Rectenna session: Micro aspects

Two micro aspects of the rectenna design are addressed: evaluation of the degradation in net rectenna RF to DC conversion efficiency due to power density variations across the rectenna (power combining analysis) and design of Yagi-Uda receiving elements to reduce rectenna cost by decreasing the number of conversion circuits (directional receiving elements). The first of these micro aspects involves resolving a fundamental question of efficiency potential with a rectenna, while the second involves a design modification with a large potential cost saving

Solar power satellite rectenna design study: Directional receiving elements and parallel-series combining analysis

Rectenna conversion efficiencies (RF to dc) approximating 85 percent were demonstrated on a small scale, clearly indicating the feasibility and potential of efficiency of microwave power to dc. The overall cost estimates of the solar power satellite indicate that the baseline rectenna subsystem will be between 25 to 40 percent of the system cost. The directional receiving elements and element extensions were studied, along with power combining evaluation and evaluation extensions

Commensurate to incommensurate magnetic phase transition in Honeycomb-lattice pyrovanadate Mn2V2O7

We have synthesized single crystalline sample of Mn$_2$V$_2$O$_7$ using floating zone technique and investigated the ground state using magnetic susceptibility, heat capacity and neutron diffraction. Our magnetic susceptibility and heat capacity reveal two successive magnetic transitions at $T_{N1} =$ 19 K and $T_{N2} =$ 11.8 K indicating two distinct magnetically ordered phases. The single crystal neutron diffraction study shows that in the temperature ($T$) range 11.8 K $\le T \le$ 19 K the magnetic structure is commensurate with propagation vector $k_1 = (0, 0.5, 0)$, while upon lowering temperature below $T_{N2} =$ 11.8 K an incommensurate magnetic order emerges with $k_2 = (0.38, 0.48, 0.5)$ and the magnetic structure can be represented by cycloidal modulation of the Mn spin in $ac-$plane. We are reporting this commensurate to incommensurate transition for the first time. We discuss the role of the magnetic exchange interactions and spin-orbital coupling on the stability of the observed magnetic phase transitions.Comment: 8 pages, 7 figure

Predicting the contributions of novel marine prey resources from angling and anadromy to the diet of a freshwater apex predator

1. Anadromous fishes can be important prey resources for piscivorous fauna in lowland rivers. Freshwater anglers exploiting large-bodied cypriniform fishes use high quantities of pelletized marine fishmeal baits that can contribute substantially to fish diets. This marine-derived energy pathway also potentially provides a marine prey resource for freshwater piscivores. However, large-bodied cypriniform fishes are often in a size refuge against predation due to their large sizes. 2. Stable isotope (δ15N and δ13C) analysis assessed how novel marine prey resources influenced the diet of a freshwater apex predator, Northern pike Esox lucius, in an impounded river basin (lower River Severn, Western England). Up to three groups of prey resources were present: anadromous European shad (Alosa spp.), cypriniform fishes with dietary specialisms based on marine fishmeal baits, and freshwater prey. The availability of these prey resources to E. lucius varied according to river connectivity and levels of angling exploitation in different river reaches. 3. Where the three prey groups were present, E. lucius were more enriched in δ13C values (range: -24.74 to -16.34 ‰) compared to river reaches where aspects of the marine prey groups were absent. (range: -28.30 to -21.47) In all reaches, δ13C increased as E. lucius length increased. In the reach where all prey groups were present, the isotopic niches of three E. lucius size classes were strongly partitioned; this was not apparent in reaches where the marine pathways were unavailable. 4. Stable isotope mixing models suggested that freshwater prey were the most important prey item, contributing between 42 and 96 % to the diet of individual E. lucius. However, where present, anadromous fishes and cypriniform fishes specialising on marine fishmeal baits were also important prey items, contributing substantially to the diet of larger E. lucius (length > 650 mm). The total dietary contributions of the marine resources varied considerably among the individual larger fish (22 to 58 % of total diet). 5. The presence of two marine resource pathways in a lowland river thus strongly influenced the diet of an apex predator, but with contributions being a function of their spatial availability, E. lucius body size and individual trophic specialisations. These results emphasise how the anthropogenic activities of river engineering and human subsidies can affect the trophic dynamics of apex predators

Structural and Magnetic Investigations of Single-Crystals of the Neodymium Zirconate Pyrochlore, Nd2Zr2O7

We report structural and magnetic properties studies of large high quality single-crystals of the frustrated magnet, Nd$_2$Zr$_2$O$_7$. Powder x-ray diffraction analysis confirms that Nd$_2$Zr$_2$O$_7$ adopts the pyrochlore structure. Room-temperature x-ray diffraction and time-of-flight neutron scattering experiments show that the crystals are stoichiometric in composition with no measurable site disorder. The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 0.5 K. Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments. Magnetization versus field measurements show a local Ising anisotropy along the axes of the Nd$^{3+}$ ions in the ground state. Specific heat versus temperature measurements in zero applied magnetic field indicate the presence of a thermal anomaly below $T\sim7$ K, but no evidence of magnetic ordering is observed down to 0.5 K. The experimental temperature dependence of the single-crystal bulk dc susceptibility and isothermal magnetization are analyzed using crystal field theory and the crystal field parameters and exchange coupling constants determined.Comment: 10 pages, 6 figures, 4 tables. Accepted for publication in Physical Review

Grover's algorithm on a Feynman computer

We present an implementation of Grover's algorithm in the framework of Feynman's cursor model of a quantum computer. The cursor degrees of freedom act as a quantum clocking mechanism, and allow Grover's algorithm to be performed using a single, time-independent Hamiltonian. We examine issues of locality and resource usage in implementing such a Hamiltonian. In the familiar language of Heisenberg spin-spin coupling, the clocking mechanism appears as an excitation of a basically linear chain of spins, with occasional controlled jumps that allow for motion on a planar graph: in this sense our model implements the idea of "timing" a quantum algorithm using a continuous-time random walk. In this context we examine some consequences of the entanglement between the states of the input/output register and the states of the quantum clock

Via-First Inter-Wafer Vertical Interconnects utilizing Wafer-Bonding of Damascene-Patterned Metal/Adhesive Redistribution Layers

ABSTRACT Three-dimensional (3D) integration with through-die vias offer improved electrical performance compared to edgeconnected wire bonds in stacked-die assemblies. Monolithic wafer-level 3D integration offers the potential for a high density of micron-sized through-die vias necessary for highest performance of integrated systems. In addition, such wafer-level technologies offer the potential of lowest cost in large manufacturing volume of any heterogeneous integration platform, incorporating the inherent low cost of monolithic IC interconnectivity. After a brief summary of current 3D integration technologies, a recently introduced platform that offers the process integration advantage of copper-to-copper (Cu-to-Cu) bonding with the increased adhesion strength and robustness of dielectric adhesive bonding using benzocyclobutene (BCB) is discussed. Critical processing challenges of the new platform include BCB partial curing compatible with damascene patterning, post-damascene-patterning cleaning and surface activation, bonding process parameters, and wafer-level planarization requirements. The inherent incorporation of a redistribution layer into the bonding layer process further reduces the process flow and is compatible with waferlevel packaging (WLP) technologies. 3D IC TECHNOLOGIES Three major 3D IC approaches being pursued are: 1) die-to-die, 2) hybrid die-to-wafer, and 3) monolithic wafer-towafer 3D integrations, as shown in Both die-to-wafer and wafer-to-wafer approaches are expected to yield better performance than conventional chipto-chip or multi-chip packaging integration due to lower parasitics (both RC delay and inductance), because of shorter inter-chip connections. Both approaches also allow the integration of sub-blocks within circuits for added design flexibility and optimization capability due to denser inter-chip interconnectivity, while maintaining the separation of incompatible processes on different wafers. However, there are significant differences between these two approaches. The die-to-wafer approach offers the use of known-good-die (KGD

RF/Microwave Non-Destructive Measurements of Electrical Properties of Semiconductor Wafers for Thermophotovoltaic Applications

A radio-frequency/microwave measurement system has been designed for non-contacting determination of sheet resistance and excess carrier lifetime of low-bandgap materials and junctions, specifically GaSb-based alloys for thermophotovoltaic (TPV) applications. The design incorporates RF circuitry in the 100--500 MHz frequency range and utilizes a Q-switched YAG laser at 1.32 microns to photo-generate electron-hole pairs and conductivity modulate the material and/or junction under test. Supplementary measurements with a GaAs pulsed diode laser at 904 nm provides a faster transient response with near-surface photogeneration. Initial measurements on GaSb substrates, Zn-diffused materials and epitaxially grown layers are presented and discussed

Cooling atoms into entangled states

We discuss the possibility of preparing highly entangled states by simply cooling atoms into the ground state of an applied interaction Hamiltonian. As in laser sideband cooling, we take advantage of a relatively large detuning of the desired state, while all other qubit states experience resonant laser driving. Once spontaneous emission from excited atomic states prepares the system in its ground state, it remains there with a very high fidelity for a wide range of experimental parameters and all possible initial states. After presenting the general theory, we discuss concrete applications with one and two qubits.Comment: 16 pages, 6 figures, typos correcte