81 research outputs found
Characteristic modes â progress, overview, and emerging topics
Over the past decade, characteristic mode analysis (CMA) research has grown from a niche topic to a mainstream topic, warranting a tutorial-style special issue to survey the signiïŹcant progress that has been made in this ïŹeld. In thisintroductory article (PAPER 1), the focus is on providing the big picture. We start with a simple description of characteristic modes. Next, we examine the trends in this ïŹeld, followed by providing further insights into CMAâs historical development. We will also address common myths surrounding the subject. Then, leaving the detailed coverage of major topics to the following papers, we summarize recent applications of CMA in scattering and other emerging topics. Finally, we conclude with some future perspectives on this ïŹeld
Capacity analysis for compact MIMO systems
We analyze the impact of mutual coupling on the capacity of MEMO systems with compact antenna arrays. Existing studies present conflicting views on the effect of mutual coupling. This is, in part, due to their different scopes and underlying assumptions of the system setups. In this paper, we aim to give a comprehensive picture by first examining the impact of mutual coupling on three capacity-related performance measures: antenna correlation, efficiency and bandwidth. While the first two aspects have received significant attention, antenna bandwidth with mutual coupling is a relatively uncharted territory. We show that while implementing a good matching network can drastically improve the system capacity for narrowband systems in the presence of strong mutual coupling, the same conclusions may not necessarily apply to wideband cases. To exemplify this, we carry out capacity simulations for an end-to-end MIMO system, where a recently proposed S-parameter approach is used in conjunction with the 3GPP-3GPP2 channel model to model realistic wideband channel and antenna effects at both transmit and receive ends
The Longitudinal Polarimeter at HERA
The design, construction and operation of a Compton back-scattering laser
polarimeter at the HERA storage ring at DESY are described. The device measures
the longitudinal polarization of the electron beam between the spin rotators at
the HERMES experiment with a fractional systematic uncertainty of 1.6%. A
measurement of the beam polarization to an absolute statistical precision of
0.01 requires typically one minute when the device is operated in the
multi-photon mode. The polarimeter also measures the polarization of each
individual electron bunch to an absolute statistical precision of 0.06 in
approximately five minutes. It was found that colliding and non-colliding
bunches can have substantially different polarizations. This information is
important to the collider experiments H1 and ZEUS for their future
longitudinally polarized electron program because those experiments use the
colliding bunches only.Comment: 21 pages (Latex), 14 figures (EPS
Benchmark problem definition and cross-validation for characteristic mode solvers
In October 2016, the Special Interest Group on Theory of Characteristic Modes (TCM) initiated a coordinated effort to perform benchmarking work for characteristic mode (CM) analysis. The primary purpose is to help improve the reliability and capability of existing CM solvers and to provide the means for validating future tools. Significant progress has already been made in this joint activity. In particular, this paper describes several benchmark problems that were defined and analyzes some results from the cross-validations of different CM solvers using these problems. The results show that despite differences in the implementation details, good agreement is observed in the calculated eigenvalues and eigencurrents across the solvers. Finally, it is concluded that future work should focus on understanding the impact of common parameters and output settings to further reduce variability in the results
Strong Decays of Strange Quarkonia
In this paper we evaluate strong decay amplitudes and partial widths of
strange mesons (strangeonia and kaonia) in the 3P0 decay model. We give
numerical results for all energetically allowed open-flavor two-body decay
modes of all nsbar and ssbar strange mesons in the 1S, 2S, 3S, 1P, 2P, 1D and
1F multiplets, comprising strong decays of a total of 43 resonances into 525
two-body modes, with 891 numerically evaluated amplitudes. This set of
resonances includes all strange qqbar states with allowed strong decays
expected in the quark model up to ca. 2.2 GeV. We use standard nonrelativistic
quark model SHO wavefunctions to evaluate these amplitudes, and quote numerical
results for all amplitudes present in each decay mode. We also discuss the
status of the associated experimental candidates, and note which states and
decay modes would be especially interesting for future experimental study at
hadronic, e+e- and photoproduction facilities. These results should also be
useful in distinguishing conventional quark model mesons from exotica such as
glueballs and hybrids through their strong decays.Comment: 69 pages, 5 figures, 39 table
Observation of a 1750 MeV/c^2 Enhancement in the Diffractive Photoproduction of K^+K^-
Using the FOCUS spectrometer with photon beam energies between 20 and 160
\gev, we confirm the existence of a diffractively photoproduced enhancement in
at 1750 \mevcc with nearly 100 times the statistics of previous
experiments. Assuming this enhancement to be a single resonance with a
Breit-Wigner mass shape, we determine its mass to be
\mevcc and its width to be \mevcc. We find no
corresponding enhancement at 1750 \mevcc in , and again neglecting any
possible interference effects we place limits on the ratio . Our results are consistent with previous
photoproduction experiments, but, because of the much greater statistics,
challenge the common interpretation of this enhancement as the
seen in annihilation experiments.Comment: 10 pages, 5 figure
Probing the strength of infants' preference for helpers over hinderers:Â two replication attempts of Hamlin and Wynn (2011)
Several studies indicate that infants prefer individuals who act prosocially over those
who act antisocially toward unrelated third parties. In the present study, we focused on a
paradigm published by Kiley Hamlin and Karen Wynn in 2011. In this study, infants were
habituated to a live puppet show in which a protagonist tried to open a box to retrieve a toy
placed inside. The protagonist was either helped by a second puppet (the âHelperâ), or hindered by a third puppet (the âHindererâ). At test, infants were presented with the Helper and the Hinderer, and encouraged to reach for one of them. In the original study, 75% of 9-month-olds selected the Helper, arguably demonstrating a preference for prosocial over antisocial individuals. We conducted two studies with the aim of replicating this result. Each
attempt was performed by a different group of experimenters. Study 1 followed the methods
of the published study as faithfully as possible. Study 2 introduced slight modifications to the
stimuli and the procedure following the guidelines generously provided by Kiley Hamlin and
her collaborators. Yet, in our replication attempts, 9-month-oldsâ preference for helpers over hinderers did not differ significantly from chance (62.5% and 50%, respectively, in Studies 1 and 2). Two types of factors could explain why our results differed from those of Hamlin and Wynn: minor methodological dissimilarities (in procedure, materials, or the population
tested), or the effect size being smaller than originally assumed. We conclude that fine
methodological details that are crucial to infantsâ
success in this task need to be identified to
ensure the replicability of the original result
K^* Mesons and Nucleon Strangeness
We study contributions to the nucleon strange quark vector current form
factors from intermediate states containing K^* mesons. We show how these
contributions may be comparable in magnitude to those made by K mesons, using
methods complementary to those employed in quark model studies. We also analyze
the degree of theoretical uncertainty associated with K^* contributions.Comment: 21 pages, RevTex, 2 PS figures included with epsf.st
Results of final focus test beam
International audienceThe beam experiments of Final Focus Test Beam (FFTB) started in September 1993 at SLAC, and have produced a 1.7 ÎŒmĂ75 nm spot of 46 GeV electron beam. A number of new techniques involving two nanometer spot-size monitors have been developed. Several beam diagnostic/tuning schemes are applied to achieve and maintain the small spot. This experiment opens the way toward the nanometer world for future linear collider
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