39,547 research outputs found
The study of microstrip antenna arrays and related problems
The physical layout of the array elements and the proximity of the microstrip feed network makes the input impedance and radiation pattern values dependent upon the effects of mutual coupling, feedline discontinuities and feed point location. The extent of these dependences was assessed and a number of single patch and module structures were constructed and measured at an operating frequency of approximately 4.0 GHz. The empirical results were compared with the ones which were theoretically predicted by the cavity model of thin microstrip antennas. Each element was modelled as an independent radiating patch and each microstrip feedline as an independent, quasi-TEM transmission line. The effects of the feedline discontinuities are approximated by lumped L-C circuit models
Theory of the Three-Group Evolutionary Minority Game
Based on the adiabatic theory for the evolutionary minority game (EMG) that
we proposed earlier[1], we perform a detail analysis of the EMG limited to
three groups of agents. We derive a formula for the critical point of the
transition from segregation (into opposing groups) to clustering (towards
cautious behaviors). Particular to the three-group EMG, the strategy switching
in the "extreme" group does not occur at every losing step and is strongly
intermittent. This leads to an correction to the critical value of the number
of agents at the transition, . Our expression for is in agreement
with the results obtained from our numerical simulations.Comment: 4 pages and 2 figure
Random bipartite entanglement from W and W-like states
We describe a protocol for distilling maximally entangled bipartite states
between random pairs of parties from those sharing a tripartite W state, and
show that, rather surprisingly, the total distillation rate (the total number
of EPR pairs distilled per W, irrespective of who shares them) may be done at a
higher rate than distillation of bipartite entanglement between specified pairs
of parties. Specifically, the optimal distillation rate for specified
entanglement for the W has been previously shown to be the asymptotic
entanglement of assistance of 0.92 EPR pairs per W, while our protocol can
asymptotically distill 1 EPR pair per W between random pairs of parties, which
we conjecture to be optimal. We thus demonstrate a tradeoff between the overall
asymptotic rate of EPR distillation and the distribution of final EPR pairs
between parties. We further show that by increasing the number of parties in
the protocol that there exist states with fixed lower-bounded distillable
entanglement for random parties but arbitrarily small distillable entanglement
for specified parties.Comment: 5 pages, 1 figure, RevTeX. v2 - upper bound on random distillation is
expressed more generally and corollaries to the bound added. Minor notation
changes. v3 - further notation changes (Ernd now designated Et), discussion
of finite distillation rounds and single-copy bound on Et added. Theorem
added - relative entropy is shown to be an upper bound to Et for all pure
states. Discussion of W formation from EPRs (previously shown in others'
work) removed. Some addition, removal and reordering of reference
Numerical methods for analyzing electromagnetic scattering
The wave propagation inside a cylindrical waveguide, coated with lossy dielectric material due to the incidence of a plane wave at the open end of the guide, was studied. The general properties of the normal mode propagation were investigated
Theory of the evolutionary minority game
We present a theory which describes a recently introduced model of an
evolving, adaptive system in which agents compete to be in the minority. The
agents themselves are able to evolve their strategies over time in an attempt
to improve their performance. The present theory explicitly demonstrates the
self-interaction, or so-called market impact, that agents in such systems
experience
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Ontogenetic shifts in perceptions of safety along structural complexity gradients in a territorial damselfish.
Age and body size can influence predation risk and hence habitat use. Many species undergo ontogenetic shifts in habitat use as individuals grow larger and have different age-specific predation pressures. On coral reefs, a number of fish species are more tolerant of threats in structurally complex habitats that contain more refuges than in less structurally complex habitats. However, we do not know how risk perception varies with age, and whether age interacts with habitat complexity. Adults and juveniles, because of their size, may face different risks in structurally simple versus complex habitats. We used flight initiation distance as a metric to analyze perceptions of risk in a species of damselfish Stegastes nigricans. All else being equal, fish fleeing at greater distances are inferred to perceive higher risk. We targeted juvenile and adult damselfish to assess whether there are ontogenetic shifts in perceptions of safety in relation to structural complexity, inferred based on percent coral cover and rugosity. We found that adult damselfish tolerated closer approach in more complex habitats as measured by percent coral cover, but not rugosity, whereas juvenile fish always allowed closer approach than adult fish regardless of complexity. This ontogenetic shift in habitat use may result from juvenile fish taking bigger risks to maximize growth, whereas older animals, who are closer to their maximum body size, can afford to take fewer risks and protect their assets
The Health Care Safety Net and Crowd-Out of Private Health Insurance
There is an extensive literature on the extent to which public health insurance coverage through Medicaid induces less private health insurance coverage. However, little is known about the effect of other components of the health care safety net in crowding out private coverage. We examine the effect of Medicaid and uncompensated care provided by clinics and hospitals on insurance coverage. We construct a long panel of metropolitan area and state-level data on hospital uncompensated care and free and reduced price care offered by Federally Qualified Health Centers. We match this information to individual level data on coverage from the Current Population Survey for two distinct groups: children aged 14 and under and single, childless adults aged 18 to 64. Our results provide mixed evidence on the extent of crowd-out. Hospital uncompensated care does not appear to crowd-out health insurance coverage and health center uncompensated care appears to crowd-out private coverage for adults and, in some specifications, children.
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