7,748 research outputs found

    Redshift drift exploration for interacting dark energy

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    By detecting redshift drift in the spectra of Lyman-α\alpha forest of distant quasars, Sandage-Loeb (SL) test directly measures the expansion of the universe, covering the "redshift desert" of 2z52 \lesssim z \lesssim5. Thus this method is definitely an important supplement to the other geometric measurements and will play a crucial role in cosmological constraints. In this paper, we quantify the ability of SL test signal by a CODEX-like spectrograph for constraining interacting dark energy. Four typical interacting dark energy models are considered: (i) Q=γHρcQ=\gamma H\rho_c, (ii) Q=γHρdeQ=\gamma H\rho_{de}, (iii) Q=γH0ρcQ=\gamma H_0\rho_c, and (iv) Q=γH0ρdeQ=\gamma H_0\rho_{de}. The results show that for all the considered interacting dark energy models, relative to the current joint SN+BAO+CMB+H0H_0 observations, the constraints on Ωm\Omega_m and H0H_0 would be improved by about 60\% and 30--40\%, while the constraints on ww and γ\gamma would be slightly improved, with a 30-yr observation of SL test. We also explore the impact of SL test on future joint geometric observations. In this analysis, we take the model with Q=γHρcQ=\gamma H\rho_c as an example, and simulate future SN and BAO data based on the space-based project WFIRST. We find that in the future geometric constraints, the redshift drift observations would help break the geometric degeneracies in a meaningful way, thus the measurement precisions of Ωm\Omega_m, H0H_0, ww, and γ\gamma could be substantially improved using future probes.Comment: 6 pages, 5 figures; accepted for publication in EPJC. arXiv admin note: text overlap with arXiv:1407.712

    Fault Diagnosis of Train Axle Box Bearing Based on Multifeature Parameters

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    Failure of the train axle box bearing will cause great loss. Now, condition-based maintenance of train axle box bearing has been a research hotspot around the world. Vibration signals generated by train axle box bearing have nonlinear and nonstationary characteristics. The methods used in traditional bearing fault diagnosis do not work well with the train axle box. To solve this problem, an effective method of axle box bearing fault diagnosis based on multifeature parameters is presented in this paper. This method can be divided into three parts, namely, weak fault signal extraction, feature extraction, and fault recognition. In the first part, a db4 wavelet is employed for denoising the original signals from the vibration sensors. In the second part, five time-domain parameters, five IMF energy-torque features, and two amplitude-ratio features are extracted. The latter seven frequency domain features are calculated based on the empirical mode decomposition and envelope spectrum analysis. In the third part, a fault classifier based on BP neural network is designed for automatic fault pattern recognition. A series of tests are carried out to verify the proposed method, which show that the accuracy is above 90%

    Electrocardiogram Baseline Wander Suppression Based on the Combination of Morphological and Wavelet Transformation Based Filtering

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    One of the major noise components in electrocardiogram (ECG) is the baseline wander (BW). Effective methods for suppressing BW include the wavelet-based (WT) and the mathematical morphological filtering-based (MMF)algorithms. However, the T waveform distortions introduced by the WTand the rectangular/trapezoidal distortions introduced by MMF degrade the quality of the output signal. Hence, in this study, we introduce a method by combining the MMF and WTto overcome the shortcomings of both existing methods. To demonstrate the effectiveness of the proposed method, artificial ECG signals containing a clinicalBW are used for numerical simulation, and we also create a realistic model of baseline wander to compare the proposed method with other state-of-the-art methods commonly used in the literature. /e results show that the BW suppression effect of the proposed method is better than that of the others. Also, the new method is capable of preserving the outline of the BW and avoiding waveform distortions caused by the morphology filter, thereby obtaining an enhanced quality of ECG

    A study of vortex ring generation by a circular disc

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    A vortex ring is a region where the fluid mostly spins around an imaginary axis line that forms a closed loop. It is a fundamental phenomenon for the fluid passing by an object. In general, there are two methods associated with the axisymmetric vortex generation: fluid discharge from an orifice or a nozzle, and disc start-up instantly. Recent study by Yang (2012) showed that the different mechanisms of vortex generation could lead to a similar formation process and a universal principle of the optimal vortex formation could exist. Present work is mainly based on a numerical simulation study of disc vortex ring formation. A commercial Computational Fluid Dynamics solver is employed to carry out the simulation. The simulation parameters are selected the same as those of Yang’s (2012) experimental study. The model is built with fluid passing by a 30mm diameter and 2mm thickness disc in a large computational domain. The simulation results are validated with experimental data. By studying the Iso-surface, representative values, i.e. size of both vortex ring and vortex ring core, circulation and kinetic energy during the formation phases of the vortex ring are investigated. Comparison and analyses between the numerical simulation and the experimental data will be given in detail
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