Unmanned aerial vehicles (UAVs) have attracted great interest in rapid deployment for both civil and military applications. UAV communication has its own distinctive channel characteristics compared ...to the widely used cellular or satellite systems. Accurate channel characterization is crucial for the performance optimization and design of efficient UAV communication. However, several challenges exist in UAV channel modeling. For example, the propagation characteristics of UAV channels are under explored for spatial and temporal variations in non-stationary channels. Additionally, airframe shadowing has not yet been investigated for small size rotary UAVs. This paper provides an extensive survey of the measurement methods proposed for UAV channel modeling that use low altitude platforms and discusses various channel characterization efforts. We also review from a contemporary perspective of UAV channel modeling approaches, and outline future research challenges in this domain.
Math anxiety (MA) has been suggested to decrease the math performance of students. However, it remains unclear what factors moderate this relationship. The aim of this research was to explore the ...link between MA and math performance. Studies that explored the math anxiety-performance link, conducted from 2000 to 2019 (84 samples,
= 8680), were identified and statistically integrated with a meta-analysis method. The results indicated a robust negative math anxiety-performance link. Furthermore, regarding the analysis of moderator variables, this negative link was stronger in the studies that involved Asian students, but this link was the weakest in the studies that involved European students. Moreover, this negative link was stronger in the studies within a senior high school group, whereas it was the weakest in the studies within an elementary group. Finally, this negative link was strongest among studies that used a custom test and studies that assessed problem-solving skills. Potential explanations and implications for research and practice are discussed.
Environment-friendly, function tunable, and low-cost adsorbents/amendments from agricultural residue-derived biochar show enormous potential for mitigating the environment problems. A series of ...nano-sized goethite modified biochar (GMB) material were synthesized by co-precipitating with crop residue-derived biochar and could be used for amelioration of cation, anion, antibiotics, and non-point source pollutant in both soil and water. The GMB materials were characterized by SEM-EDS, BET, FTIR, XRD, VSM, and XPS analysis. Their adsorption performance for cationic Cd(II), anionic As(III), antibiotics roxarsone (ROX), and non-point source pollutant phosphorus in water was evaluated by adsorption kinetics and equilibrium experiments. Based on Langmuir model, the maximum adsorption capacities of Cd(II), As(III), ROX, and phosphorus were 31.9, 65.3, 66.5, and 42.7 mg/g, respectively, which were enhanced by 135%, 6279%, 961%, and 2437% compared to pristine biochar. The adsorption behavior of GMB can be explained by non-specific adsorption (electrostatic interaction and physical adsorption), specific adsorption (hydroxyl complex, π-π interaction, surface complexation, ion exchange, etc.), and chemisorption induced by goethite nanoparticles on the GMB. Moreover, GMB (1 wt%) also performed well for immobilization of these four contaminants in soil. After GMB treatment, the concentrations of available Cd, As, ROX, and phosphorus in soil decreased by 74.1%, 58.7%, 70.8%, and 29.1%, respectively. This study proposed that the scalable GMB can be considered as a sustainable multifunctional material for soil and water decontamination.
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•Nano-sized goethite modified biochar (GMB) was generated by co-precipitation.•GMB showed good adsorption performance for Cd(II), As(III), ROX, and phosphate.•FTIR and XPS confirmed the complexation and ion exchange for tested contaminants.•GMB effectively immobilized Cd(II), As(III), ROX, and phosphorus in contaminated soil.
Validation is the process of conducting a validity study on a test, gathering evidence to support inferences made based on test scores. Using many-facet Rasch analysis this paper validates the result ...of a consecutive interpreting test from four aspects: rating scale, raters, examinees and interpreting tasks. The study also identifies factors that affect the test results through bias analysis. The results of this analysis show that: (1) this analytical rating scale and task design can effectively reflect the examinees' interpreting competence, thus making it suitable for validating interpreting assessments; (2) one of the sub-scales: interpreting skills and manners, has a slightly negative effect on the overall validity of the assessment, making further revision on this sub-scale desirable.
Unmanned aerial vehicles (UAVs) can help small-cell base stations (SBSs) offload traffic via wireless backhaul to improve coverage and increase rate. However, the capacity of backhaul is limited. In ...this paper, UAV assisted secure transmission for scalable videos in hyper-dense networks via caching is studied. In the proposed scheme, UAVs can act as SBSs to provide videos to mobile users in some small cells. To reduce the pressure of wireless backhaul, UAVs and SBSs are both equipped with caches to store videos at off-peak time. To facilitate UAVs, a single antenna is equipped at each UAV and thus, only the precoding matrices of SBSs should be cooperatively designed to manage interference by exploiting the principle of interference alignment. On the other hand, the SBSs replaced by UAVs will be idle. Thus, in order to guarantee secure transmission, the idle SBSs can be further exploited to generate jamming signal to disrupt eavesdropping. The jamming signal is zero-forced at the legitimate users through the precoding of the idle SBSs, without affecting the legitimate transmission. The feasibility conditions of the proposed scheme are derived, and the secrecy performance is analyzed. Finally, simulation results are presented to verify the effectiveness of the proposed scheme.
Sepsis-associated cerebral dysfunction is complex pathophysiology, generated from primary infections that are developed elsewhere in the body. The neonates, elderly population and chronically ill and ...long-term hospitalized patients are predominantly vulnerable to sepsis and related cerebral damage. Generally, electrophysiological recordings, severity and sedation scales, computerized imaging and spectroscopy techniques are used for its detection and diagnosis. About the underlying mechanisms, enhanced blood-brain barrier permeability and metalloprotease activity, tight junction protein loss and endothelial cell degeneration promote the influx of inflammatory and toxic mediators into the brain, triggering cerebrovascular damage. An altered neutrophil count and phenotype further dysregulate the normal neuroimmune responses and neuroendocrine stability via modulated activation of protein kinase C-delta, nuclear factor kappa-B and sphingolipid signaling. Glial activation, together with pro-inflammatory cytokines and chemokines and the Toll-like receptor, destabilize the immune system. Moreover, superoxides and hydroperoxides generate oxidative stress and perturb mitochondrial dynamics and ATP synthesis, propagating neuronal injury cycle. Activated mitochondrial apoptotic pathway, characterized by increased caspase-3 and caspase-9 cleavage and Bax/Bcl2 ratio in the hippocampal and cortical neurons, stimulate neurocognitive impairments. Additionally, altered LC3-II/I and P62/SQSTM1, p-mTOR, p-AMPK1 and p-ULK1 levels and dysregulated autophagosome-lysosome fusion decrease neuronal and glial energy homeostasis. The therapies and procedures for attenuating sepsis-induced brain damage include early resuscitation, cerebral blood flow autoregulation, implantable electric vagus nerve stimulation, antioxidants, statins, glucocorticoids, neuroimmune axis modulators and PKCδ inhibitors. The current review enumerates the pathophysiology of sepsis-induced brain damage, its diagnosis, the role of critical inducers and mediators and, ultimately, therapeutic measures attenuating cerebrovascular degeneration.
Power electronic traction transformer (PETT) is a new topology for a traction drive system, which can realize the high voltage and power conversion through multilevel converters and ...high-/medium-frequency transformer link. Reliability becomes a key issue for PETT adopting the module-cascaded structure. In this paper, an improved fault-tolerant method based on reverse-charging control of dual active bridge is proposed, which is suitable for PETT and other two-stage structure converters. The control strategy and operating process of an improved fault-tolerant method are introduced. Comparisons among improved and traditional fault-tolerant methods are also presented. Simulation and experimental results are provided to show the correctness and effectiveness of the improved fault-tolerant method.
Problem
Endometriosis patients undergoing in vitro fertilization‐embryo transfer (IVF‐ET) treatment suffer from poor oocyte quality, a reduced likelihood of the fertilization rate, and low embryo ...quality. The dysregulation of immune cells and cytokine profiles in the follicular fluid (FF) may play an important role in the competence of the oocyte and the development of the embryo, but the mechanism remains largely unknown.
Method of Study
A total of 40 proved advanced staged endometriosis patients were enrolled in this study. The pregnancy results were followed until all the embryos collected by the first oocyte retrieval cycle were used up. The immune cells subtypes in FF and serum collected on the day of oocyte retrieval were detected by flow cytometry and 27 cytokines were determined using the Bio‐Plex Pro Human Cytokine 27‐Plex Immunoassay. The specific effect of cytokine on the gene expression of human granulosa cells was determined by RT‐qPCR.
Results
The fertilization rate and the cumulative live birth rate were significantly lower in the endometriosis group. The ratio of CD4+/CD8+T cells in FF was significantly lower, while the level of IP‐10, RANTES and G‐CSF were statistically higher in the endometriosis group. The level of IP‐10 correlated with the IVF outcome. Moreover, treated by IP‐10, the mRNA level of FSHR and CYP19A1 the human granulosa cells were downregulated in vitro.
Conclusion
These results suggest that alterations of the lymphocyte subsets and cytokines in women with advanced endometriosis may have an impact on the oocyte development and resulting in poorer IVF outcomes.
The quality control of plastic products is an essential aspect of the plastic injection molding (PIM) process. However, the warpage and shrinkage deformations continue to exist because the PIM ...process is easily interfered with by several related or independent process parameters. Thus, great efforts have been devoted to optimizing process parameters to minimize the warpage and shrinkage deformations of products during the last decades. In this review, we begin by introducing the manufacturing process in PIM and the cause of warpage and shrinkage deformations, followed by the mechanism about how process parameters, like mold temperature, melt temperature, injection rate, injection pressure, holding pressure, holding and cooling duration, affect those defects. Then, we summarize the recent progress of the design of experiments and four advanced methods (artificial neural networks, genetic algorithm, response surface methodology, and Kriging model) on optimizing process parameters to minimize the warpage and shrinkage deformations. In the end, future perspectives of quality control in injection molding machines are discussed.
This paper constructs the 6E evaluation index system, a comprehensive index including the dimensions of economy, effectiveness, efficiency, equity, earnings and equality, to measure the sustainable ...higher education development of the 31 provincial regions of China by utilizing the information entropy weight-TOPSIS method. This paper then makes a spatial and temporal analysis of the coupling coordination relationship among the dimensions of sustainable higher education development by using the coupling coordination model. In addition, this paper proposes specific and applicable countermeasures for sustainable higher education development. The results show that the comprehensive degrees of sustainable higher education development in most regions are not high, and the coastal regions and the Central-south China regions have higher grades; in addition, for most regions, the coupling coordination degrees mainly remain stable, with mild growth in the respective classifications, and the gap between the west and other regions is declining. The improved method is applicable to measure the sustainable development of higher education and to propose detailed and appropriate suggestions for further development.
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