Search Results (100)

Inverse synthetic aperture radar (ISAR) imaging techniques are frequently used in target classification and recognition applications, due to its capability to produce high-resolution images for moving targets. In order to meet the demand of ISAR imaging for electromagnetic calculation with high efficiency and accuracy, a novel accelerated shooting and bouncing ray (SBR) method is presented by combining a Graphics Processing Unit (GPU) and Bounding Volume Hierarchies (BVH) tree structure. To overcome the problem of unfocused images by a Fourier-based ISAR procedure under wide-angle and wide-bandwidth conditions, an efficient parallel back projection (BP) imaging algorithm is developed by utilizing the GPU acceleration technique. The presented GPU-accelerated SBR is validated by comparison with the RL-GO method in commercial software FEKO v2020. For ISAR images, it is clearly indicated that strong scattering centers as well as target profiles can be observed under large observation azimuth angles, $\Delta \phi =90°$, and wide bandwidths, 3 GHz. It is also indicated that ISAR imaging is heavily sensitive to observation angles. In addition, obvious sidelobes can be observed, due to the phase history of the electromagnetic wave being distorted resulting from multipole scattering. Simulation results confirm the feasibility and efficiency of our scheme by combining GPU-accelerated SBR with the BP algorithm for fast ISAR imaging simulation under wide-angle and wide-bandwidth conditions. Full article

In this paper, we propose an imaging method for seafloor features based on multipath arrival structures. The bistatic sonar system employed consists of a vertical transmitting array and a horizontal towed array. The conventional back projection (BP) method, which considers the direct path from the source to the seafloor scatterer and then to the receiver, is used in this system. However, discrepancies between the calculated delay values and the actual propagation delay result in projection deviations and offsets in the seafloor features within sound intensity images. To address this issue, we analyze the multipath structures from the source to the scatterer and then to the receiver based on ray theory. The delay at each grid is calculated using different multipaths, considering the distances from the seafloor grids to the source and the receiver. In the direct zone, the delay is determined using the direct ray and the surface reflection ray, while in the bottom bounce area, the delay is calculated using the bottom–surface reflection ray and the surface–bottom–surface reflection ray. Numerical simulations and experimental results demonstrate that the proposed method rectifies the delay calculation issues inherent in the conventional method. This adjustment enhances the accuracy of the projection, thereby improving the imaging quality of seafloor features. Full article

Cancer cells subvert multiple properties of normal cells, including escaping strict cell cycle regulation, gaining resistance to cell death, and remodeling the tumor microenvironment. The hallmarks of cancer have recently been updated and summarized. Nuclear factor erythroid 2-related factor 1 (NFE2L1, also named NRF1) belongs to the cap’n’collar (CNC) basic-region leucine zipper (bZIP) family. It acts as a transcription factor and is indispensable for maintaining both cellular homoeostasis and organ integrity during development and growth, as well as adaptive responses to pathophysiological stressors. In addition, NFE2L1 mediates the proteasome bounce-back effect in the clinical proteasome inhibitor therapy of neuroblastoma, multiple myeloma, and triple-negative breast cancer, which quickly induces proteasome inhibitor resistance. Recent studies have shown that NFE2L1 mediates cell proliferation and metabolic reprogramming in various cancer cell lines. We combined the framework provided by “hallmarks of cancer” with recent research on NFE2L1 to summarize the role and mechanism of NFE2L1 in cancer. These ongoing efforts aim to contribute to the development of potential novel cancer therapies that target the NFE2L1 pathway and its activity. Full article

This study seeks to investigate the potential effects of the recent pandemic (COVID-19) on capital structure dynamics. The Gulf Cooperation Council (GCC) is a fascinating topic for this study because of its distinct economic characteristics. The analysis draws upon a cross-country dataset covering 208 non-financial listed firms across five GCC countries, with data spanning the years 2010 to 2022. Capital structure is a dependent variable and is measured by total debt to equity, equity multiplier, and short-term debt ratios, while the COVID-19 pandemic, firm size growth, return on assets, tangibility, and growth were applied as independent variables. Using the generalized least squares (GLS) method, findings demonstrated that COVID-19 has a significant and positive influence on debt-to-equity and equity multiplier ratios but a negative one on short-term debt ratio. Thus, non-financial firms increased their debt financing and transferred debt from short-term to long-term funding. In addition, firm-specific factors, such as firm size, tangibility, and macroeconomic factors, such as GDP growth, positively and significantly impact capital financing. Conversely, profitability has a negative relationship with financial leverage. There is a lack of empirical research on how COVID-19 affects the financial structure of non-financial listed companies in GCC nations. Consequently, by filling the previously specified gaps, this study provides proof to support the idea of using debt financing to raise capital for economic recovery. GCC policymakers need to give priority to ensuring that firms have convenient access to inexpensive finance in light of the financial consequences caused by COVID-19. This will guarantee that companies have the resources necessary to bounce back and support economic growth. Full article

The intrusion of micrometer-sensitive contaminant particles into the clearance of sliding valves within hydraulic fluids is one of the root causes of valve sticking and reliability issues in hydraulic systems. To reveal the transient process and characteristics of particle intrusion into the clearance process, this paper proposes a numerical method for fluid–particle one-way coupling and verifies it through experimentation. Furthermore, a numerical simulation of the motion trajectory of spherical iron particles inside the valve chamber was conducted in a two-dimensional flow model. It was discovered that in a steady-state flow field with a certain valve opening, micrometer-sized particles in the valve chamber’s hydraulic fluid mainly move with the valve flow stream, and the number of micron particles invading the slide valve clearance and the probability of invasion is related to the slide valve opening and differential pressure. When the slide valve opening decreases, especially in the small opening state, the probability of particles invading the slide valve clearance will increase dramatically, and the probability of invading the clearance is as high as 27% in a valve opening of 50 μm; the larger the pressure difference between the valve ports, the more the number of particles invading the slide valve clearance increases; the particles in the inlet of the slide valve clearance are more prone to invade the slide valve clearance, and invade in an inclined way, touching the wall and then bouncing back. These findings are of great value for the design of highly reliable hydraulic control valves and the understanding of the mechanism of slide valve stalls and provide an important scientific basis for the optimization and improvement in the reliability of hydraulic systems. Full article

This paper proposes the D2Q5 Lattice Boltzmann method (LBM) method, in two dimensions with five discrete lattice velocities, for simulating linear sound wave propagation in closed rooms. A second-order linear acoustic equation obtained from the LBM method was used as the model equation. Boundary conditions at the domain boundary use the bounce-back scheme. The LBM numerical calculation algorithm in this paper is relatively simpler and easy to implement. Parallelization with the GPU CUDA was implemented to speed up the execution time. The calculation results show that the use of parallel GPU CUDA programming can accelerate the proposed simulation 27.47 times faster than serial CPU programming. The simulation results are validated with analytical solutions for acoustic pulse reflected by the flat and oblique walls, the comparisons show very good concordance, and the D2Q5 LBM has second-order accuracy. In addition, the simulation results in the form of wavefront propagation images in complicated shaped rooms are also compared with experimental photographs, and the comparison also shows excellent concordance. The numerical results of the D2Q5 LBM are promising and also demonstrate the great capability of the D2Q5 LBM for investigating room acoustics in various complexities. Full article

Real-time visual object tracking (VOT) may suffer from performance degradation and even divergence owing to inaccurate noise statistics typically engendered by non-stationary video sequences or alterations in the tracked object. This paper presents a novel adaptive Kalman filter (AKF) algorithm, termed AKF-ALS, based on the autocovariance least square estimation (ALS) methodology to improve the accuracy and robustness of VOT. The AKF-ALS algorithm involves object detection via an adaptive thresholding-based background subtraction technique and object tracking through real-time state estimation via the Kalman filter (KF) and noise covariance estimation using the ALS method. The proposed algorithm offers a robust and efficient solution to adapting the system model mismatches or invalid offline calibration, significantly improving the state estimation accuracy in VOT. The computation complexity of the AKF-ALS algorithm is derived and a numerical analysis is conducted to show its real-time efficiency. Experimental validations on tracking the centroid of a moving ball subjected to projectile motion, free-fall bouncing motion, and back-and-forth linear motion, reveal that the AKF-ALS algorithm outperforms a standard KF with fixed noise statistics. Full article

This research paper delves into the multifaceted relationships between psychological resilience, organizational trust, life satisfaction, and organizational resilience within the context of tourism firms in Egypt. Against the backdrop of the COVID-19 pandemic and its profound effects on the tourism industry, the study aims to unravel the intricate interplay of individual and organizational factors that contribute to the adaptive capacity and well-being of employees. The research employs a quantitative methodology, engaging full-time sales and marketing employees from five-star hotels and class A travel agents (660) as key participants, employing SmartPLS-SEM vs4 to analyze the collected data. Through a nuanced examination of their experiences post-pandemic, the study investigates how psychological resilience, defined as the ability to bounce back from adversity, influences both life satisfaction and organizational resilience. Additionally, the impact of organizational trust, characterized by the confidence and faith employees place in their organization, on life satisfaction and organizational resilience is explored. Preliminary findings suggest a positive association between psychological resilience and both life satisfaction and organizational resilience. Employees exhibiting higher levels of psychological resilience tend to not only experience greater life satisfaction but also contribute significantly to their organization’s resilience. Furthermore, organizational trust emerges as a critical factor, positively influencing life satisfaction and organizational resilience. The study contributes valuable insights to the evolving landscape of tourism management and lays the foundation for future research endeavors in this domain. Full article

In this work, a lattice Boltzmann method (LBM) for studying microchannel gas flow is developed in the multi-flow regime. In the LBM, by comparing previous studies’ results on effective viscosity in multi-flow regimes, the values of the rarefaction factor applicable to multi-flow regions were determined, and the relationship between relaxation time and Kn number with the rarefaction factor is given. The Kn number is introduced into the second-order slip boundary condition together with the combined bounce-back/specular-reflection (CBBSR) scheme to capture the gas flow in the multi-flow regime. Sensitivity analysis of the dimensionless flow rate to adjustable parameters using the Taguchi method was carried out, and the values of adjustable parameters were determined based on the results of the sensitivity analysis. The results show that the dimensionless flow rate is more sensitive to j than h. Numerical simulations of Poiseuille flow and pulsating flow in a microchannel with second-order slip boundary conditions are carried out to validate the method. The results show that the velocity profile and dimensionless flow rate simulated by the present numerical simulation method in this work are found in the multi-flow regime, and the phenomenon of annular velocity profile in the microchannel is reflected in the phases. Full article

The rational structural design of polycrystalline diamond compact (PDC) cutters effectively enhances the performance of drill bits in rock fragmentation and extends their service life. Inspired by bionics, a bionic PDC cutter was designed, taking the mole claw toe, shark tooth, and microscopic biomaterial structures as the bionic prototypes. To verify its rock-breaking effectiveness, the finite element method was employed to compare the rock-breaking processes of the bionic cutter, triangular prism cutter, and axe cutter. The study also investigated the influence of different back rake angles, cutting depths, arc radii, and hydrostatic pressures on rock breaking using the bionic cutter. Prior to this, the accuracy of the finite element model was validated through laboratory tests. Subsequently, a drill bit incorporating all three types of cutters was constructed, and simulations of rock breaking were conducted on a full-sized drill bit. The results demonstrate that the bionic cutter exhibits superior load concentration on the rock compared to the triangular prism cutter and the axe cutter. Additionally, its arc structure facilitates the “shoveling” of the rock, making it more susceptible to breakage under tensile stress. As a result, the efficiency of the bionic cutter surpasses that of the triangular prism and axe cutters. Similarly, it exhibits minimal fluctuations and values in cutting force. As the back rake angle and cutting depth increase, the MSE and cutting force of all three cutters also increase. However, the bionic cutter consistently maintains the lowest MSE and cutting force, confirming the superiority of its bionic structural design. The MSE and cutting force of the bionic cutter fluctuate with the increase of the arc radius, and the optimal arc radius falls within the simulation range, between 21 mm and 23 mm. Compared to the other two types of cutters, bionic cutters possess a unique structure that allows for better release of internal stress within the rock, thereby ensuring higher efficiency in rock-breaking, particularly in deep geological formations. The rock breaking simulation results of full-sized drill bits show that the use of a bionic cutter can improve the drill bit’s ability to penetrate the formation, reduce the possibility of drill bit bounce during the rock breaking process, prevent the occurrence of stick-slip, improve the drilling stability, effectively improve the efficiency and service life of the drill bit during the rock breaking process, and reduce the drilling cost. It is concluded that the research results of bionic PDC cutters are helpful to the development of high-performance drill bits and the reduction of drilling costs. Full article

An unmanned aerial vehicle (UAV) swarm is a fast-moving system where self-adaption is necessary when conducting a mission. The major causative factors of mission failures are inevitable disruptive events and uncertain threats. Given the unexpected disturbances of events and threats, it is important to study how a UAV swarm responds and enable the swarm to enhance resilience and alleviate negative influences. Cooperative adaptation must be established between the swarm’s structure and dynamics, such as communication links and UAV states. Thus, based on previous structural adaptation and dynamic adaptation models, we provide a co-adaptation model for UAV swarms that combines a swarm’s structural characteristics with its dynamic characteristics. The improved model can deal with malicious events and contribute to a rebound in the swarm’s performance. Based on the proposed co-adaptation model, an improved resilience metric revealing the discrepancy between the minimum performance and the standard performance is proposed. The results from our simulation experiments show that the surveillance performance of a UAV swarm bounces back to its initial state after disruptions happen in co-adaptation cases. This metric demonstrates that our model can contribute towards the swarm’s overall systemic resiliency by withstanding and resisting unpredictable threats and disruptions. The model and metric proposed in this article can help identify best practices in improving swarm resilience. Full article

Existential threats from climate change, weather-related disasters, and other crises have drawn increasing attention to urban resilience. Prior work has focused on explicating resilience and proposing various definitions of it. But the emphasis on describing resilience might overlook what urban means in discussions of urban resilience. This paper investigates how urban resilience scholarship conceptualizes and defines the term urban. I conduct a literature review and content analysis of recently published urban resilience articles. The results reveal how urban is prominently featured, but its conceptual use is not identified, and the term is left undefined. The findings suggest serious concerns about the applicability and generalizability of urban resilience to different contexts. The paper contributes to the literature by showing how conceptualizing urban alternately as a shared subject of study, influential condition, or measurement category has far-reaching implications for urban resilience planning, implementation, and assessment. Drawing upon the idea of simulated annealing, the paper suggests that taking a few conceptual steps backward may help our understanding of urban resilience—and cities to bounce back better. Full article

Background and Objectives: The fatigue, stress, and burnout of nurses lead to them frequently making mistakes, which have a negative impact not only on the safety of the patients but also on their psychology. The ability to bounce back from mistakes is crucial for nurses. Nursing staff members’ physical and mental health, particularly their depression, is far from ideal, and this ill health is directly correlated with the frequency of self-reported medical errors. The nurses’ mental and physical health are also positively correlated with their perception of wellness support at work. This cross-sectional study aimed to investigate the status of nurses’ mental and physical health regarding clinical errors and the impact of resilience on coping with these situations. Materials and Methods: A total of 364 healthcare professionals participated in this research; 87.5% of them were females and 12.5% of them were males. Most of the participants were 22–35 years old. The median number of years of employment was nine. Clinical nurses anonymously and voluntarily completed a special structured questionnaire that included questions from different validated tools in order to assess their state of physical and mental wellbeing after events of stress and errors made during their practice. Results: In total, 49.4% of the nurses had made an error on their own, and 73.2% had witnessed an error that someone else had made. At the time of the error, 29.9% of the participants were in charge of more than 20 patients, while 28.9% were responsible for a maximum of three patients. Participants who were 36–45 years old had more resilience (p = 0.049) and experienced fewer negative emotions than participants who were 22–35 years old. The participants who mentioned more positive feelings according to their mental state had greater resilience (p > 0.001). Conclusions: Errors were likely to happen during clinical practice due to nurses’ negative experiences. The level of resilience among the nursing population was found to play a very important role not only in making mistakes but also in coping with errors during their daily routine. Wellness and prevention must be given top priority in all healthcare systems across the country in order to promote nurses’ optimal health and wellbeing, raise the standard of care, and reduce the likelihood of expensive, avoidable medical errors. Healthcare administrations should promote prevention programs for stress occurrence in order to support nurses’ wellbeing maintenance. Full article

While the definition of resilience is disputed or even fuzzy, due in no small part to the diversity of its applications, the concept generally involves the ability to withstand and bounce back from shocks; vulnerability as a related concept involves the tendency to suffer from shocks, given existing characteristics that may prevent resilient responses. Vulnerabilities put individuals, groups, and societies at greater risk and disadvantage, suggesting a need not only for disaster response and recovery, but mitigation and preparedness. Resilience and vulnerability research has recently focused on the role of government, the COVID-19 pandemic, and flood hazards; topics of interest have also included resilience of rural and urban areas, development and sustainability, and displacement and migration. Full article

A hallmark of aging and neurodegenerative diseases is a disruption of proteome homeostasis (“proteostasis”) that is caused to a considerable extent by a decrease in the efficiency of protein degradation systems. The ubiquitin proteasome system (UPS) is the major cellular pathway involved in the clearance of small, short-lived proteins, including amyloidogenic proteins that form aggregates in neurodegenerative diseases. Age-dependent decreases in proteasome subunit expression coupled with the inhibition of proteasome function by aggregated UPS substrates result in a feedforward loop that accelerates disease progression. Nuclear factor erythroid 2- like 1 (NFE2L1) is a transcription factor primarily responsible for the proteasome inhibitor-induced “bounce-back effect” regulating the expression of proteasome subunits. NFE2L1 is localized to the endoplasmic reticulum (ER), where it is rapidly degraded under basal conditions by the ER-associated degradation (ERAD) pathway. Under conditions leading to proteasome impairment, NFE2L1 is cleaved and transported to the nucleus, where it binds to antioxidant response elements (AREs) in the promoter region of proteasome subunit genes, thereby stimulating their transcription. In this review, we summarize the role of UPS impairment in aging and neurodegenerative disease etiology and consider the potential benefit of enhancing NFE2L1 function as a strategy to upregulate proteasome function and alleviate pathology in neurodegenerative diseases. Full article