Search Results (883)

Swifts, a distinctive avian cohort, have garnered widespread attention owing to their exceptional flight agility. While their aerial prowess is well documented, the challenge swifts encounter while imbibing water introduces an intriguing complexity. The act of water uptake potentially disrupts their flight equilibrium, yet the mechanisms enabling these birds to maintain stability during this process remain enigmatic. In this study, we employed high-speed videography to observe swifts’ water-drinking behavior. Notably, we observed that the swift adopts a dynamic V-shaped wing configuration during water immersion with the ability to modulate the V-shaped angle, thereby potentially fine-tuning their balance. To delve deeper, we utilized a three-dimensional laser scanner to meticulously construct a virtual 3D model of swifts, followed by computational fluid dynamics simulations to quantitatively assess the mechanical conditions during foraging. Our model indicates that the adoption of V-shaped wings, with a variable wing angle ranging from 30 to 60 degrees, serves to minimize residual torque, effectively mitigating potential flight instability. These findings not only enhance our comprehension of swifts’ flight adaptability but also hold promise for inspiring innovative, highly maneuverable next-generation unmanned aerial vehicles. This research thus transcends avian biology, offering valuable insights for engineering and aeronautics. Full article

The volume of fluid (VOF) method is a popular technique for the direct numerical simulations of flows involving immiscible fluids. A discrete volume fraction field evolving in time represents the interface, in particular, to compute its geometric properties. The height function method (HF) is based on the volume fraction field, and its estimate of the interface curvature converges with second-order accuracy with grid refinement. Data-driven methods have been recently proposed as an alternative to computing the curvature, with particular consideration for a well-balanced input data set generation and symmetry preservation. In the present work, a two-layer feed-forward neural network is trained on an input data set generated from the height function data instead of the volume fraction field. The symmetries for rotations and reflections and the anti-symmetry for phase swapping have been considered to reduce the number of input parameters. The neural network can efficiently predict the local interface curvature by establishing a correlation between curvature and height function values. We compare the trained neural network to the standard height function method to assess its performance and robustness. However, it is worth noting that while the height function method scales perfectly with a quadratic slope, the machine learning prediction does not. Full article

Probiotics restore gut microbial balance, thereby providing health-promoting effects to the host. They have long been suggested for managing intestinal disorders caused by pathogens and for improving gut health. This study evaluated the probiotic properties and anti-pathogenic effects of specific probiotic strains against the intestinal pathogens Staphylococcus aureus and Escherichia coli. The tested strains—Lactiplantibacillus plantarum LC27, Limosilactobacillus reuteri NK33, Lacticaseibacillus rhamnosus NK210, Bifidobacterium longum NK46, and Bifidobacterium bifidum NK175—were able to survive harsh conditions simulating gastric and intestinal fluids. These strains exhibited good auto-aggregation abilities (41.8–92.3%) and ideal hydrophobicity (30.9–85.6% and 38.3–96.1% for xylene and chloroform, respectively), along with the ability to co-aggregate with S. aureus (40.6–68.2%) and E. coli (38.6–75.2%), indicating significant adhesion levels to Caco-2 cells. Furthermore, these strains’ cell-free supernatants (CFSs) demonstrated antimicrobial and antibiofilm activity against S. aureus and E. coli. Additionally, these strains inhibited gas production by E. coli through fermentative activity. These findings suggest that the strains tested in this study have potential as novel probiotics to enhance gut health. Full article

Gusts have a significant impact on aircraft and need to be analyzed through flight simulations. The solution for time-domain gust aerodynamic forces stands as a pivotal stage in this process. With the increasing demand for flight simulations within gusty environments, traditional methods related to gust aerodynamics cannot fail to balance computational accuracy and efficiency. A method that can be used to quickly and accurately calculate the time-domain gust aerodynamic force is needed. This study proposes the fitting strip method, a gust aerodynamic force solution method that is suitable for real-time flight simulations. It only requires the current and previous gust information to calculate the aerodynamic force and is suitable for different configurations of aircraft and different kinds of gusts. Firstly, the fitting strip method requires the division of fitting strips and the calculation of the aerodynamic force under calibration conditions. In this study, the double-lattice method and computational fluid dynamics are used to calculate the aerodynamic force of the strips. Then, the amplitude coefficients and time-delay coefficients are obtained through a fitting calculation. Finally, the coefficients and gust information are put into the formula to calculate the gust aerodynamic force. An example of a swept wing is used for validation, demonstrating congruence between the computational results and experimental data across subsonic and transonic speeds, which proves the accuracy of the fitting strip method in both discrete gusts and continuous gusts. Compared with other methods, the fitting strip method uses the shortest time. Furthermore, the results of a calculation for normal-layout aircraft show that this method avoids the shortcomings of the rational function approximation method and is more accurate than the gust grouping method. Concurrently, gust aerodynamic force calculations were performed on aircraft with large aspect ratios and used in a real-time flight simulation. Full article

The paper proposes applying an in-house mathematical model of a liquid flat-plate solar collector to calculate the collector time constant. The described model, proposed for the first time in an earlier study, is a one-dimensional distributed parameter model enabling simulations of the collector operation under arbitrarily variable boundary conditions. The model is based on the solution of energy balance equations for all collector components. The formulated differential equations are solved iteratively using an implicit difference scheme. To obtain a stable numerical solution, it is necessary to use appropriate steps of time and spatial division. These were found by comparing the results obtained from the model with the results of the analytical solution available in the literature for the transient state, which constitutes the novelty of the present study. The accuracy of the results obtained from the model was verified experimentally by comparing the measured and calculated history of the fluid temperature at the outlet of the collector. The calculation of the collector time constant is proposed in the paper as an example of the model’s practical application. The results of the time constant calculation were compared with the values obtained experimentally on the test stand. This is another novelty of the presented research. The analysed collector instantaneous efficiency was then calculated for selected outdoor conditions. The presented mathematical model can also be used to verify the correctness of the collector operation. By comparing, on an ongoing basis, the measured and calculated values of the fluid temperature at the collector outlet, conclusions can be drawn about the process of solar glass fouling or glycol gelling. The simplicity of the model and the low computational demands enable such comparisons in an online mode. Full article

Background: The COVID-19 pandemic caused an unprecedented number of patients requiring veno-venous extracorporeal membrane oxygenation (VV ECMO) therapy. Clinical polyuria was observed at our ECMO center during the pandemic. This study aims to investigate the incidence, potential causes, and implications of polyuria in COVID-19 patients undergoing VV ECMO therapy. Methods: Here, 68 SARS-CoV-2 positive patients receiving VV ECMO were stratified into the following two groups: polyuria (PU), characterized by an average urine output of ≥3000 mL/day within seven days following initiation, and non-polyuria (NPU), defined by <3000 mL/day. Polyuria in ECMO patients occurred in 51.5% (n = 35) within seven days after ECMO initiation. No significant difference in mortality was observed between PU and NPU groups (60.0% vs. 60.6%). Differences were found in the fluid intake (p < 0.01) and balance within 24 h (p = 0.01), creatinine (p < 0.01), plasma osmolality (p = < 0.01), lactate (p < 0.01), urea (p < 0.01), and sodium levels (p < 0.01) between the groups. Plasma osmolality increased (p < 0.01) after ECMO initiation during the observation period. Results: Diuresis and plasma osmolality increased during VV ECMO treatment, while mortality was not affected by polyuria. Conclusions: Polyuria does not appear to impact mortality. Further investigations are warranted to elucidate its underlying mechanisms and clinical implications in the context of VV ECMO therapy and COVID-19 management. Full article

In the present study, we examined the inter-relationships between body water balance, nutritional risk, sarcopenia, and outcome after acute ischemic stroke (AIS) in patients who were living independently. We defined abnormal body water balance as overhydration, with an extracellular fluid/total body water ratio > 0.390. A geriatric nutritional risk index (GNRI) < 98 was considered low GNRI. Sarcopenia was defined according to the 2019 Asian Working Group for sarcopenia criteria. Poor outcome was defined as a modified Rankin scale (mRS) score ≥ 3 at discharge. Among 111 eligible patients (40 females, median age: 77 years), 43 had a poor prognosis, 31 exhibited overhydration, 25 had low GNRI, and 44 experienced sarcopenia. Patients with poor outcomes had significantly higher National Institutes of Health Stroke Scale (NIHSS) scores, which were significantly more common with overhydration, low GNRI, and sarcopenia (p < 0.001 for all). Concomitant overhydration, low GNRI, and sarcopenia were associated with poorer outcomes. In multivariate analysis, overhydration [odds ratio (OR) 5.504, 95% confidence interval (CI) 1.717–17.648; p = 0.004], age (OR 1.062, 95%CI 1.010–1.117; p = 0.020), and NIHSS score (OR 1.790, 95%CI 1.307–2.451; p < 0.001) were independent prognostic factors for poor outcome. The results indicated that the combination of overhydration, low GNRI, and sarcopenia predict poor outcomes following AIS. Overhydration was particularly associated with poor outcomes. Full article

The present study investigates the flow characteristics of fly ash-based (FA) geopolymers reinforced with polypropylene (PP) fibers during the extrusion process in three-dimensional printing. By applying the Herschel–Bulkley rheological model, this research provides a sound theoretical basis to understand the flow behavior of these materials under various conditions. The Herschel–Bulkley model describes the relationship between shear stress and the shear rate in non-Newtonian fluids, capturing yield stress and flow consistency. A combination of experimental and numerical techniques based on the Finite-Element Method (FEM) in COMSOL has been used in this study. The results of both experimental and simulation approaches are compared to examine the material behavior during extrusion. The experimental results indicate that PP fiber content significantly affects the rheological properties. Mixtures with high fiber content encountered issues such as high static yield. However, mixtures with moderate fiber content showed smoother extrusion processes, suggesting an optimal fiber addition range that balances mechanical properties and extrudability. The numerical simulations generally agreed with the experimental data up to a certain fiber content level, beyond which more complex interactions necessitate further model refinements. The investigation identified a 0.25% to 0.5% fiber content range that enhances performance without complicating the extrusion process, facilitating the production of properly printed structures. Full article

Reservoir damage is a key factor affecting reservoir evaluation, ensuring stable reservoir production and improving the utilization rate of oil and gas resources. At present, the evaluation of damage caused by reservoir drilling fluid is too empirical, and there is a lack of methods for the high-precision evaluation of reservoir damage after drilling fluid invasion and pollution. In a block in the East China Sea, the production capacity is limited due to an excessive balance of drilling fluid and long exposure time. In order to ensure safe drilling, the dynamic damage mechanism of drilling fluid during drilling was analyzed. The core of the main reservoir of well XH-1 in a block in the East China Sea was selected for carrying out an experiment evaluating the dynamic damage caused by drilling fluid. According to the experimental results, the damage rate of reservoir permeability caused by drilling fluid invasion ranges between 58.25 and 87.25%, and the overall dynamic damage degree can be classified between medium and high. Combined with the experimental parameters, a mathematical model of drilling fluid invasion depth was established, and the calculation formulas of drilling fluid invasion depth and contaminated skin were derived. The results showed that the drilling fluid depth of the reservoir section corresponding to the core of well XH-1 was 0.47~0.83 m, and the contaminated skin factor was 1.22~13.41, which made up for the lack of evaluation methods of reservoir damage caused by drilling fluid and provided a theoretical basis for the optimization of drilling fluid parameters and exploration drilling technology in oilfield operations. Full article

Fluid properties live at the heart of hydrocarbon reservoir engineering as it is related to the behavior of fluids under reservoir pressure depletion. To obtain their values, PVT experimental work needs to be performed. Although the experimental workflow is strictly defined, the accuracy of the measurements often suffers from significant errors which in turn affect severely all the following engineering calculations as well as the following equation of state (EoS) tuning step. In this work, a systematic methodology is developed to apply quality control (QC) on the PVT values reported in a typical lab report. Firstly, the equations expressing mass balance are developed to calculate the missing closing data, such as the residual oil density and the composition of oil collected at each stage of the depletion study. Subsequently, computational tools are developed to evaluate the physical soundness of the received results and provide insight as to whether the quality of the experimental data is sufficient. To demonstrate the proposed workflow, it is applied to a selection of representative reservoir fluids of varying volatility. We demonstrate that depending on the reservoir fluid properties, calculations may yield highly unrealistic results, which engineers should avoid using unless corrected. Specifically, differential liberation (DL) test properties reported for low-volatility oils are generally reliable. However, for high-volatility oils, particularly during the final depletion stages, the test outcomes often become unrealistic. Finally, instructions to fluid and reservoir engineers on how to handle those issues and protect the reliability of their calculations are provided. Full article

The water-impacting behavior of a wedge is often studied in the slamming phenomenon of ships and aircraft. Many scholars have proposed theoretical models for studying the water-impacting problem of a wedge, but these models still have some shortcomings. This study combines Von Karman’s method, the Generalized Wagner Model (GWM), and Modified Logvinovich Model (MLM) to establish a converged theoretical Von Karman-GWM-MLM (VGM) model. The VGM model utilizes added mass to replace the fluid influence, which is derived from the velocity potential and boundary conditions. Considering the influence of impulse, the velocity is determined by the momentum theorem. Subsequently, the pressure, resultant force, and acceleration of the wedge can be calculated. By comparing with the published test data of other scholars, it is found that the velocity, acceleration, pressure, and force of the wedge obtained by the VGM model reached a consensus with experiments. The validity and accuracy of the VGM model are also verified. The efficiency and accuracy of problem-solving are both balanced when using the VGM model. The establishment of the VGM model is significant for solving water-impacting problems related to wedges. Full article

After polymer flooding, the heterogeneity between different layers intensifies, forming intricate seepage channels and fluid diversions, which results in decreased circulation efficiency and lower recovery rates, leaving a significant amount of residual oil trapped within the reservoir. Understanding the characteristics of residual oil occurrence is crucial for enhancing oil recovery post-polymer flooding. This study focused on sandstone reservoirs with varying permeability in the Saertu block of the Daqing oilfield. Using cryosectioning and laser scanning confocal microscopy, the occurrence characteristics of the residual oil in these sandstone reservoirs post-polymer flooding were investigated. Additionally, micro-CT and scanning electron microscopy were employed to analyze the impact of the pore structure on the distribution characteristics of the residual oil. The results indicate that laser scanning confocal images reveal that post-polymer flooding, the residual oil in high- and low-permeability sandstone reservoirs predominantly exists in a bound state (average > 47%), mostly as particle-adsorbed oil. In contrast, the residual oil in medium-permeability reservoirs is primarily in a free state (average > 49%), mostly as intergranular-adsorbed oil. In high-permeability sandstone reservoirs, heavy oil components are mainly in a particle-adsorbed form; in medium-permeability sandstone reservoirs, residual oil predominantly consists of heavy components, with most light components occurring in a clustered form; in low-permeability sandstone reservoirs, clustered residual oil exists in a balanced coexistence of light and heavy components, while the heavy components primarily exist in a particle-adsorbed form. Post-polymer flooding, the large pore–throat structure in high-permeability sandstone reservoirs results in effective displacement and less free residual oil; medium-permeability sandstone reservoirs, with medium–large pores and throats, have preferential channels and fine particles blocking the throats, leading to some unswept pores and more free residual oil; low-permeability sandstone reservoirs, with small pores and throats, exhibit weak displacement forces and poor mobility, resulting in more bound residual oil. The distribution and content of clay particles and clay minerals, along with the complex microscopic pore structure, are the main factors causing the differences in the residual oil occurrence states in sandstones with varying permeability. Full article

Making rate transient analysis (RTA) and formation evaluation for multi-fractured tight gas wells has always been a difficult problem. This is because the fluid flow in the formation has multiple nonlinear flow mechanisms, including gas-water two-phase flow, gas slippage, low-velocity non-Darcy flow, and stress-dependent permeability. In this paper, a novel RTA method is proposed for multi-fractured wells in tight gas reservoirs incorporating nonlinear flow mechanisms. The RTA method is based on an analytical model, which is modified from the classical trilinear flow model by considering all the nonlinear flow mechanisms. The concept of material balance time and normalized rate is used to process the production data for both water and gas phases. The techniques of approximate solutions in linear/bilinear flow regimes and type curve fitting are combined in the proposed RTA method. After that, the rate transient behaviors and influencing factors of multi-fractured tight gas wells are analyzed. A field case from Northwestern China is used to test the efficiency and practicability of the proposed RTA method. The results show that six flow regimes for both gas and water production performances are exhibited on the log-log plots of normalized production rate against material balance time. The rate transient responses are sensitive to the nonlinear flow mechanisms, and formation and fracture properties. The medium flow regimes are significantly affected by fracture number, fracture conductivity, fracture half-length, stress-dependent permeability, gas-water two-phase flow, and formation permeability, which should be considered in making RTA of fractured tight gas wells. The field case shows that both gas and water production performances can be well-fitted using the proposed RTA method. The major innovation of this paper is that a novel RTA method is proposed for fractured tight gas wells considering multiple nonlinear flow mechanisms, and it can be used to make reasonable formation and fracturing evaluations in the field. Full article

The state of well-being and health of our body is regulated by the fine osmotic and biochemical balance established between the cells of the different tissues, organs, and systems. Specific districts of the human body are defined, kept in the correct state of functioning, and, therefore, protected from exogenous or endogenous insults of both mechanical, physical, and biological nature by the presence of different barrier systems. In addition to the placental barrier, which even acts as a linker between two different organisms, the mother and the fetus, all human body barriers, including the blood–brain barrier (BBB), blood–retinal barrier, blood–nerve barrier, blood–lymph barrier, and blood–cerebrospinal fluid barrier, operate to maintain the physiological homeostasis within tissues and organs. From a pharmaceutical point of view, the most challenging is undoubtedly the BBB, since its presence notably complicates the treatment of brain disorders. BBB action can impair the delivery of chemical drugs and biopharmaceuticals into the brain, reducing their therapeutic efficacy and/or increasing their unwanted bioaccumulation in the surrounding healthy tissues. Recent nanotechnological innovation provides advanced biomaterials and ad hoc customized engineering and functionalization methods able to assist in brain-targeted drug delivery. In this context, lipid nanocarriers, including both synthetic (liposomes, solid lipid nanoparticles, nanoemulsions, nanostructured lipid carriers, niosomes, proniosomes, and cubosomes) and cell-derived ones (extracellular vesicles and cell membrane-derived nanocarriers), are considered one of the most successful brain delivery systems due to their reasonable biocompatibility and ability to cross the BBB. This review aims to provide a complete and up-to-date point of view on the efficacy of the most varied lipid carriers, whether FDA-approved, involved in clinical trials, or used in in vitro or in vivo studies, for the treatment of inflammatory, cancerous, or infectious brain diseases. Full article

Background: The surgical treatment of advanced ovarian cancer is associated with extensive tissue trauma, prolonged operating times and a considerable volume shift. It, therefore, represents a challenge for anaesthesiological management. Aim: The aim of this single-centre, retrospective, observational study was to investigate whether intraoperative extensive volume supply influences postoperative outcomes and long-term survival. Methods: The study included 73 patients with a mean (SD) age of 63 (13) years who underwent extensive tumour-reducing surgery for ovarian cancer between 2012 and 2015. The effect of the intraoperative fluid balance on postoperative complications, such as anastomotic insufficiency or pleural effusions, was investigated using logistic regression. Further, the influence of fluid balance, lactate and creatinine levels on 5-year survival was analysed in a Cox regression model. Associations between anaesthesia time and the intraoperative fluid balance were examined using Spearman’s rank correlation coefficients. Results: The mean (SD) postoperative fluid balance in the considered patient cohort was 9.1 (3.4) litres (l) at a mean (SD) anaesthesia time of 529 (106) minutes. Cox regression did not reveal a statistically significant effect of the fluid balance, but it did reveal a statistically significant association between the lactate level 24 h following surgery and the 5-year survival (HR [95%-CI] fluid balance: 0.97 [0.85, 1.11]; HR [95%-CI] lactate: 1.79 [1.24, 2.58]). According to logistic regression, the intraoperative fluid balance was associated with an increased chance of postoperative complications in the considered patient cohort (OR [95%-CI] 1.28 [1.1, 1.54]). Conclusions: We could not detect a negative impact of an increased fluid balance on 5-year survival, but a negative impact on postoperative complications was found in our patient cohort. Full article