Search Results (63)

Introduction: In recent years, a greater number of adults have been undergoing spinal surgery. The main complications in the postanesthetic care unit (PACU) include respiratory and cardiovascular problems, pain, and nausea or vomiting. The aim of this study was to describe the preoperative characteristics and intra-anesthetic management of adult patients who underwent elective spinal surgery with balanced general anesthesia and to identify the predictive factors associated with supplemental oxygen requirement upon discharge from the PACU. In addition, we sought to develop a risk index on the basis of multivariable analysis allowing stratification of the probability of supplemental oxygen requirement upon discharge from the PACU. Materials and Methods: In this cross-sectional, retrospective, observational study, the pre- and intra-anesthetic characteristics of adult patients who underwent spinal surgery at any vertebral level under balanced general anesthesia in a tertiary hospital were retrieved. Descriptive statistics are provided, and comparison (Kruskal–Wallis) or correlation analyses (chi-square) were conducted between the characteristics of the patients grouped according to the need for supplemental oxygen upon discharge from the PACU. Receiver operating characteristic (ROC) curves and a multivariate logistic regression model were generated. All tests were performed at the α = 0.05 level. Results: Among 349 patients initially considered, only 211 were included in the analysis. A total of 45.50% of the patients who underwent spinal surgery under balanced general anesthesia required supplemental oxygen upon discharge from the PACU; these patients had significantly greater age, body mass index (BMI), surgery time, and anesthesia time. In addition, the use of norepinephrine and the use of fentanyl were associated with the need for supplemental oxygen. Our proposed risk index for predicting the need for supplemental oxygen upon discharge from the PACU, according to the implementation of a multivariable logistic model based on three simple variables (age ≥ 48 years, BMI ≥ 26.5, and use of fentanyl infusion), achieved an area under the curve (AUC) of 0.740. Conclusions: Age, BMI, and the use of fentanyl can be used to predict the need for supplemental oxygen upon discharge from the PACU. Multicenter and/or longitudinal studies with large sample sizes are needed to confirm the results of this study and improve the prediction of the need for supplemental oxygen upon discharge from the PACU. Full article

The growing demand for sustainable water management solutions has prompted the development of membrane brine concentration (MBC) technologies, particularly in the context of desalination and minimum liquid discharge (MLD) applications. This study presents a simple model of high-pressure nanofiltration (HPNF) for MBC. The model integrates reverse osmosis (RO) transport equations with mass balance equations, thereby enabling acceptable predictions of water flux and total dissolved solids (TDS) concentration. Considering the limitations of the pilot plant data, the model showed reasonable accuracy in predicting flux and TDS, with R² values above 0.99. The simulation results demonstrated that an increase in feed flow rate improves flux but raises specific energy consumption (SEC) and reduces recovery. In contrast, an increase in feed pressure results in an increased recovery and brine concentration. Increasing feed TDS decreases flux, recovery, and final brine TDS and increases SEC. Response surface methodology (RSM) was employed to optimize process performance across multiple criteria, optimizing flux, SEC, recovery, and final brine concentration. The optimal feed flow rate and pressure vary depending on the criteria in the improvement scenarios, underscoring the importance of systematic process improvement. Full article

Urban areas present different climates from those of their rural surroundings. Energy balance and especially energy storage play important roles in the resulting climate since more than 50% of the net radiation is absorbed in densely urbanized areas. A simple model of energy storage in the urban fabric is presented, fed with the air temperature of a given area and its thermal properties; it can estimate heat storage (Q_S) with good results. The proposed Q_ST energy storage model was compared with Q_S results obtained from two sites in Mexico City, Escandón (objective hysteresis model, Q_SOHM) and ENP7 (residual, Q_SRES), and one site in Marseille, France (thermal mass scheme, Q_STMS). The comparison between Q_ST and Q_SOHM showed that r² = 0.71, while in ENP7 (Q_N > 0), Q_SRES and Q_ST were 116.5 Wm⁻² and 142 Wm⁻², corresponding to 49% and 60% of the Q_N, respectively. The results obtained using the Q_STMS model in Marseille and Q_ST in Escandón showed similar behavior, with RMSEs of 109 and 101 Wm⁻², respectively, in a daily period. Although it is difficult to discern which method is better, it is possible to affirm that the presented method is quite accurate, easier to use, and inexpensive. Full article

Background/Objectives: Resting metabolic rate (RMR) is an important contributor of energy balance and displays a well-documented relationship with sex, age, race and fat-free mass (FFM) in the existing scientific literature. However, the impact of other body composition components such as fat and liver fat on RMR remains unclear. This study aims to investigate the correlation of RMR with body composition parameters in a sample of patients with overweight and obesity. Methods: Retrospective data of patients with overweight or obesity referred for magnetic resonance imaging of liver fat during the period 2018–2023 were utilized for this study. Demographic and anthropometric data were collected, including body composition parameters (body fat, muscle mass) and RMR measured by bioelectrical impedance and indirect calorimetry, respectively. Results: The final sample included 53 patients (66% male), with a mean age of 48 years (±11.2) and a mean body mass index (ΒΜΙ) of 38.5 kg/m² (32.7, 44.7). Simple correlation models revealed that RMR was separately correlated with gender, age, BMI, muscle mass, and liver fat (all p < 0.05) but not with fat mass. When multiple regression models were employed, only muscle mass retained its statistically significant influence on RMR, while total and hepatic fat did not significantly affect RMR after controlling for other parameters (gender, age, muscle mass). Conclusions: These findings confirm the known correlation between muscle mass and RMR while highlighting the lack of association between total and hepatic fat and RMR in individuals with overweight and obesity. Full article

Installation of flat solar collectors (FSCs) has been increasing due to the zero cost of renewable energy. However, the performance of this equipment is limited by the area, the material and the thermophysical properties of the working fluid. To improve the properties of the fluid, metal and metal oxide nanoparticles have mainly been used. This paper presents the performance assessment of the FSCs using simple and hybrid carbon nanofluids of low thermal capacity. Energy and mass balance modeling was performed for this study. A parametric analysis was conducted to examine the impact of key variables on the performance of the solar collectors using simple graphite and fullerene nanofluids, as well as hybrid metal–oxide–carbon nanofluids. From the results of heat transfer in FSCs, using graphite and fullerene nanofluids, it can be concluded that adding these nanoparticles improves the convection coefficient by 40% and 30%, respectively, with 10% nanoparticles. The graphite and fullerene nanoparticles can enhance the efficiency of FSCs by 2% and 1.5% more than base fluid. As the decrease in efficiency using fullerene with magnesium oxide is less than 0.2%, fullerene hybrid nanofluids could still be used in FSCs. Full article

Controlled environment agriculture is a promising alternative to conventional production methods, as it is less affected by climate change and is often more sustainable, especially in circular and recycling frameworks such as aquaponics. A major cost factor in such facilities, however, is the need for skilled labor. Depending on available resources, there are endless possibilities on how to choose ingredients to realize a desired nutrient solution. At the same time, the composition of the desired solution is subject to fluctuations in fish water quality, fertilizer availability, weather, and plant development. In high-evaporation scenarios, e.g., summer, nutrient solutions might be mixed multiple times per day. This results in a complex, multi-variable task that is time-consuming to solve manually, yet requires frequent resolution. This work aims to help solve this challenge by providing methods to automate the nutrient mixing procedure. A simple mass-balance-based model of a nutrient mixing tank with connections to different water sources, drains, and fertilizers is provided. Using methods of static optimization, a program was developed which, in consideration of various process constraints and optimization variables, is able to calculate the necessary steps to mix the desired solution. The program code is provided in an open-source repository. The flexibility of the method is demonstrated in simulation scenarios. The program is easy to use and to adapt, and all necessary steps are explained in this paper. This work contributes to a higher automation level in CEA. Full article

The paper describes the implementation of internal boundary conditions in the 1D ORSADEM hydraulic model to simulate the effect of a hydraulic in-line structure. The proposed model introduces a simplified representation of the bridge geometry by imposing an equivalent narrowing, computed according to the opening size and characteristics, combined with the mass and energy balance at the structure. The model is then applied to a series of experimental tests concerning the propagation of shock waves through different types of bridges, representing different flow conditions, from free surface flow to overflow. The tests are also simulated with the original 1D ORSADEM model, including the standard head losses and the cross-section narrowing due to the presence of a structure. The comparison with the experimental measurements shows that the proposed model can simulate the shock wave flow through the bridges with a higher accuracy than the standard formulation. These findings highlight the possibility of properly evaluating the backwater effect at bridges even with a simple 1D model if the physical narrowing of the cross-section is modeled. Full article

Hydrological modeling can be challenging due to significant data requirements and computational complexities. Hydrological models must be sufficiently complex to describe physical processes yet simple enough to use. This paper describes the development of a simplified watershed-scale input–output model to simulate runoff quantity and quality during a storm event. This work builds upon an existing semi-distributed rainfall–runoff model by adding calculations for pollutant concentrations based on simplified mass balance equations. The model was tested against various watershed examples of increasing complexity. The results show the change in peak flow and pollutant concentration in different areas of the watershed, demonstrating the model’s ability to account for the dynamics of runoff movement through the watershed. This paper advances watershed management by addressing data scarcity through the development of a simplified hydrological model that effectively incorporates spatial variability within a watershed while requiring minimal data input. Full article

Industrial ball milling circuits usually include hydrocyclones in a closed configuration to achieve a specified grinding size. Although hydrocyclones are relatively simple to operate, their classification performance is generally low, leading to significant fines recirculation within the circuit, consequently overgrinding the product. Conversely, high-frequency screening potentially shows a relatively higher separation efficiency, as the entrainment of fines to the coarse product is significantly reduced. The present work compares the performance of hydrocyclones—HC and high-frequency screens—HFS based on four surveys conducted in Nexa’s Vazante Zinc ore industrial grinding circuit in Vazante, Brazil, which processes zinc silicate ore. The comparisons included the partition of solids, water split, and particle size distributions. Whiten’s partition curve model was adopted to obtain the selected performance parameters through mass balancing the experimental data. The industrial surveys comprised three different size separation configurations, i.e., HC-Only, HFS-Only, and a combined HC-HFS setup. In all cases, the assessments consistently indicated higher separation performances with HFS compared to the HC operation. The final product associated with the HC+HFS configuration showed a narrower size distribution around the grinding size. Full article

A simple predictive analytical model for induction times in reverse osmosis (RO), both with and without an antiscalant (AS), has been developed based on the fundamental principles of mass and momentum balance. The simplicity of the model arises from the very low Reynolds number in the vicinity of the cluster surface, enabling the use and derivation of exact equations. The main assumption of the induction time without AS, t_0A, is that the net growth of the cluster size results from the difference between adhesion and shear forces. With AS, the induction time, t_A, is extended due to the competition between the AS and the scaling molecules on the cluster’s surface ligands. The model was validated by fitting it to six independent datasets from experiments conducted with spiral-wound and tubular RO membranes under various operational conditions, resulting in an average difference of 8.0% (t_0A) and 8.7% (t_A) between predicted and experimental induction times. It was found that t_0A is governed by three dimensionless parameters: supersaturation ratio (S_a), shear (K_u), and scalant saturation (κ). t_A increases with t_0A and the AS concentration. Full article

Approximate models are a fast and most often precise tool for determining the effectiveness factor for heterogeneous catalysis processes that are realized in the real world. They are also frequently applied as robust transient models describing the work of a single catalyst pellet or as a part of a more complex model, for example, a reactor model, where mass balances for the gas phase and solid phase are necessary. So far, approximate models for diffusion and reaction processes have been presented for processes described by a single balance equation. In the present work, approximate models without the mentioned limitation are presented and discussed. In addition, simple rules are shown for the development of other complex approximate models without tedious derivation in the complex domain. The formulas considered in this work are typical long-time approximations of the transient process. The accuracy is good, especially in the range of small and intermediate Thiele modulus values. Full article

The genome-scale metabolic model (GSMM) of Cordyceps militaris provides a comprehensive basis of carbon assimilation for cell growth and metabolite production. However, the model with a simple mass balance concept shows limited capability to probe the metabolic responses of C. militaris under light exposure. This study, therefore, employed the transcriptome-integrated GSMM approach to extend the investigation of C. militaris’s metabolism under light conditions. Through the gene inactivity moderated by metabolism and expression (GIMME) framework, the iPS1474-tiGSMM model was furnished with the transcriptome data, thus providing a simulation that described reasonably well the metabolic responses underlying the phenotypic observation of C. militaris under the particular light conditions. The iPS1474-tiGSMM obviously showed an improved prediction of metabolic fluxes in correlation with the expressed genes involved in the cordycepin and carotenoid biosynthetic pathways under the sucrose culturing conditions. Further analysis of reporter metabolites suggested that the central carbon, purine, and fatty acid metabolisms towards carotenoid biosynthesis were the predominant metabolic processes responsible in light conditions. This finding highlights the key responsive processes enabling the acclimatization of C. militaris metabolism in varying light conditions. This study provides a valuable perspective on manipulating metabolic genes and fluxes towards the target metabolite production of C. militaris. Full article

This article aims to develop a method to automatically generate CFD-based compartment models. This effort to simplify mixing models aims at capturing the interactions between material transport and chemical/biochemical conversions in large-scale reactors. The proposed method converts the CFD results into a system of mass balance equations for each defined component. The compartmentalization method is applied to two bioreactor geometries and was able to replicate tracer mixing profiles observed in CFD simulations. The generated compartment models were successfully coupled with, a simple Monod-type biokinetic model describing microbial growth, substrate consumption and product formation. The coupled model was used to simulate a four-hour fermentation in a 190 L reactor and a 10 ${\mathrm{m}}^3$ reactor. Resolving the substrate gradients had a clear impact on the biokinetics, increasing with the scale of the reactor. Moreover, the coupled model could simulate the fermentation faster than real-time. Having a real-time-solvable model is essential for implementations in digital twins and other real-time applications using the models as predictive tools. Full article

The motion of a heavy mass on a bridge span causes vibrations whose magnitude and frequency content depend on the mechanical properties of the structural system, including the magnitude of that mass and its speed of traverse. In order to limit vibrations that could potentially cause damage, a simple passive device configuration, namely the tuned mass damper (TMD), is introduced and its effect on the beam vibrations analyzed. Specifically, a TMD in the form of a single-degree-of-freedom (SDOF) unit comprising a mass and a spring is placed on the span to act as a secondary system for absorbing vibrations from the primary system, i.e., the bridge itself. A Lagrangian energy balance formulation is used to derive the governing equations of motion, followed by an analytical solution using the Laplace transform to investigate the transmission of vibratory energy between primary and secondary systems. Results are given in terms of time histories, Fourier spectra and spectrograms, where the influence of the TMD in reducing vibratory energy is demonstrated. The TMD is placed in the region where the beam’s transverse motion is at a maximum, while its mechanical properties are sub-optimal, in the sense that there is no separate damper present and minimal damping is provided by the spring element itself. In parallel with the analysis, a series of experiments involving a simply supported model steel bridge span traversed by a heavy mass are conducted to first gauge the analytical solution and then to confirm the validity of the proposed passive scheme. Full article

Research focusing on energy, water vapor, and CO₂ exchanges over the Caatinga Biome is recent. Consequently, there exist research gaps on this topic that limit our ability to understand and project interannual and long-term variations in the CO₂ cycle of this environment. Thus, the objective of this study was to evaluate the behavior of the energy and CO₂ balances of the Caatinga Biome under extreme rainfall conditions (extreme drought and intense rainfall) using simulations of the SITE model (Simple Tropical Ecosystem Model). Meteorological data from the years 2009 (heavy rainfall) and 2012 (extreme drought) obtained from an INMET automatic station were used. Relationships between monthly GPP and NEE values and rainfall were also analyzed. Although the SITE model had been previously calibrated for the region, adjustments to the calibration were necessary for our study due to the extreme climatic values of the selected years. The results highlight the impact of rainfall on energy and mass exchanges over the Caatinga, particularly evident in the partitioning of the energy balance and the CO₂ balance. In 2009 (during heavy rainfall), the fraction of Rn converted into LE was nearly 6% higher compared to the values observed in 2012 (during extreme drought). Regarding CO₂, it was found that the Caatinga behaved as a sink, even under extreme drought conditions (2012), with annual average values of −1.86 µmol m⁻² s⁻¹ (2009) and −0.81 µmol m⁻² s⁻¹ (2012). Relationships between monthly GPP and NEE values and rainfall were also investigated, revealing an asymptotic relationship between the components of CO₂ balance and rainfall. It was evident that both the monthly values of GPP and NEE tend to stabilize when monthly rainfall volumes exceed 200 mm. Full article