Search

The extensive deployment of wind farms has significantly impacted the detection capabilities of space–air bistatic radar (SABR) systems. Although space–time adaptive processing techniques are available, their performance is significantly degraded, and even unable to suppress clutter. This paper explores the geometric configuration of the SABR system and the selection of detection areas, establishing a space–time clutter model that addresses the effects of wind turbine clutter (WTC). Expressions for spatial and Doppler frequencies have been derived to deeply analyze the characteristics of clutter spreading. Building on this, the paper extends two-dimensional space–time data to three-dimensional azimuth–elevation–Doppler data. It proposes a three-dimensional space–time multi-beam (STMB) strategy incorporating the Ordering Points to Identify the Clustering Structure (OPTICS) clustering algorithm to suppress WTC effectively. This algorithm selects WTC samples and applies OPTICS clustering to the clutter-suppressed data to achieve this effect. Simulation experiments further verify the effectiveness of the algorithm. [ABSTRACT FROM AUTHOR]

Echolocating bats are known to vary their waveforms at the phases of searching, approaching, and capturing the prey. It is meaningful to estimate the parameters of the calls for bat species identification and the technological improvements of the synthetic systems, such as radar and sonar. The type of bat calls is species-related, and many calls can be modeled as hyperbolic frequency- modulated (HFM) signals. To obtain the parameters of the HFM-modeled bat calls, a reversible integral transform, i.e., hyperbolic scale transform (HST), is proposed to transform a call into two-dimensional peaks in the "delay-scale" domain, based on which harmonic separation and parameter estimation are realized. Compared with the methods based on time-frequency analysis, the HST-based method does not need to extract the instantaneous frequency of the bat calls, only searching for peaks. The verification results show that the HST is suitable for analyzing the HFM-modeled bat calls containing multiple harmonics with a large energy difference, and the estimated parameters imply that the use of the waveforms from the searching phase to the capturing phase is beneficial to reduce the ranging bias, and the trends in parameters may be useful for bat species identification. [ABSTRACT FROM AUTHOR]

Sea clutter is a kind of ubiquitous interference in sea-detecting radars, which will definitely influence target detection. An accurate sea clutter prediction method is supposed to be beneficial while existing prediction methods are based on the one-step-ahead prediction. In this paper, a sea clutter prediction network (SCPNet) is proposed to achieve the k-step-ahead prediction based on the characteristics of sea clutter. The SCPNet takes a sequence-to-sequence (Seq2Seq) structure as the backbone, and a simple self-attention module is employed to enhance the ability of adaptive feature selections. The SCPNet takes the normalized amplitudes of sea clutter as inputs and is capable of predicting an output sequence with a length of k; the phase space reconstruction theory is also used to find the optimized input length of the sea clutter sequence. Results with the sea-detecting radar data-sharing program (SDRDSP) database show the mean square error of the proposed method is 1.48 × 10−5 and 8.76 × 10−3 in the one-step-ahead prediction and the eight-step-ahead prediction, respectively. Compared with four existing methods, the proposed method achieves the best prediction performance. [ABSTRACT FROM AUTHOR]

For adaptive multichannel radar detection in the framework of multiple alternative hypotheses, where either the target or jamming could be present, a kind of two‐stage detector and classifier is proposed. Precisely, in the first stage, a decision is made on whether a target or a jamming exists. In the second stage, the decision is determined whether it is a target or a jamming. The detector is chosen as subspace‐based adaptive matched filter (SAMF) or adaptive energy detector (AED), while the classifier is selected as the subspace‐based adaptive beamformer orthogonal rejection test (SABORT), whitened SABORT (W‐SABORT), or orthogonal subspace‐based generalised likelihood ratio test (OSGLRT). Among these detectors and classifiers, the OSGLRT is proposed specially for classification in the scheme. Numerical experiments indicate that the proposed methods can achieve better detection and classification performance. [ABSTRACT FROM AUTHOR]

Explosion often has a chain reaction in the accident field. The aerosol is injected into the high-temperature and high-pressure area produced in the first explosion and a superimposed explosion may be induced. To study this chain process, hazards in the secondary explosion of propylene oxide aerosol was numerically simulated. The superimposed explosion overpressure and temperature of propylene oxide aerosol produced in the secondary explosion are much higher than those in the first explosion. The overpressure of 0.5MPa and the temperature of 2200 K in the first explosion are increased to higher than 2.6 MPa and 3300 K in the secondary explosion, respectively. The secondary explosions of fuel aerosol are even more terrifying in the accident field. More attention should be paid to the superimposed explosion effect. The aerosols with the smaller droplet sizes react more quickly after they are injected into the high-temperature area produced in the first explosion. The superimposed pressure of aerosol with the smaller droplet sizes is higher in near field, but its effect range is shorter than that with the larger droplet sizes. The effect of droplet sizes on superimposed explosion overpressures for the PO aerosol with droplet sizes smaller than 0.2 mm is slight. [ABSTRACT FROM AUTHOR]

The present study aimed to retrospectively assess the effects of human epidermal growth factor receptor 2 (HER2) expression on the diagnosis of patients with hormone receptor (HR)+/HER2− late-stage breast cancer undergoing advanced first-line endocrine-based treatment. A total of 72 late-stage breast tumor cases from June 2017 to June 2019 were selected from the Department of Surgical Oncology, Shaanxi Provincial People's Hospital (Xi'an, China) and included in the present study. The expression of estrogen receptor, progesterone receptor and HER2 was detected by immunohistochemistry. The subjects were divided into two groups: the HER2-negative (0) cohort (n=31) and the HER2 low expression cohort (n=41). The age, BMI, Karnofsky Performance Status (KPS) score, tumor size, lymph node metastasis, pathological type, Ki-67 expression and menopausal status of the patients were obtained through the electronic medical record system of Shaanxi Provincial People's Hospital. Progression-free survival (PFS) and overall survival (OS) were evaluated for all patients. The median PFS and OS of the HER2(0) cohort were longer than those of the HER2 low expression cohort (all P<0.05). It was shown that age (hazard ratio, 6.000 and 5.465), KPS score (hazard ratio, 4.000 and 3.865), lymph node metastasis (hazard ratio, 3.143; 2.983) and HER2 status (hazard ratio, 3.167 and 2.996) were independent influencing factors of the prognosis of patients with HR+/HER2− advanced breast cancer (ABC) (all P<0.05). Three models (model 1, no parameters adjusted; model 2, BMI, tumor size, pathological type, Ki-67 and menopausal status adjusted; and model 3, age, KPS functional status score and lymph node metastasis adjusted based on model 2) were established within the HER2(0) cohort as the reference for statistical analysis using the multivariate Cox's regression test. In models 2 and 3, the risk of poor prognosis of ABC within the HER2 low expression cohort was significantly higher compared with that in the HER2(0) cohort (hazard ratio, 3.558 and 4.477; 95% CI, 1.349-9.996 and 1.933-11.586; P=0.003 and P<0.001). The HER2 expression status of patients with HR+/HER2− ABC receiving advanced first-line endocrine therapy may affect PFS and OS. [ABSTRACT FROM AUTHOR]