3,645 research outputs found
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 MnVO 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
19 K and 11.8 K indicating two distinct magnetically
ordered phases. The single crystal neutron diffraction study shows that in the
temperature () range 11.8 K 19 K the magnetic structure is
commensurate with propagation vector , while upon lowering
temperature below 11.8 K an incommensurate magnetic order emerges
with and the magnetic structure can be represented by
cycloidal modulation of the Mn spin in 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
The Implementation of the Global Minimum Tax (GloBE): The Need for an Effective Dispute Prevention and Resolution Mechanism
The successful implementation of the Global Anti-Base Erosion (GloBE) rules on aglobal scale cannot be achieved without an international effective dispute prevention and reso-lution mechanism. However, the development of a dispute prevention and resolution frameworkfor the GloBE rules faces significant challenges. This article offers two possible options for aneffective dispute prevention and resolution mechanism: a model based on reciprocal domesticlegislations and the multilateral convention model
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, NdZrO. Powder x-ray
diffraction analysis confirms that NdZrO 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 ions in the ground state. Specific heat versus temperature
measurements in zero applied magnetic field indicate the presence of a thermal
anomaly below 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
Cerebellar volume is linked to cognitive function in temporal lobe epilepsy: A quantitative MRI study
AbstractIntroductionChronic intractable temporal lobe epilepsy (TLE) is associated with certain comorbidities including cognitive impairment. A less common condition among patients with TLE is intermittent explosive disorder (IED), a specific form of aggressive behavior that has been linked to low intelligence and structural pathology in the amygdala. We aimed to identify other neuroanatomical substrates of both cognitive dysfunction and IED in patients with TLE, with special focus on the cerebellum, a brain region known to participate in functional networks involved in neuropsychological and affective processes.MethodsMagnetic resonance imaging-based volumetric data from 60 patients with temporal lobe epilepsy (36 with and 24 without IED) were evaluated. Cerebellar, hippocampal, and total brain volumes were processed separately. In a total of 50 patients, the relationship between volumetric measurements and clinical and neuropsychological data (full-scale, verbal, and performance intelligence quotients) was analyzed.ResultsIntermittent explosive disorder in patients with TLE was not significantly linked to any of the regional volumes analyzed. However, cognitive performance showed a significant association both with total brain volume and cerebellar volume measurements, whereby the left cerebellar volume showed the strongest association. A deviation from normal cerebellar volumes was related to lower intelligence. Of note, left cerebellar volume was influenced by age and duration of epilepsy. Hippocampal volumes had a minor influence on cognitive parameters.ConclusionOur findings suggest that cerebellar volume is not linked to IED in patients with TLE but is significantly associated with cognitive dysfunction. Our findings support recent hypotheses proposing that the cerebellum has a relevant functional topography
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