6,545 research outputs found
Development of the inventory management system into scientificproduction enterprise “Alliyans”
Symmetry protection of topological order in one-dimensional quantum spin systems
We discuss the characterization and stability of the Haldane phase in integer
spin chains on the basis of simple, physical arguments. We find that an odd-
Haldane phase is a topologically non-trivial phase which is protected by any
one of the following three global symmetries: (i) the dihedral group of
-rotations about and axes; (ii) time-reversal symmetry
; (iii) link inversion symmetry (reflection
about a bond center), consistently with previous results [Phys. Rev. B
\textbf{81}, 064439 (2010)]. On the other hand, an even- Haldane phase is
not topologically protected (i.e., it is indistinct from a trivial,
site-factorizable phase). We show some numerical evidence that supports these
claims, using concrete examples.Comment: 9 pages, 6 figures, extended version: several new examples and
numerical results added. Journal reference adde
Sequentially generated states for the study of two dimensional systems
Matrix Product States can be defined as the family of quantum states that can
be sequentially generated in a one-dimensional system. We introduce a new
family of states which extends this definition to two dimensions. Like in
Matrix Product States, expectation values of few body observables can be
efficiently evaluated and, for the case of translationally invariant systems,
the correlation functions decay exponentially with the distance. We show that
such states are a subclass of Projected Entangled Pair States and investigate
their suitability for approximating the ground states of local Hamiltonians.Comment: 10 pages, 4 figure
Using Multiple Fidelity Numerical Models for Floating Offshore Wind Turbine Advanced Control Design
This paper summarises the tuning process of the Aerodynamic Platform Stabiliser control loop and its performance with Floating Offshore Wind Turbine model. Simplified Low-Order Wind turbine numerical models have been used for the system identification and control tuning process. Denmark Technical University's 10 MW wind turbine model mounted on the TripleSpar platform concept was used for this study. Time-domain simulations were carried out in a fully coupled non-linear aero-hydro-elastic simulation tool FAST, in which wind and wave disturbances were modelled. This testing yielded significant improvements in the overall Floating Offshore Wind Turbine performance and load reduction, validating the control technique presented in this work.This work was partially funded by the Spanish Ministry of Economy and Competitiveness through the research project DPI2017-82930-C2-2-R
Real-time phasefront detector for heterodyne interferometers
We present a real-time differential phasefront detector sensitive to better
than 3 mrad rms, which corresponds to a precision of about 500 pm. This
detector performs a spatially resolving measurement of the phasefront of a
heterodyne interferometer, with heterodyne frequencies up to approximately 10
kHz. This instrument was developed as part of the research for the LISA
Technology Package (LTP) interferometer, and will assist in the manufacture of
its flight model. Due to the advantages this instrument offers, it also has
general applications in optical metrology
Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings
Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer ReviewedPostprint (author's final draft
Weak branch and multimodal convection in rapidly rotating spheres at low Prandtl number
The focus of this study is to investigate primary and secondary bifurcations to weakly nonlinear flows (weak branch) in convective rotating spheres in a regime where only strongly nonlinear oscillatory sub- and supercritical flows (strong branch) were previously found [E. J. Kaplan, N. Schaeffer, J. Vidal, and P. Cardin, Phys. Rev. Lett. 119, 094501 (2017)]. The relevant regime corresponds to low Prandtl and Ekman numbers, indicating a predominance of Coriolis forces and thermal diffusion in the system. We provide the bifurcation diagrams for rotating waves (RWs) computed by means of continuation methods and the corresponding stability analysis of these periodic flows to detect secondary bifurcations giving rise to quasiperiodic modulated rotating waves (MRWs). Additional direct numerical simulations (DNS) are performed for the analysis of these quasiperiodic flows for which Poincaré sections and kinetic energy spectra are presented. The diffusion timescales are investigated as well. Our study reveals very large initial transients (more than 30 diffusion time units) for the nonlinear saturation of solutions on the weak branch, either RWs or MRWs, when DNS are employed. In addition, we demonstrate that MRWs have multimodal nature involving resonant triads. The modes can be located in the bulk of the fluid or attached to the outer sphere and exhibit multicellular structures. The different resonant modes forming the nonlinear quasiperiodic flows can be predicted with the stability analysis of RWs, close to the Hopf bifurcation point, by analyzing the leading unstable Floquet eigenmode.Peer ReviewedPostprint (author's final draft
3-D Photoionization Structure and Distances of Planetary Nebulae IV. NGC 40
Continuing our series of papers on the 3-D structure and accurate distances
of Planetary Nebulae (PNe), we present here the results obtained for the
planetary nebula NGC\,40. Using data from different sources and wavelengths, we
construct 3-D photoionization models and derive the physical quantitities of
the ionizing source and nebular gas. The procedure, discussed in detail in the
previous papers, consists of the use of 3-D photoionization codes constrained
by observational data to derive the three-dimensional nebular structure,
physical and chemical characteristics and ionizing star parameters of the
objects by simultaneously fitting the integrated line intensities, the density
map, the temperature map, and the observed morphologies in different emission
lines. For this particular case we combined hydrodynamical simulations with the
photoionization scheme in order to obtain self-consistent distributions of
density and velocity of the nebular material. Combining the velocity field with
the emission line cubes we also obtained the synthetic position-velocity plots
that are compared to the observations. Finally, using theoretical evolutionary
tracks of intermediate and low mass stars, we derive the mass and age of the
central star of NGC\,40 as M and yrs, respectively. The distance obtained from the fitting procedure was
pc.Comment: 12 pages, 11 figures, accepted for publication in Ap
First higher-multipole model of gravitational waves from spinning and coalescing black-hole binaries
Gravitational-wave observations of binary black holes currently rely on
theoretical models that predict the dominant multipoles (l,m) of the radiation
during inspiral, merger and ringdown. We introduce a simple method to include
the subdominant multipoles to binary black hole gravitational waveforms, given
a frequency-domain model for the dominant multipoles. The amplitude and phase
of the original model are appropriately stretched and rescaled using
post-Newtonian results (for the inspiral), perturbation theory (for the
ringdown), and a smooth transition between the two. No additional tuning to
numerical-relativity simulations is required. We apply a variant of this method
to the non-precessing PhenomD model. The result, PhenomHM, constitutes the
first higher-multipole model of spinning black-hole binaries, and currently
includes the (l,m) = (2,2), (3,3), (4,4), (2,1), (3,2), (4,3) radiative
moments. Comparisons with numerical-relativity waveforms demonstrate that
PhenomHM is more accurate than dominant-multipole-only models for all binary
configurations, and typically improves the measurement of binary properties.Comment: 4 pages, 4 figure
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