Deblending based on the frequency-structure weighted threshold: The case of the slope-constrained f-k transform

In the process of separating blended data, conventional methods based on sparse inversion assume that the primary source is coherent and the secondary source is randomized. The L1-norm, the commonly used regularization term, uses a global threshold to process the sparse spectrum in the transform domain; however, when the threshold is relatively high, more high-frequency information from the primary source will be lost. For this reason, we analyze the generation principle of blended data based on the convolution theory and then conclude that the blended data is only randomly distributed in the spatial domain. Taking the slope-constrained frequency-wavenumber ( f- k) transform as an example, we propose a frequency-dependent threshold, which reduces the high-frequency loss during the deblending process. Then we propose to use a structure weighted threshold in which the energy from the primary source is concentrated along the wavenumber direction. The combination of frequency and structure-weighted thresholds effectively improves the deblending performance. Model and field data show that the proposed frequency-structure weighted threshold has better frequency preservation than the global threshold. The weighted threshold can better retain the high-frequency information of the primary source, and the similarity between other frequency-band data and the unblended data has been improved.

Scintillation Timescales of Bright FRBs Detected by CHIME/FRB

We describe a pipeline to measure scintillation in fast radio bursts (FRBs) detected by CHIME/FRB in the 400–800 MHz band by analyzing the frequency structure of the FRB's spectrum. We use the pipeline to measure the characteristic frequency bandwidths of scintillation between 4–100 kHz in 12 FRBs corresponding to timescales of ∼2–40 μs for 10 FRBs detected by CHIME/FRB. For the other two FRBs, we did not detect scintillation in the region our analysis is sensitive. We compared the measured scintillation timescales to the NE2001 predictions for the scintillation timescales from the Milky Way. We find a strong correlation to be an indication that in most instances, the observed scintillation of FRBs can be explained by the Milky Way.

Low Correlation Interference OFDM-NLFM Waveform Design for MIMO Radar Based on Alternating Optimization

The OFDM chirp signal is suitable for MIMO radar applications due to its large time-bandwidth product, constant time-domain, and almost constant frequency-domain modulus. Particularly, by introducing the time-frequency structure of the non-linear frequency modulation (NLFM) signal into the design of an OFDM chirp waveform, a new OFDM-NLFM waveform with low peak auto-correlation sidelobe ratio (PASR) and peak cross-correlation ratio (PCCR) is obtained. IN-OFDM is the OFDM-NLFM waveform set currently with the lowest PASR and PCCR. Here we construct the optimization model of the OFDM-NLFM waveform set with the objective function being the maximum of the PASR and PCCR. Further, this paper proposes an OFDM-NLFM waveform set design algorithm inspired by alternating optimization. We implement the proposed algorithm by the alternate execution of two sub-algorithms. First, we keep both the sub-chirp sequence code matrix and sub-chirp rate plus and minus (PM) code matrix unchanged and use the particle swarm optimization (PSO) algorithm to obtain the optimal parameters of the NLFM signal’s time-frequency structure (NLFM parameters). Next, we keep current optimal NLFM parameters unchanged, and optimize the sub-chirp sequence code matrix and sub-chirp rate PM code matrix using the block coordinate descent (BCD) algorithm. The above two sub-algorithms are alternately executed until the objective function converges to the optimal solution. The results show that the PASR and PCCR of the obtained OFDM-NLFM waveform set are about 5 dB lower than that of the IN-OFDM.

Design of Wideband Antenna Array for WiMax Application

The evolution of wireless communication system has led path for innovative antenna design specifically in wideband antenna for WiMax application. In this paper design and simulation of microstrip wideband circular patch antenna array operating between 2GHz to 4Ghz is presented. The circular patch antenna is designed to operate at 3GHz line feed and the ground is itched to achieve required wideband characteristics. The simulation is carried out in EM Flow solver, High Frequency Structure Simulator software. For a single patch antenna, the return loss, lesser than -10dB throughout the bandwidth. Later an antenna array is operating between 2GHz to 4GHz frequency is designed and simulated. The return loss is lesser than -12dBi throughout the band and a peak gain is 14.7dBi. Keywords: Microstrip Patch Antenna (MPA), High Frequency Structure Simulator (HFSS).

Frequency, structure, main causes and outcomes of keratitis caused by wearing contact lenses

Purpose. To study the frequency, structure and outcomes of keratitis caused by wearing contact lenses. Material and methods. A continuous sample of all cases of the incidence of keratitis provoked by an error in wearing contact lenses in adult patients from 2017 to 2019 was carried out. All of them underwent inpatient treatment for this matter in the ophthalmological department of the City Clinical Hospital No. 10 of the Ministry of Health of the Khabarovsk Territory. The provoking factors, etiological structure, the frequency of restoration of visual functions and the outcomes of these keratitis were determined. Results. The total number of cases studied was 51 (52 eyes). Keratitis was provoked by wearing soft contact lenses (SCL) mainly in females (76.5%) aged 20– 30 years. Lenses were selected mainly for moderate myopia (44%). Bacterial etiology of keratitis was detected in 61% of cases, mixed – in 31% of cases, viral – in 8%. The main reason for the development of keratitis is violations in the mode of using SCL (sleep in lenses, prolonged use of SCL with an expired wearing period, violation of the rules for caring for lenses). Conclusion. In the structure of keratitis, provoked by wearing SCL, there were mainly bacterial keratitis (61%). The predominant factors contributing to the formation of keratitis were: sleeping in lenses (51%) and prolonged wearing of lenses exceeding their useful life (24%). The treatment made it possible to completely restore visual functions in 38% of patients. Key words: keratitis, soft contact lenses, myopic refraction.

Investigation of Non-Linear Ship Hydroelasticity by CFD-FEM Coupling Method

With the increase of ship size, the stiffness of the hull structure becomes smaller. This means that the frequency of wave excitation tends to be closer to the natural frequency of the hull vibration, which in turn makes the hydroelastic responses more significant. An accurate assessment of the wave loads and motion responses of hulls is the key to ship design and safety assessment. In this paper, the coupled CFD (Computational Fluid Dynamics)-FEM (Finite Element Method) method is used to investigate the non-linear hydroelasticity effect of a 6750-TEU (Twenty-foot Equivalent Unit) container ship. First, by comparing the heave, pitch, and vertical bending moment at midship section (VBM4) against experimental results reported in the literature, the validity of the numerical method in this paper is illustrated. Secondly, the ship responses under different wave length–ship length ratio, wave frequency-structure natural frequency, wave steepness, and ship speeds are studied. It is found that the wave length–ship length ratio has a more important influence on the hydroelastic response than that from wave frequency-structure natural frequency ratio, and the effect of wave non-linearity will behave differently under different wave length–ship length ratio. The increase of rigid body motion caused by forward speed will not correspondingly increase the non-linearity of the hydroelastic response.

Microstrip-line-fed inverted L-shaped circularly polarized antenna for C-band applications

A circularly polarized stub-matched inverted L-shaped antenna for C-band applications is presented in this communication. Antenna parameters of inverted L-shape on the radiating patch and slits, notch, square strips and stub on the ground plane and the effect of these are analyzed. The proposed optimized antenna (A5: 0.54λ0 × 0.54λ0 × 0.02λ0 mm3) is selected among antennas (A1 – A5) with 5.1 GHz design frequency after simulation through high-frequency structure simulator (HFSS). Circular polarization is obtained by introducing stub/perturbation on the ground plane. By introducing stub, the highest measured (S11 < − 10 dB) impedance bandwidth of 50.9% (3.48 – 5.86 GHz) is observed amongst the reported and compared bandwidths. Peak gain of 5.32 dBi and 3 dB axial ratio bandwidth of 16.2% (4.71 – 5.54 GHz) is reported in the present work. An antenna is useful in the entire downlink frequency (3.7 – 4.2 GHz) of the C band.

Comb Shaped Triple Band Microstrip Antenna for Wireless Communication

A comb shaped microstrip antenna is designed by loading rectangular slots on the patch of the antenna. The antenna resonating at three different frequencies f1 = 5.35 GHz, f2 = 6.19 GHz and f3= 8.15 GHz. The designed antenna is simulated on High Frequency Structure Simulator software [HFSS] and the antenna is fabricated using substrate glass epoxy with dielectric constant 4.4 having dimension of 8x4x0.16 cms. The antenna shows good return loss, bandwidth and VSWR. Experimental results are observed using Vector Analyzer MS2037C/2.