Photorealistic ray tracing of free-space invisibility cloaks made of uniaxial dielectrics

The design rules of transformation optics generally lead to spatially inhomogeneous and anisotropic impedance-matched magneto-dielectric material distributions for, e.g., free-space invisibility cloaks. Recently, simplified anisotropic non-magnetic free-space cloaks made of a locally uniaxial dielectric material (calcite) have been realized experimentally. In a two-dimensional setting and for in-plane polarized light propagating in this plane, the cloaking performance can still be perfect for light rays. However, for general views in three dimensions, various imperfections are expected. In this paper, we study two different purely dielectric uniaxial cylindrical free-space cloaks. For one, the optic axis is along the radial direction, for the other one it is along the azimuthal direction. The azimuthal uniaxial cloak has not been suggested previously to the best of our knowledge. We visualize the cloaking performance of both by calculating photorealistic images rendered by ray tracing. Following and complementing our previous ray-tracing work, we use an equation of motion directly derived from Fermats principle. The rendered images generally exhibit significant imperfections. This includes the obvious fact that cloaking does not work at all for horizontal or for ordinary linear polarization of light. Moreover, more subtle effects occur such as viewing-angle-dependent aberrations. However, we still find amazingly good cloaking performance for the purely dielectric azimuthal uniaxial cloak.Comment: 12 pages, 3 figures, journal pape

Conformal carpet and grating cloaks

We introduce a class of conformal versions of the previously introduced quasi-conformal carpet cloak, and show how to construct such conformal cloaks for different cloak shapes. Our method provides exact refractive-index profiles in closed mathematical form for the usual carpet cloak as well as for other shapes. By analyzing their asymptotic behavior, we find that the performance of finite-size cloaks becomes much better for metal shapes with zero average value, e.g., for gratings.Comment: added Ref. 12; added 2 figures; reformatte

Reactivity and Characterization of Intermetallic Alloy Catalysts for Alkane Dehydrogenation

As the United States works towards energy independence shale gas has become an attractive domestic recourse for use as a feedstock to produce fuels. One potential approach to utilize shale gas is to first convert the C2 and C3 paraffinic components into olefins, valuable chemical building blocks, by catalytic dehydrogenation. The goal of this dissertation is to study how the geometric and electronic changes to a metal upon alloying influence its selectivity for light alkane dehydrogenation. In the first three projects bimetallic catalysts comprising of either Pd or Pt and a post-transition metal known to promote olefin selectivity were investigated. In all the systems studied the bimetallic catalysts were found to be more selective for ethane dehydrogenation than the monometallic analogue. In situ characterizations revealed the formation of intermetallic compounds (IMC) which contained either small ensembles of or completely isolated active atoms in the bimetallic catalysts. It is believed that these geometric changes to the active metal are the dominant factor leading to improved dehydrogenation selectivities. From a study performed on Pd-In catalysts it was proposed that IMC structures similar to the active metal are preferentially formed. In a separate study, two distinct IMC structures were formed in Pt-In catalysts with different In:Pt atomic ratios and the two phases were found to have different turnover rates (TOR) and apparent activation energies. These results showed that the catalytic properties of metals could be altered by forming different IMC structures. Lastly, a study on Pt-Zn catalysts revealed changes in energy of the 5d states of Pt upon IMC formation. The observed energy change is believed to be responsible for increases in dehydrogenation TOR. In the fourth project Pt-Fe bimetallic catalysts were investigated as an extrapolation of the findings of the first set of studies. Pt and Fe were found to form three IMC structures as the Fe:Pt atomic ratio was varied. All three structures contained Pt atoms with local geometries identical to the catalysts selective for ethane dehydrogenation. When tested for propane dehydrogenation the IMC catalysts were found to be highly selective for propylene. Although Pt and Fe are both catalytic, the much higher activity of the former results in the latter behaving as an inert diluent. This results in the small ensembles of and isolated Pt atoms in the IMC structures being highly selective for dehydrogenation. Electronic structure measurements and calculations showed small changes in the average energies of the 5d states of Pt as the Fe content of the IMC changed. Associated with the valance energy shifts were changes in metal-adsorbate bond strengths which were believed to be the cause of increased dehydrogenation TOR. These results demonstrated that it is possible to change the electronic structure of metals by forming IMCs with different promoters or stoichiometries. While electronic effects play a secondary role in alkane dehydrogenation, this insight could provide useful for other catalytic chemistries

Decision Support Systems in Australian Agriculture: State of the Art and Future Development

This paper reports and discusses the results of a survey conducted with experts working in the field of decision support systems (DSS) in Australian agriculture. It also reviews the literature on DSS in the light of these experts' responses. The findings from this survey have consolidated our understanding of the current state of DSS in Australian agriculture. The uptake of DSS by farmers has been slow and various issues said to be contributing to this include fear of using computers, time constraints, poor marketing, complexity, lack of local relevance, lack of end-user involvement, and mismatched objectives between developers and users. The future prospect for the development of DSS was generally regarded to be poor. Never-the-less, the authors believe that new DSS which embrace the suggested criteria could be widely accepted by farmers. These criteria mean that to be widely used by farmers, any successful DSS needs to address widespread problems: they need to be location specific, and gain strong support from initial users. They also need to be simple to use, relevant, effective, low cost, and user friendly and it is most likely that farmers would have been involved in their development. We believe that farmers' personalities, and their attitudes towards risk management and decision making, will influence the pattern of adoption of DSS in Australian agriculture while the intergenerational change that is occurring in the management of Australian farms is a positive factor that may encourage more widespread use of these tools.DSS, farmers' decision-making, expert opinion, management decisions, Farm Management, D7, D8, Q12, Q13, Q16,

Teaching Physics Using Virtual Reality

We present an investigation of game-like simulations for physics teaching. We report on the effectiveness of the interactive simulation "Real Time Relativity" for learning special relativity. We argue that the simulation not only enhances traditional learning, but also enables new types of learning that challenge the traditional curriculum. The lessons drawn from this work are being applied to the development of a simulation for enhancing the learning of quantum mechanics

Investigation of new concepts of adaptive devices Quarterly technical report, 15 Jun. - 14 Sep. 1967

Insulated gate field effect transistor with adaptive and memory characteristic

Twisted split-ring-resonator photonic metamaterial with huge optical activity

Coupled split-ring-resonator metamaterials have previously been shown to exhibit large coupling effects, which are a prerequisite for obtaining large effective optical activity. By a suitable lateral arrangement of these building blocks, we completely eliminate linear birefringence and obtain pure optical activity and connected circular optical dichroism. Experiments at around 100-THz frequency and corresponding modeling are in good agreement. Rotation angles of about 30 degrees for 205nm sample thickness are derived.Comment: 6 pages, 4 figure

Self-consistent calculation of metamaterials with gain

We present a computational scheme allowing for a self-consistent treatment of a dispersive metallic photonic metamaterial coupled to a gain material incorporated into the nanostructure. The gain is described by a generic four-level system. A critical pumping rate exists for compensating the loss of the metamaterial. Nonlinearities arise due to gain depletion beyond a certain critical strength of a test field. Transmission, reflection, and absorption data as well as the retrieved effective parameters are presented for a lattice of resonant square cylinders embedded in layers of gain material and split ring resonators with gain material embedded into the gaps.Comment: 5 pages, 6 figure

Time-of-flight imaging of invisibility cloaks

As invisibility cloaking has recently become experimental reality, it is interesting to explore ways to reveal remaining imperfections. In essence, the idea of most invisibility cloaks is to recover the optical path lengths without an object (to be made invisible) by a suitable arrangement around that object. Optical path length is proportional to the time of flight of a light ray or to the optical phase accumulated by a light wave. Thus, time-of-flight images provide a direct and intuitive tool for probing imperfections. Indeed, recent phase-sensitive experiments on the carpet cloak have already made early steps in this direction. In the macroscopic world, time-of-flight images could be measured directly by light detection and ranging (LIDAR). Here, we show calculated time-of-flight images of the conformal Gaussian carpet cloak, the conformal grating cloak, the cylindrical free-space cloak, and of the invisible sphere. All results are obtained by using a ray-velocity equation of motion derived from Fermat’s principle