2,437 research outputs found
Orbital-transverse density-wave instabilities in iron-based superconductors
Besides the conventional spin-density-wave (SDW) state, a new kind of
orbital-transverse density-wave (OTDW) state is shown to exist generally in
multi-orbital systems. We demonstrate that the orbital character of Fermi
surface nesting plays an important role in density responses. The relationship
between antiferromagnetism and structural phase transition in LaFeAsO (1111)
and BaFeAs (122) compounds of iron-based superconductors may be
understood in terms of the interplay between the SDW and OTDW with a
five-orbital Hamiltonian. We propose that the essential difference between 1111
and 122 compounds is crucially determined by the presence of the
two-dimensional -like Fermi surface around (0,0) being only in 1111
parent compounds.Comment: several parts were rewritten for clarity. 6 pages, 3 figures, 1 tabl
Enhanced transmission of optically thick metallic films at infrared wavelengths
For an optically thick metallic film, the transmission for both s- and
p-polarized waves is extremely low. If the metallic film is coated on both
sides with a finite dielectric layer, light transmission for -polarized
waves can be enhanced considerably. This enhancement is not related to surface
plasmon-polaritions. Instead, it is due to the interplay between Fabry-Perot
interference in the coated dielectric layer and the existence of the Brewster
angle at the dielectric/metallic interface. It is shown that the coated
metallic films can act as excellent polarizers at infrared wavelengths.Comment: 3 pages, 4 figures. Submitted to Appl. Phys. Let
Non-Hermitian Stark Many-Body Localization
Utilizing exact diagonalization (ED) techniques, we investigate a
one-dimensional, non-reciprocal, interacting hard-core boson model under a
Stark potential with tail curvature. By employing the non-zero imaginary
eigenenergies ratio, half-chain entanglement entropy, and eigenstate
instability, we numerically confirm that the critical points of spectral
real-complex (RC) transition and many-body localization (MBL) phase transition
are not identical, and an examination of the phase diagrams reveals that the
spectral RC transition arises before the MBL phase transition, which suggests
the existence of a novel non-MBL-driven spectral RC transition. These findings
are quite unexpected, and they are entirely different from observations in
disorder-driven interacting non-Hermitian systems. This work provides a useful
reference for further research on phase transitions in disorder-free
interacting non-Hermitian systems.Comment: Any comments or suggestions are welcome
The study on magnetism and solid coupling vibration and its electromagnetic force characteristics in stator system of electrical machine
The air-gap electromagnetic force is not the unique excitation which excites magnetism and solid coupling vibration on stator system of asynchronous machine. Besides, there should be a ponderomotive force as an internal electromagnetic excitation in stator core. Therefore, the magnetism and solid coupling vibration equation with both of the forces was obtained for the electromagnetically excited vibration on stator system of electrical machine. Based on Maxwell equations and the electromagnetic constitutive relation, the expressions of the electromagnetic field and force were derived by solving the eddy equation and the boundary conditions. With numerical calculation, the influences of geometric parameters on the electromagnetic field and forces were analyzed. The electromagnetic excitations of magnetism and solid coupling vibration on stator system were improved by the analysis of ponderomotive force in the stator core. Furthermore, the conclusions provide a theoretical basis for the electromagnetic design of asynchronous machine
Step-by-step random walk network with power-law clique-degree distribution
We propose a simple mechanism for generating scale-free networks with degree exponent γ = 3, where the new node is connected to the existing nodes by step-by-step random walk. It is found that the clique-degree distribution based on our model obeys a power-law form, which is in agreement with the recently empirical evidences. In addition, our model displays the small-world effect and the hierarchical structure
Fault diagnosis for rotating machinery based on multi-differential empirical mode decomposition
The fault diagnosis of rotating machinery has crucial significance for the safety of modern industry, and the fault feature extraction is the key link of the diagnosis process. As an effective time-frequency method, Empirical Mode Decomposition (EMD) has been widely used in signal processing and feature extraction. However, the mode mixing phenomenon may lead to confusion in the identification of multi frequency signals and restricts the applications of EMD. In this paper, a novel method based on Multi-Differential Empirical Mode Decomposition (MDEMD) was proposed to extract the energy distribution characteristics of fault signals. Firstly, multi-order differential signals were deduced and decomposed by EMD. Then, their energy distribution characteristics were extracted and utilized to construct the feature matrix. Finally, taking the feature matrix as input, the classifiers were applied to diagnosis the existence and severity of rotating machinery faults. Simulative and practical experiments were implemented respectively, and the results demonstrated that the proposed method, i.e. MDEMD, is able to eliminate the mode mixing effectively, and the feature matrix extracted by MDEMD has high separability and universality, furthermore, the fault diagnosis based on MDEMD can be accomplished more effectively and efficiently with satisfactory accuracy
Classification of Diabetic Foot Ulcers Using Class Knowledge Banks
Diabetic foot ulcers (DFUs) are one of the most common complications of diabetes. Identifying the presence of infection and ischemia in DFU is important for ulcer examination and treatment planning. Recently, the computerized classification of infection and ischaemia of DFU based on deep learning methods has shown promising performance. Most state-of-the-art DFU image classification methods employ deep neural networks, especially convolutional neural networks, to extract discriminative features, and predict class probabilities from the extracted features by fully connected neural networks. In the testing, the prediction depends on an individual input image and trained parameters, where knowledge in the training data is not explicitly utilized. To better utilize the knowledge in the training data, we propose class knowledge banks (CKBs) consisting of trainable units that can effectively extract and represent class knowledge. Each unit in a CKB is used to compute similarity with a representation extracted from an input image. The averaged similarity between units in the CKB and the representation can be regarded as the logit of the considered input. In this way, the prediction depends not only on input images and trained parameters in networks but the class knowledge extracted from the training data and stored in the CKBs. Experimental results show that the proposed method can effectively improve the performance of DFU infection and ischaemia classifications
Colorectal cancer screening with fecal occult blood test: A 22-year cohort study.
The aim of the present study was to investigate the efficacy of colorectal cancer (CRC) screening with a three-tier fecal occult blood test (FOBT) in the Chinese population. The study was performed between 1987 and 2008 at the Beijing Military General Hospital, in a cohort of army service males and females aged >50 years. Between 1987 and 2005, a three-tier screening program, comprising guaiac-based FOBTs (gFOBTs), followed by immunochemical FOBTs for positive guaiac test samples and then colonoscopy for positive immunochemical test subjects, was performed annually. The cohort was followed up until 2008. The cohort included 5,104 subjects, of which, 3,863 subjects participated in screening (screening group) and 1,241 did not (non-screening group). The two groups did not differ in age, gender or other major risk factors for colon cancer. Overall, 36 CRCs occurred in the screening group and 21 in the non-screening group. Compared with the non-screening group, the relative risk for the incidence and mortality of CRC was 0.51 [95% confidence interval (CI), 0.30-0.87] and 0.36 (95% CI, 0.18-0.71), respectively, in the screening group. The general sensitivity of this three-tier FOBT was 80.6% (95% CI, 65.3-91.1). Thus, annual screening using the three-tier FOBT program may reduce the CRC incidence and mortality rate
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