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

Impact of Ultra-Low Interfacial Tension on Enhanced Oil Recovery of Ultra-Low Permeability Reservoir

Ultra-low permeability reservoirs have the characteristics of complex pore throat structure, generally higher injection pressure and lower oil recovery. By means of casting thin sections, pore structure of selected ultra-low permeability core was surveyed. The core was classified into low porosity, low permeability and without natural fractures. Vast majority of throats of the core varied in width from 2.5 μm to 15 μm. Core displacement experiments showed that surfactant flooding could have certain effect of reducing injection pressure and enhancing oil recovery. When interfacial tension was 5.93×10-2 mN/m, decompression rate reached 7.65%, and recovery was improved by 4.09%. And when interfacial tension was 4.9×10-5 mN/m, decompression rate reached 25%, and recovery was improved by 11.6%. The lower interfacial tension is, the better the effect of reducing injection pressure is, and the higher the extent of enhancing oil recovery is. In general, surfactants have a great application prospect on the oil field development of ultra-low permeability reservoir, and the interfacial tension should be reduced as far as possible.Key words: Low permeability; Surfactant; Interfacial tension; Emulsion; Enhancing oil recover

The Potential Geographical Distribution of Bactrocera cucurbitae (Diptera: Tephritidae) in China Based on Eclosion Rate Model and ArcGIS

Abstract. The melon fruit fly, Bactrocera cucurbitae Coquillett (Diptera: Tephritidae), is one of the important insect pests of fruits and vegetables. In order to monitor and control it effectively, it is necessary to know the potential geographical distribution of this pest. The ER (Eclosion rate) model was constructed from empirical biological data, and analyzed with ArcGIS. Based on the soil temperature and moisture data of Chinese meteorological stations, the potential geographical distribution of B. cucurbitae from January to December in China was predicted. Six categories were used to describe different levels of suitability for B. cucurbitae in China. The potential geographical distribution and suitable levels for every month in China were obtained and showed that almost all locations were suitable from May to September. Further analysis showed that monitoring measures should be taken in Guangdong, Guangxi, Yunnan, and Hainan provinces throughout the year

How does workplace support promote postdoctoral career growth? A conservation of resources perspective

BackgroundPostdoctoral researchers are critical to scholarly advancements, and promoting postdoctoral career growth is an endogenous path to help postdocs break through the “encircled city of scientific research”. However, further research is needed to fully explore the mechanisms that connect workplace support to postdoctoral career growth.MethodsDrawing from the Conservation of Resources theory, this study proposes a chain mediation model that demonstrates how workplace support enhances career growth by connecting psychological capital with work-life balance. To understand the motivation and career growth of postdocs in China, we conducted two questionnaires in 2021 and 2023 with the support of relevant stations.ResultsAnalyzing 367 questionnaires from Chinese postdocs, our research indicates that workplace support has a positive impact on career growth. Additionally, both psychological capital and work-life balance are key factors that contribute to career growth, serving as separate mediators and as part of a chain of mediators.DiscussionThis study validates the appropriateness of the Conservation of Resources theory in the study of the influence mechanism of postdoctoral career growth and proposes targeted strategies for academic institutions to improve support systems, promoting more effective career development pathways

Государственная политика по совершенствованию рыночных механизмов регулирования интеллектуальной миграции как основа возрождения интеллектуального потенциала России (на примере томских вузов)

На основе глубокого анализа текущего состояния научно-образовательного комплекса и государственной политики, регулирующей международной интеллектуальной миграции, выявлены факторы, влияющих на эффективность реализации государственной политики в части регулирования международной интеллектуальной миграции в РФ.Based on a deep analysis of the current state of the scientific and educational complex and state policy regulating international intellectual migration, factors influencing the effectiveness of the implementation of state policy regarding the regulation of international intellectual migration in the Russian Federation were revealed

A Hybrid Approach to Explore the Risk Dependency Structure among Agribusiness Firms

Although the risk management of agricultural firms is important, studies on the extreme risk dependence among agribusiness firms are minimal due to the diversity and complexity of the risks faced by agricultural firms. In this study, we developed a hybrid approach to analyse and uncover the potential risk dependence among agricultural firms. We examined thirty-two agricultural companies to study their dependence structure for risk losses. Three primary findings emerged. First, risk dependence is strong with an average value of 0.96. Second, the dependence structure is hierarchical and includes two network communities. Third, some key agricultural firms were identified in the dependence structure. These key firms are critical for the transmission of negative impacts across agricultural firms. Correspondingly, we suggest measures and strategies (such as improving the level of technological innovation and joint risk resistance capability) to reduce the impact of risk dependence