8,682 research outputs found
Upper Pseudogap Phase: Magnetic Characterizations
It is proposed that the upper pseudogap phase (UPP) observed in the high-Tc
cuprates correspond to the formation of spin singlet pairing under the bosonic
resonating-valence-bond (RVB) description. We present a series of evidence in
support of such a scenario based on the calculated magnetic properties
including uniform spin susceptibility, spin-lattice and spin-echo relaxation
rates, which consistently show that strong spin correlations start to develop
upon entering the UPP, being enhanced around the momentum (\pi, \pi) while
suppressed around (0, 0). The phase diagram in the parameter space of doping
concentration, temperature, and external magnetic field, is obtained based on
the the bosonic RVB theory. In particular, the competition between the Zeeman
splitting and singlet pairing determines a simple relation between the
"critical" magnetic field, H_{PG}, and characteristic temperature scale, T0, of
the UPP. We also discuss the magnetic behavior in the lower pseudogap phase at
a temperature Tv lower than T0, which is characterized by the formation of
Cooper pair amplitude where the low-lying spin fluctuations get suppressed at
both (0, 0) and (\pi, \pi). Properties of the UPP involving charge channels
will be also briefly discussed.Comment: 11 pages, 5 figures, final version to appear in PR
Scattering on two Aharonov-Bohm vortices with opposite fluxes
The scattering of an incident plane wave on two Aharonov-Bohm vortices with
opposite fluxes is considered in detail. The presence of the vortices imposes
non-trivial boundary conditions for the partial waves on a cut joining the two
vortices. These conditions result in an infinite system of equations for
scattering amplitudes between incoming and outgoing partial waves, which can be
solved numerically. The main focus of the paper is the analytic determination
of the scattering amplitude in two limits, the small flux limit and the limit
of small vortex separation. In the latter limit the dominant contribution comes
from the S-wave amplitude. Calculating it, however, still requires solving an
infinite system of equations, which is achieved by the Riemann-Hilbert method.
The results agree well with the numerical calculations
Self-adaptive step fruit fly algorithm optimized support vector regression model for dynamic response prediction of magnetorheological elastomer base isolator
© 2016 Elsevier B.V. Parameter optimization of support vector regression (SVR) plays a challenging role in improving the generalization ability of machine learning. Fruit fly optimization algorithm (FFOA) is a recently developed swarm optimization algorithm for complicated multi-objective optimization problems and is also suitable for optimizing SVR parameters. In this work, parameter optimization in SVR using FFOA is investigated. In view of problems of premature and local optimum in FFOA, an improved FFOA algorithm based on self-adaptive step update strategy (SSFFOA) is presented to obtain the optimal SVR model. Moreover, the proposed method is utilized to characterize magnetorheological elastomer (MRE) base isolator, a typical hysteresis device. In this application, the obtained displacement, velocity and current level are used as SVR inputs while the output is the shear force response of the device. Experimental testing of the isolator with two types of excitations is applied for model performance evaluation. The results demonstrate that the proposed SSFFOA-optimized SVR (SSFFOA_SVR) has perfect generalization ability and more accurate prediction accuracy than other machine learning models, and it is a suitable and effective method to predict the dynamic behaviour of MRE isolator
Study on the Radial Sealing Principles of Scroll Fluid Compressors with Radial Compliant Mechanism
Fluctuations and scaling of inverse participation ratios in random binary resonant composites
We study the statistics of local field distribution solved by the
Green's-function formalism (GFF) [Y. Gu et al., Phys. Rev. B {\bf 59} 12847
(1999)] in the disordered binary resonant composites. For a percolating
network, the inverse participation ratios (IPR) with are illustrated, as
well as the typical local field distributions of localized and extended states.
Numerical calculations indicate that for a definite fraction the
distribution function of IPR has a scale invariant form. It is also shown
the scaling behavior of the ensemble averaged described by the
fractal dimension . To relate the eigenvectors correlations to resonance
level statistics, the axial symmetry between and the spectral
compressibility is obtained.Comment: 7 pages, 6 figures, accepted by Physical Review
Beyond Wigner's isobaric multiplet mass equation: Effect of charge-symmetry-breaking interaction and Coulomb polarization
The quadratic form of the isobaric multiplet mass equation (IMME), which was
originally suggested by Wigner and has been generally regarded as valid, is
seriously questioned by recent high-precision nuclear mass measurements. The
usual resolution to this problem is to add empirically the cubic and quartic
-terms to characterize the deviations from the IMME, but finding the
origin of these terms remains an unsolved difficulty. Based on a strategy
beyond the Wigner's first-order perturbation, we derive explicitly the cubic
and quartic -terms. These terms are shown to be generated by the effective
charge-symmetry breaking and charge-independent breaking interactions in
nuclear medium combined with the Coulomb polarization effect. Calculations for
the - and lower -shells explore a systematical emergence of the cubic
-term, suggesting a general deviation from the original IMME.
Intriguingly, the magnitude of the deviation exhibits an oscillation-like
behavior with mass number, modulated by the shell effect.Comment: 13 pages, 4 figure
Nonlinear and hysteretic modelling of magnetorheological elastomer base isolator using adaptive neuro-fuzzy inference system
Magnetorheological elastomer (MRE) base isolator is a semi-active control device which has currently obtained increasing attention in the field of vibration control of civil structures. However, the inherent nonlinear and hysteretic response of the device is regarded as a challenge aspect for using the smart device to realize the high performance. Therefore, an accurate and robust model is essential to make full use of these unique features for its engineering applications. In this paper, to solve this issue, adaptive neuro-fuzzy inference system (ANFIS) is utilized to characterize the dynamic behavior of the device. In this proposed model, the inputs are historical displacements and applied current of the device while the output is the shear force generated. To validate its forecast performance, the ANFIS model is also compared with some conventional models. Finally, the result verifies that ANFIS has the best perfection ability among existing MRE-based device models
Maximum Likelihood Estimation for Semiparametric Regression Models with Interval-Censored Multi-State Data
Interval-censored multi-state data arise in many studies of chronic diseases,
where the health status of a subject can be characterized by a finite number of
disease states and the transition between any two states is only known to occur
over a broad time interval. We formulate the effects of potentially
time-dependent covariates on multi-state processes through semiparametric
proportional intensity models with random effects. We adopt nonparametric
maximum likelihood estimation (NPMLE) under general interval censoring and
develop a stable expectation-maximization (EM) algorithm. We show that the
resulting parameter estimators are consistent and that the finite-dimensional
components are asymptotically normal with a covariance matrix that attains the
semiparametric efficiency bound and can be consistently estimated through
profile likelihood. In addition, we demonstrate through extensive simulation
studies that the proposed numerical and inferential procedures perform well in
realistic settings. Finally, we provide an application to a major epidemiologic
cohort study.Comment: 49 page
Motor Imagery Classification Based on Bilinear Sub-Manifold Learning of Symmetric Positive-Definite Matrices
In motor imagery brain-computer interfaces (BCIs), the symmetric positive-definite (SPD) covariance matrices of electroencephalogram (EEG) signals carry important discriminative information. In this paper, we intend to classify motor imagery EEG signals by exploiting the fact that the space of SPD matrices endowed with Riemannian distance is a high-dimensional Riemannian manifold. To alleviate the overfitting and heavy computation problems associated with conventional classification methods on high-dimensional manifold, we propose a framework for intrinsic sub-manifold learning from a high-dimensional Riemannian manifold. Considering a special case of SPD space, a simple yet efficient bilinear sub-manifold learning (BSML) algorithm is derived to learn the intrinsic sub-manifold by identifying a bilinear mapping that maximizes the preservation of the local geometry and global structure of the original manifold. Two BSML-based classification algorithms are further proposed to classify the data on a learned intrinsic sub-manifold. Experimental evaluation of the classification of EEG revealed that the BSML method extracts the intrinsic sub-manifold approximately 5× faster and with higher classification accuracy compared with competing algorithms. The BSML also exhibited strong robustness against a small training dataset, which often occurs in BCI studies
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