14,210 research outputs found
The influence of piezoceramic stack location on nonlinear behavior of langevin transducers
Power ultrasonic applications such as cutting, welding, and sonochemistry often use Langevin transducers to generate power ultrasound. Traditionally, it has been proposed that the piezoceramic stack of a Langevin transducer should be located in the nodal plane of the longitudinal mode of vibration, ensuring that the piezoceramic elements are positioned under a uniform stress during transducer operation, maximizing element efficiency and minimizing piezoceramic aging. However, this general design rule is often partially broken during the design phase if features such as a support flange or multiple piezoceramic stacks are incorporated into the transducer architecture. Meanwhile, it has also been well documented in the literature that power ultrasonic devices driven at high excitation levels exhibit nonlinear behaviors similar to those observed in Duffing-type systems, such as resonant frequency shifts, the jump phenomenon, and hysteretic regions. This study investigates three Langevin transducers with different piezoceramic stack locations by characterizing their linear and nonlinear vibrational responses to understand how the stack location influences nonlinear behavior
High-fidelity quantum logic gates using trapped-ion hyperfine qubits
We demonstrate laser-driven two-qubit and single-qubit logic gates with
fidelities 99.9(1)% and 99.9934(3)% respectively, significantly above the
approximately 99% minimum threshold level required for fault-tolerant quantum
computation, using qubits stored in hyperfine ground states of calcium-43 ions
held in a room-temperature trap. We study the speed/fidelity trade-off for the
two-qubit gate, for gate times between 3.8s and 520s, and develop a
theoretical error model which is consistent with the data and which allows us
to identify the principal technical sources of infidelity.Comment: 1 trap, 2 ions, 3 nines. Detailed write-up of arXiv:1406.5473
including single-qubit gate data als
Preliminary Evaluation of Guava (Psidium guajava L.) Tree Branches for Truss Fabrication in Nigeria
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 8 (2006): Preliminary Evaluation of Guava (Psidium guajava L.) Tree Branches for Truss Fabrication in Nigeria. Manuscript BC 05 010. Vol. VIII. May, 2006
A comparison of parametric, semi-nonparametric, adaptive, and nonparametric cointegration tests
This paper provides an extensive Monte-Carlo comparison of severalcontemporary cointegration tests. Apart from the familiar Gaussian basedtests of Johansen, we also consider tests based on non-Gaussianquasi-likelihoods. Moreover, we compare the performance of these parametrictests with tests that estimate the score function from the data using eitherkernel estimation or semi-nonparametric density approximations. Thecomparison is completed with a fully nonparametric cointegration test. Insmall samples, the overall performance of the semi-nonparametric approachappears best in terms of size and power. The main cost of thesemi-nonparametric approach is the increased computation time. In largesamples and for heavily skewed or multimodal distributions, the kernel basedadaptive method dominates. For near-Gaussian distributions, however, thesemi-nonparametric approach is preferable again
Evolution of shell structure in neutron-rich calcium isotopes
We employ interactions from chiral effective field theory and compute the
binding energies and low-lying excitations of calcium isotopes with the
coupled-cluster method. Effects of three-nucleon forces are included
phenomenologically as in-medium two-nucleon interactions, and the coupling to
the particle continuum is taken into account using a Berggren basis. The
computed ground-state energies and the low-lying 2+ states for the isotopes
42,48,50,52Ca are in good agreement with data, and we predict the excitation
energy of the first 2+ state in 54Ca at 1.9 MeV, displaying only a weak
sub-shell closure. In the odd-mass nuclei 53,55,61Ca we find that the positive
parity states deviate strongly from the naive shell model.Comment: 5 pages, 4 figures; small correction of effective 3NF and slight
change of the corresponding parameters; updated figures and tables; main
results and conclusions unchange
Description of stochastic and chaotic series using visibility graphs
Nonlinear time series analysis is an active field of research that studies
the structure of complex signals in order to derive information of the process
that generated those series, for understanding, modeling and forecasting
purposes. In the last years, some methods mapping time series to network
representations have been proposed. The purpose is to investigate on the
properties of the series through graph theoretical tools recently developed in
the core of the celebrated complex network theory. Among some other methods,
the so-called visibility algorithm has received much attention, since it has
been shown that series correlations are captured by the algorithm and
translated in the associated graph, opening the possibility of building
fruitful connections between time series analysis, nonlinear dynamics, and
graph theory. Here we use the horizontal visibility algorithm to characterize
and distinguish between correlated stochastic, uncorrelated and chaotic
processes. We show that in every case the series maps into a graph with
exponential degree distribution P (k) ~ exp(-{\lambda}k), where the value of
{\lambda} characterizes the specific process. The frontier between chaotic and
correlated stochastic processes, {\lambda} = ln(3/2), can be calculated
exactly, and some other analytical developments confirm the results provided by
extensive numerical simulations and (short) experimental time series
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