of the stacked layers continuously shifts as a function of the lateral displacement, reaching a maximum shift of 92GHz (31% of the center frequency). We discuss the effects of vertical separation on the tunability of the two-layered structure. The post-processing approach is rather general and can be applied to different paired metamaterials in various wavelength ranges, paving the way to efficiently assemble and fine tune metamaterial sensors and filters. V C 2014 AIP Publishing LLC.

We study interaction of the electromagnetic radiation with a series of thin film periodic nanostructures evolving from holes to islands. We show, through model calculations, simulations, and experiments, that the responses of these structures evolve accordingly, with two topologically distinct spectral types for holes and islands. We find also, that the response at the transitional pattern is singular. We show that the corresponding effective dielectric function follows the critical behavior predicted by the percolation theory and thus the hole-to-island structural evolution in this series is a topological analog of the percolation problem, with the percolation threshold at the transitional pattern.

The asymptotic distributions of the size distributions of the symmetric Dirichlet-Multinomial urn model are investigated. By allowing the number of ballsn and number of urnsm to go to infinity at different rates we can get both Poisson limit distributions and normal limit distributions. In either case some local limit theorems are obtained. We also consider a more general urn scheme where the number of balls is considered as a random variable depending on the number of urns; some interesting limit theorems are also obtained in this context.

Zipf's laws are probability distributions on the positive integers which decay algebraically. Such laws have been shown empirically to describe a large class of phenomena, including frequency of words usage, populations of cities, distributions of personal incomes, and distributions of biological genera and species, to mention only a few. In this paper we present a Dirichlet–multinomial urn model for describing the above phenomena from a stochastic point of view. We derive the Zipf's law under certain regularity conditions; some limit theorems are also obtained for the urn model under consideration.

Let X 1, X 2, · ··, Xn , · ·· be independent and identically distributed non-negative integer-valued random variables with finite mean and variance. For any positive integer n and m we consider the random vector i.e., L has the same distribution as the conditional distribution of (X 1, · ··, Xm ) given the condition It is easy to see that our model includes the classical urn model, the Bose–Einstein urn model and the Pólya urn model as special cases. For any non-negative integer s define G(s) = the number of Li′s such that Li = s, and U = the number of Li′s such that Li is an even number; in this paper we study the asymptotic behaviour of the random variables considered above. Some central limit theorems and a multinormal local limit theorem are proved.

Stationary processes whose restrictions are totally bounded in variation distance are shown to be equivalent to the class of tight measures when the alphabet is countable. For uncountable alphabets, total boundedness implies tightness, but the reverse implication need not hold, as shown by example. Necessary and sufficient conditions for the class of Gaussian processes to be bounded totally are presented. An application of these results to universal coding for composite sources is considered.

Twenty-seven patients with mediastinal Hodgkin disease were treated either by radiation therapy or chemotherapy. The rates of tumor regression were measured and were fitted into a three-parameter Gompertzian model. Tumor regression was more pronounced and prompt in patients treated with radiotherapy. The Gompertzian model matched the radiation therapy data closely in the first 90 days after initiation of therapy in cases of approximately equal tumor size.