14,679 research outputs found
GA tuning of pitch controller for small scale MAVs
The paper presents the application of intelligent tuning methods for the control of a prototype MAV in order to address problems associated with bandwidth limited actuators and gust alleviation. Specifically, as a proof of concept, the investigation is focused on the pitch control of a MAV. The work is supported by experimental results from wind tunnel testing that shows the merits of the use of Genetic Algorithm (GA) tuning techniques compared to classical, empirical tuning methodologies. To provide a measure of relative merit, the controller responses are evaluated using the ITAE performance index. In this way, the proposed method is shown to induce far superior dynamic performance compared to traditional approaches
Spin gap behavior in CuScGeO by Sc nuclear magnetic resonance
We report the results of a Sc nuclear magnetic resonance (NMR) study
on the quasi-one-dimensional compound CuScGeO at
temperatures between 4 and 300 K. This material has been a subject of current
interest due to indications of spin gap behavior. The temperature-dependent NMR
shift exhibits a character of low-dimensional magnetism with a negative broad
maximum at 170 K. Below , the NMR shifts and
spin lattice relaxation rates clearly indicate activated responses, confirming
the existence of a spin gap in CuScGe% O. The experimental
NMR data can be well fitted to the spin dimer model, yielding a spin gap value
of about 275 K which is close to the 25 meV peak found in the inelastic neutron
scattering measurement. A detailed analysis further points out that the nearly
isolated dimer picture is proper for the understanding of spin gap nature in
CuScGeO.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Low-momentum nucleon-nucleon interaction and shell-model calculations
We discuss the use of the low-momentum nucleon-nucleon NN interaction V-low-k
in the derivation of the shell-model effective interaction and emphasize its
practical value as an alternative to the Brueckner G-matrix method. We present
some selected results of our current study of exotic nuclei around closed
shells, which have been obtained starting from the CD-Bonn potential. We also
show some results of calculations performed with different phase-shift
equivalent NN potentials, and discuss the effect of changes in the cutoff
momentum which defines the V-low-k potential.Comment: 5 pages, 5 figures, 1 table, Talk presented at CDN05, 31 Jan - 4 Feb
2005, University of Tokyo, Japa
Demonstration of acoustic waveguiding and tight bending in phononic crystals
Citation: Baboly, M. G., Raza, A., Brady, J., Reinke, C. M., Leseman, Z. C., & El-Kady, I. (2016). Demonstration of acoustic waveguiding and tight bending in phononic crystals. Applied Physics Letters, 109(18), 4. doi:10.1063/1.4966463The systematic design, fabrication, and characterization of an isolated, single-mode, 90 degrees bend phononic crystal (PnC) waveguide are presented. A PnC consisting of a 2D square array of circular air holes in an aluminum substrate is used, and waveguides are created by introducing a line defect in the PnC lattice. A high transmission coefficient is observed (-1 dB) for the straight sections of the waveguide, and an overall 2.3 dB transmission loss is observed (a transmission coefficient of 76%) for the 90 degrees bend. Further optimization of the structure may yield higher transmission efficiencies. This manuscript shows the complete design process for an engineered 90 degrees bend PnC waveguide from inception to experimental demonstration. Published by AIP Publishing
Probing neutrino mass hierarchies and with supernova neutrinos
We investigate the feasibility of probing the neutrino mass hierarchy and the
mixing angle with the neutrino burst from a future supernova. An
inverse power-law density with varying is adopted in the
analysis as the density profile of a typical core-collapse supernova. The
survival probabilities of and are shown to reduce to
two-dimensional functions of and . It is found that in the
parameter space, the 3D plots of the probability
functions exhibit highly non-trivial structures that are sensitive to the mass
hierarchy, the mixing angle , and the value of . The conditions
that lead to observable differences in the 3D plots are established. With the
uncertainty of considered, a qualitative analysis of the Earth matter
effect is also included.Comment: 16 pages, 3 figures. Ref [11] added, and some typos correcte
Primordial Gravitational Waves Enhancement
We reconsider the enhancement of primordial gravitational waves that arises
from a quantum gravitational model of inflation. A distinctive feature of this
model is that the end of inflation witnesses a brief phase during which the
Hubble parameter oscillates in sign, changing the usual Hubble friction to
anti-friction. An earlier analysis of this model was based on numerically
evolving the graviton mode functions after guessing their initial conditions
near the end of inflation. The current study is based on an equation which
directly evolves the normalized square of the magnitude. We are also able to
make a very reliable estimate for the initial condition using a rapidly
converging expansion for the sub-horizon regime. Results are obtained for the
energy density per logarithmic wave number as a fraction of the critical
density. These results exhibit how the enhanced signal depends upon the number
of oscillatory periods; they also show the resonant effects associated with
particular wave numbers.Comment: 25 pages, 14 figure
Supernova neutrinos in the light of FCNC
We study the effect of including flavor changing neutral currents (FCNC) in
the analysis of the neutrino signal of a supernova burst. When we include the
effect of the FCNC which are beyond the standard model (SM) in the study of the
MSW resonant conversion, we obtain dramatic changes in the \Delta
m^2-sin^2(2\theta) probability contours for neutrino detection.Comment: 8 pages in ReVTeX,3 figures. Revised manuscript submitted to Phys.
Rev.
Possible Enhancement of High Frequency Gravitational Waves
We study the tensor perturbations in a class of non-local, purely
gravitational models which naturally end inflation in a distinctive phase of
oscillations with slight and short violations of the weak energy condition. We
find the usual generic form for the tensor power spectrum. The presence of the
oscillatory phase leads to an enhancement of gravitational waves with
frequencies somewhat less than 10^{10} Hz.Comment: 27 pages, 11 figures, LaTeX.2
Nodeless superconductivity in the cage-type superconductor Sc5Ru6Sn18 with preserved time-reversal symmetry
We report the single-crystal synthesis and detailed investigations of the
cage-type superconductor Sc5Ru6Sn18, using powder x-ray diffraction (XRD),
magnetization, specific-heat and muon-spin relaxation (muSR) measurements.
Sc5Ru6Sn18 crystallizes in a tetragonal structure (space group I41/acd) with
the lattice parameters a = 1.387(3) nm and c = 2.641(5) nm. Both DC and AC
magnetization measurements prove the type-II superconductivity in Sc5Ru6Sn18
with Tc = 3.5(1) K, a lower critical field H_c1 (0) = 157(9) Oe and an upper
critical field, H_c2 (0) = 26(1) kOe. The zero-field electronic specific-heat
data are well fitted using a single-gap BCS model, with superconducting gap =
0.64(1) meV. The Sommerfeld constant varies linearly with the applied magnetic
field, indicating s-wave superconductivity in Sc5Ru6Sn18. Specific-heat and
transverse-field (TF) muSR measurements reveal that Sc5Ru6Sn18 is a
superconductor with strong electron-phonon coupling, with TF-muSR also
suggesting the single-gap s-wave character of the superconductivity.
Furthermore, zero-field muSR measurements do not detect spontaneous magnetic
fields below Tc, hence implying that time-reversal symmetry is preserved in
Sc5Ru6Sn18.Comment: 23 pages, 11 figure
Variational Principle for Mixed Classical-Quantum Systems
An extended variational principle providing the equations of motion for a
system consisting of interacting classical, quasiclassical and quantum
components is presented, and applied to the model of bilinear coupling. The
relevant dynamical variables are expressed in the form of a quantum state
vector which includes the action of the classical subsystem in its phase
factor. It is shown that the statistical ensemble of Brownian state vectors for
a quantum particle in a classical thermal environment can be described by a
density matrix evolving according to a nonlinear quantum Fokker-Planck
equation. Exact solutions of this equation are obtained for a two-level system
in the limit of high temperatures, considering both stationary and
nonstationary initial states. A treatment of the common time shared by the
quantum system and its classical environment, as a collective variable rather
than as a parameter, is presented in the Appendix.Comment: 16 pages, LaTex; added Figure 2 and Figure
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