Agility radar with the carrier frequency random hopping and the pulse repetition frequency (PRF) staggering from pulse to pulse achieves superior performance against the electromagnetic jamming. This ...novel scheme leads to the discontinuity of phase in a coherent processing interval, thus the fast Fourier transform-based method is no longer a valid way to estimate the velocity of a target. A novel sparse optimisation method based on compressed sensing is proposed for high-resolution range–Doppler reconstruction from random frequency hopping and PRF-jittering pulses. The performance of moving target detection of the proposed method for frequency agile and PRF-jittering radar is analysed by comparing it with parameters-fixed pulse Doppler radar. Both simulation and field experimental results demonstrate the effectiveness of the proposal.
Focusing moving targets with frequency-domain algorithms may suffer from azimuth spectrum not entirely contained within a pulse-repetition frequency band, which may lead to degraded detection ...performance due to distributing the energy to the artifacts. In order to avoid this problem, a refocusing algorithm after back-projection integral is proposed. The main idea is first to uniformly and coarsely focus moving targets for detection, and then extract the detected targets for refocusing. By deriving the exact analytic expression of the wavenumber spectrum, motion parameter estimation and motion compensation are directly carried out on the 2-D wavenumber domain of the small-sized extracted data, which involves fast Fourier transform and Inverse Fast Fourier Transform operations only with no interpolation, thus reduces the computational complexity. Then, the final refocused image of the moving target is achieved. Refocusing results of both airborne and spaceborne synthetic aperture radar data are shown to validate the effectiveness of the proposed method.
In a short observation time, after the range alignment and phase adjustment, the motion of a target can be approximated as a uniform rotation. The radar observing process can be simply described as ...multiplying an observation matrix on the ISAR image, which can be thought of as a linear system. It is known that the longer observation time is, the higher cross-range resolution is. In order to deal with the conflict between short observation time and high cross-range resolution, we introduce Kalman filtering (KF) into the ISAR imaging and propose a novel method to reconstruct a high-resolution image with short time observed data. As KF has excellent reconstruction performance, it leads to a good application in ISAR image reconstruction. At each observation aperture, the reconstructed image denotes the state vector in KF at the aperture time. It is corrected by a two-step KF process: prediction and update. As iteration continues, the state vector is gradually corrected to a well-focused high-resolution image. Thus, the proposed method can obtain a high-resolution image in a short observation time. Both simulated and real data are applied to demonstrate the performance of the proposed method.
Phononic crystals that prevent the propagation of waves in a band gap have been widely applied in wave propagation control. In this paper, we propose the use of a metabarrier, based on a locally ...resonant phononic crystal mechanism, as a floating-slab track bearing to shield the infrastructure in a floating-slab track system from longitudinal waves from the slab, thereby improving mitigation of ground-borne vibrations. The locally resonant band gap properties of the metabarrier were studied based on the finite element method, and the shielding performance was verified by the transmission spectrum. Simplified models for band gap boundary frequencies were built according to the wave modes. Furthermore, a 3D half-track model was built to investigate the overall vibration mitigation performance of the floating-slab track with the metabarrier. An optimization mechanism for the band gap boundary frequencies is proposed. As the low-frequency ground-borne vibrations induced by subways carry the most energy, multi-objective genetic algorithm optimization was conducted to obtain a lower and wider band gap for a better shielding performance. The results show that the retained vibration isolation performance of the low natural frequency, the shielding performance of the band gap, and the controllability of band gap boundary frequencies all contribute to an improvement in overall vibration mitigation performance. The vertical static stiffness of the metabarrier was close to that of the existing bearing of the floating-slab track. An optimized locally resonant band gap from 50 to 113 Hz was generated using the optimization mechanism.
For a multiple-input and multiple-output synthetic aperture radar, stepped frequency chirps can be used to generate high-resolution range profiles (HRRPs) by using spectrum synthesis. However, the ...presence of channel phase errors may degrade the performance of HRRP synthesis. This letter presents a channel error estimation method to address this problem. First, to obtain a focused subband image, a range phase adjustment by contrast enhancement algorithm is proposed to estimate inner-channel high-order phase errors. Second, a sidelobe balanced model is established to estimate constant phase error from the relationship between the balanced sidelobe and constant phase; the constant phase error can be directly obtained in an efficient manner. Experimental analysis using real data demonstrates the effectiveness of the proposed method.
BACKGROUNDAs the main component of oral contraceptives (OCs), ethinylestradiol (EE) has been widely applied as a model drug to induce murine intrahepatic cholestasis. The clinical counterpart of ...EE-induced cholestasis includes women who are taking OCs, sex hormone replacement therapy, and susceptible pregnant women. Taking intrahepatic cholestasis of pregnancy (ICP) as an example, ICP consumes the medical system due to its high-risk fetal burden and the impotency of ursodeoxycholic acid in reducing adverse perinatal outcomes. AIMTo explore the mechanisms and therapeutic strategies of EE-induced cholestasis based on the liver immune microenvironment. METHODSMale C57BL/6J mice or invariant natural killer T (iNKT) cell deficiency (Jα18-/- mice) were administered with EE (10 mg/kg, subcutaneous) for 14 d. RESULTSBoth Th1 and Th2 cytokines produced by NKT cells increased in the liver skewing toward a Th1 bias. The expression of the chemokine/chemokine receptor Cxcr6/Cxcl16, toll-like receptors, Ras/Rad, and PI3K/Bad signaling was upregulated after EE administration. EE also influenced bile acid synthase Cyp7a1, Cyp8b1, and tight junctions ZO-1 and Occludin, which might be associated with EE-induced cholestasis. iNKT cell deficiency (Jα18-/- mice) robustly alleviated cholestatic liver damage and lowered the expression of the abovementioned signaling pathways. CONCLUSIONHepatic NKT cells play a pathogenic role in EE-induced intrahepatic cholestasis. Our research improves the understanding of intrahepatic cholestasis by revealing the hepatic immune microenvironment and also provides a potential clinical treatment by regulating iNKT cells.
In this paper, for a multichannel synthetic aperture radar-ground moving target indication (SAR-GMTI) system, a new high-accuracy focusing and relocating method using instantaneous interferometry, ...i.e., carrying out interferometry operation in the azimuth time domain before focusing, is proposed. One of the key steps of this method is to perform instantaneous interferometry to get accurate equivalent cross-track velocity (ECV) estimation for cross-track motion compensation. After that, the signal from a moving target is concentrated in range, and along-track motion compensation becomes convenient. Motion compensation transforms a moving target into a stationary one; thus, the conventional SAR imaging algorithm can be applied to focus the moving target. Finally, a strategy for accurately relocating a moving target is presented. The processing results of simulated and measured data illustrate the effectiveness of the proposed method.
An experimental study and theoretical analysis were carried out to explore the ground-borne vibration generated by elevated high-speed railway in rock strata. Taking a typical rail line constructed ...on rock area in China as the research object, a set of field tests was performed on Rizhao-Lankao High-Speed Railway, the bridge and ground vibrations were measured as trains passed at 330–340 km/h, then the transferring law and spatial distribution under individual frequencies were investigated. The experiment results indicate that the bridge frequency spectrum exhibited relatively high-frequency vibration peaks caused by short-wavelength irregularity; ground vibration farther than 30 m away can be amplified with a higher frequency and numerous components. Furthermore, the wave propagation equation of a stratified rock strata was established based on direct-stiffness method to explore the vibration attenuation rules via frequency-domain analysis. It is found that the rock area has a weaker correlation between vibration transmissibility and frequency, thicker and harder rock strata loss their vibration attenuation capacity. It can be concluded that the high-speed railways induced vibration on rock strata shows a wide frequency band and large amplitude, the design of reducing vibration aimed at specific frequency is important according to next more detailed numerical study.
Excessive vibration and noise radiation of the track structure can be caused by the operation of high speed trains. Though the track structure is characterized by obvious periodic properties and band ...gaps, the bandwidth is narrow and the elastic wave attenuation capability within the band gap is weak. In order to effectively control the vibration and noise of track structure, the local resonance mechanism is introduced to broaden the band gap and realize wave propagation control. The locally resonant units are attached periodically on the rail, forming a new locally resonant phononic crystal structure. Then the tuning of the elastic wave band gaps of track structure is discussed, and the formation mechanism of the band gap is explicated. The research results show that a new wide and adjustable locally resonant band gap is formed after the resonant units are introduced. The phenomenon of coupling and transition can be observed between the new locally resonant band gap and the original band gap of the periodic track structure with the band gap width reaching the maximum at the coupling position. The broader band gap can be applied for vibration and noise reduction in high speed railway track structure.
In this work, we investigated the anaerobic decolorization of methyl orange (MO), a typical azo dye, by
Shewanella oneidensis
MR-1, which can use various organic and inorganic substances as its ...electron acceptor in natural and engineered environments.
S. oneidensis
MR-1 was found to be able to obtain energy for growth through anaerobic respiration accompanied with dissimilatory azo-reduction of MO. Chemical analysis shows that MO reduction occurred via the cleavage of azo bond. Block of Mtr respiratory pathway, a transmembrane electron transport chain, resulted in a reduction of decolorization rate by 80%, compared to the wild type. Knockout of
cymA
resulted in a substantial loss of its azo-reduction ability, indicating that CymA is a key
c
-type cytochrome in the electron transfer chain to MO. Thus, the MtrA-MtrB-MtrC respiratory pathway is proposed to be mainly responsible for the anaerobic decolorization of azo dyes such as MO by
S. oneidensis
.
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