Search Results (6,232)

Let M be an Abelian monoid. A necessary and sufficient condition for the class $\mathcal{A}r{m}_M$ of all Armendariz rings relative to M to coincide with the class $\mathcal{A}rm$ of all Armendariz rings is given. As a consequence, we prove that $\mathcal{A}r{m}_M$ has exactly three cases: the empty set, $\mathcal{A}rm$, and the class of all rings. If N is an Abelian monoid, then we prove that $\mathcal{A}r{m}_{M\times N}=\mathcal{A}r{m}_M\bigcap \mathcal{A}r{m}_N$, which gives a partial affirmative answer to the open question of Liu in 2005 (whether R is $M\times N$-Armendariz if R is M-Armendariz and N-Armendariz). We also show that the other Armendariz-like rings relative to an Abelian monoid, such as M-quasi-Armendariz rings, skew M-Armendariz rings, weak M-Armendariz rings, M-$\pi$-Armendariz rings, nil M-Armendariz rings, upper nil M-Armendariz rings and lower nil M-Armendariz rings can be handled similarly. Some conclusions on these classes have, therefore, been generalized using these classifications. Full article

After the COVID-19 lockdown, the health authorities established strict protocols for ventilating indoor spaces and reducing contagion. Although the control of the disease allowed these measures to be relaxed, indoor air quality (IAQ) and natural ventilation (NV) are still essential. However, in certain climatic conditions, this can affect the thermal comfort of the occupants. This situation is relevant in educational buildings, where thermal discomfort can influence students’ academic performance, especially during critical periods such as exams. In this context, this article explores how different NV strategies, both during and after the pandemic, affect the thermal comfort of students at a university in a Mediterranean climate zone. The analyses revealed that, despite the low temperatures and strict ventilation protocols due to COVID-19, thermal comfort during winter was higher than in spring and summer. These results led to an investigation into which variables could explain this phenomenon, detecting that the choice of clothing was crucial to achieving adequate comfort conditions. Regarding IAQ, ventilation was sufficient, even excessive, in some cases, especially during mandatory measures. In conclusion, it would be beneficial to establish ventilation protocols adapted to each environment and to advise students on individual strategies to improve their thermal comfort. Full article

The transition from conventional soil mapping (CSM) to digital soil mapping (DSM) not only affects the final map products, but it also affects the concepts of scale, resolution, and sampling intensity. This is critical because in the CSM approach, sampling intensity is intricately linked to the desired scale of soil map publication, which provided standardization of sampling. This is not the case for DSM where sample size varies widely by project, and sampling design studies have largely focused on where to sample without due consideration for sample size. Using a regional soil survey dataset with 1791 sampled and described soil profiles, we first extracted an external validation dataset using the conditioned Latin hypercube sampling (cLHS) algorithm and then created repeated (n = 10) sample plans of increasing size from the remaining calibration sites using the cLHS, feature space coverage sampling (FSCS), and simple random sampling (SRS). We then trained random forest (RF) models for four soil properties: pH, CEC, clay content, and SOC at five different depths. We identified the effective sample size based on the model learning curves and compared it to the optimal sample size determined from the Jensen–Shannon divergence (D_JS) applied to the environmental covariates. Maps were then generated from models that used all the calibration points (reference maps) and from models that used the optimal sample size (optimal maps) for comparison. Our findings revealed that the optimal sample sizes based on the D_JS analysis were closely aligned with the effective sample sizes from the model learning curves (815 for cLHS, 832 for FSCS, and 847 for SRS). Furthermore, the comparison of the optimal maps to the reference maps showed little difference in the global statistics (concordance correlation coefficient and root mean square error) and spatial trends of the data, confirming that the optimal sample size was sufficient for creating predictions of similar accuracy to the full calibration dataset. Finally, we conclude that the Ottawa soil survey project could have saved between CAD 330,500 and CAD 374,000 (CAD = Canadian dollars) if the determination of optimal sample size tools presented herein existed during the project planning phase. This clearly illustrates the need for additional research in determining an optimal sample size for DSM and demonstrates that operationalization of DSM in public institutions requires a sound scientific basis for determining sample size. Full article

A fault-tolerant collaborative control strategy for four-wheel-drive electric vehicles is proposed to address hidden safety issues caused by one or more in-wheel motor faults; the basic design scheme is that the control system is divided into two layers of motion tracking and torque distribution, and three systems, including driving, braking, and front-wheel steering are controlled collaboratively for four-wheel torque distribution. In the layer of motion tracking, a vehicle model with two-degree-of-freedom is employed to predict the control reference values of the longitudinal force and additional yaw moment required; four types of sensors, such as wheel speed, acceleration, gyroscope, and steering wheel angle, are used to calculate the actual values. At the torque distribution layer, SSOD and MSCD distribution schemes are designed to cope with two operating conditions, namely sufficient and insufficient output capacity after local hub motor failure, respectively, focusing on the objective function, constraints, and control variables of the MSCD control strategy. Finally, two operating environments, a straight-line track, and a DLC track, are set up to verify the effectiveness of the proposed control method. The results indicate that, compared with traditional methods, the average errors of the center of mass sideslip angle and yaw rate are reduced by at least 12.9% and 5.88%, respectively, in the straight-line track environment. In the DLC track environment, the average errors of the center of mass sideslip angle and yaw rate are reduced by at least 6% and 4.5%, respectively. The proposed fault-tolerant controller ensures that the four-wheel-drive electric vehicle meets the requirements of handling stability and safety under one or more hub motor failure conditions. Full article

This study assessed the status of water, sanitation, and hygiene (WASH) services at (49) selected primary schools in uMfolozi Local Municipality, which is situated in the province of Kwa-Zulu Natal in South Africa. Data were collected using an observational checklist tool and by conducting a walk-through survey to inspect the conditions of sanitary facilities, observe the hand-washing practices of the school learners, and analyse the accessibility to safe drinking water in school premises. The data were analysed with the Statistical Package for Social Science Version 29. This study revealed that there is easy access to safe drinking water in all but one school. The dependability of the water supply seemed to be one of the most urgent problems in every school, even though all of them have some kind of drinking water infrastructure on their grounds. Municipal water (n = 25, 36%) and rainwater (n = 25, 36%) were the most common type of water used in schools compared to borehole (n = 15, 22%) and tanker truck water (n = 4, 6%). Schools must have a reserved water supply because of the inconsistent supply of municipal water, and because rainwater is a seasonal harvest while borehole water may be affected by factors like load-shedding. The UNICEF-described ratio of one tap or disperser per fifty learners suggests that the water taps in the schoolyard were insufficient in some schools (n = 25, 36%). Rainwater is collected through a gutter system in the school building roofs and stored in 5000–10,000 Jojo tanks. Borehole water is pumped into Jojo tanks at an elevated position where it is stored, and learners receive the water through taps connected to the borehole tanks. During an emergency when there is no water supply from other sources, tanker trucks are hired to fill tanks that are also used to store rainwater. The borehole and rainwater quality appeared to be clear, but water treatment had not been performed, and the microbial quality was unknown. This shows that the Sustainable Development Goal (SGD) 6, clean water and sanitation, is still far from being met. According to national norms and standards for domestic water and sanitation services, people who do not use water treatment or purification techniques fall in the ‘no service’ category and contribute to the water backlog. Pit latrines (n = 46, 94%) and flush toilet (n = 3, 6%) were found to be the only convenient toilet systems used. The number of toilets is not sufficient according to the guidelines. There are (n = 46, 94%) of the schools in the study area using pit latrine due to insufficient or no water supply. In 89.8% of primary schools, sanitation facilities are in working condition in terms of repair and hygiene, while 10.2% are not usable in terms of hygiene, and these are mostly boy’s toilets. All schools (n = 46, 94%) that have flush toilets is because they received sponsorship from non-government stakeholders that funded them in achieving piped water systems that permit the functionality of flush toilets. For the purposes of this study, hygiene was evaluate based on the items found in toilets and handwashing practices. The hygiene aspects of toilets included tissues, cleanness, and toilet seat. For handwashing practices we looked the number of washing basins, the colour of water, and having soaps to use. In the schools that did provide handwashing facilities, some of the toilets were broken, there was no water, or there was no drainage system in place to allow them to function. However, according to the school act, the handwash basins should be inside the facilities. A total of (n = 7, 14%) of handwash basins were inside the toilets. Only (n = 2, 4%) of schools had handwashing facilities which were Jojo tanks with taps near toilets, which were outside of the toilet, with no soap provided. Additionally, (n = 40, 82%) of learners used drinking points for handwashing, which can possibly transmit microbes among them. The findings revealed that, in general, (n = 32, 64%) of school toilets were clean, while, in general, the girls’ toilets were cleaner than the boys’ toilets. In all the schools, the cleaning services were from the people who were involved in school nutrition. In conclusion, there were water sources available for access to water inside schools; however, the situation can be improved by increasing the number of water source points. Pit latrines were the main used toilets, which were in a majority of the schools, and did not have the necessary terms for hygiene such as handwashing basin, tissues, and others. The lack of the main aspect, i.e., access to water and sanitation items, results in an impact on hygiene to learners as they will fail to practice proper hygiene. However, improvement can still be made by keeping the boys’ toilets clean while increasing the number of handwashing basins inside the toilets, so that they do not use taps outside the toilets. Schools should work towards meeting the required number of handwashing basins to increase access to handwashing facilities. Full article

This paper offers new insights into gravitational interactions within a general non-inertial reference frame. By utilizing symbolic tensor calculus, the study establishes a unified framework that connects time derivatives in non-inertial frames to those in inertial frames. The research introduces new first integrals of motion for a system of many particles in arbitrary non-inertial and barycentric rotating reference frames. These first integrals provide a kinematic and geometric visualization of motion in non-inertial frames. Additionally, a generalized potential energy function is presented for broader applicability. For the gravitational two-body problem, the paper delivers a closed-form, coordinate-free solution for the motion of each body relative to the original frame. Consequently, sufficient conditions for stability against collisions are established within the context of the two-body problem in a non-inertial reference frame. Furthermore, the paper examines the relative orbital motion of spacecraft, presenting a closed-form and coordinate-free solution in the local vertical local horizontal (LVLH) non-inertial frame, which is centered on the center of mass of the main spacecraft. Full article

In recent years, wind power has become a more attractive alternative energy source for overcoming environmental issues. Predictive maintenance is essential for wind power devices to ensure that these systems work reliably and with sufficient availability. This paper presents a method to work around failure detection in wind turbines using the sound emitted from their components. The proposed Artificial Intelligence (AI) model is based on unsupervised learning and image processing, through which the machine learning model learns to identify spectrograms from wind turbines under healthy conditions. The reconstruction of current data determines whether the input data have an uncommon noise, which translates into a possibility of failure or an effective one. The uncommon data are sent to a specialist network, which, through supervising learning, identifies a failure event and alerts operators to possible problems that the wind turbine could pass through, helping with preventive maintenance. The model offered satisfactory results in five tested wind turbines, in which some specific faults known by the operators were captured through the low similarity between the reconstructed data and the input. Additionally, this application could be extended to similar applications in industrial machinery within the scope of audible noises in rotative machine mechanisms. Full article

CO₂-enhanced gas recovery (EGR) has emerged as a promising method for improving hydrocarbon production and achieving carbon sequestration in offshore gas reservoirs. This study investigates the performance and influencing factors of CO₂-based gas displacement using long core displacement experiments. Consolidated synthetic cores were prepared to replicate reservoir conditions, and experiments were conducted at formation pressure and temperature to evaluate the effects of permeability, injection pressure, CO₂ concentration, and core length on gas recovery efficiency. The results reveal that (1) for a homogeneous porous medium, permeability and injection pressure have minimal correlation with recovery efficiency when sufficient gas is injected; (2) direct gas displacement after reservoir depletion outperforms pressure-boosting displacement methods; (3) higher CO₂ concentrations delay gas breakthrough, enhance piston-like displacement behavior, and improve recovery efficiency; and (4) core length significantly affects recovery, with longer cores resulting in slower breakthroughs and more stable displacement. Cores of at least 1 m in length are essential for accurately simulating field conditions. For a CO₂ injection with a pressure of 7 MPa and a temperature of 81 °C, when 0.87 PV of CO₂ is injected, the current recovery can reach 87%, after which the displacement efficiency decreases sharply. The ultimate EGR can be as high as 50%. These findings provide valuable insights into optimizing CO₂ injection strategies for enhanced gas recovery in offshore reservoirs, offering guidance for both experimental designs and practical applications in the field. Full article

To compare them with PTFE-40# steel tribo-pairs, the tribological properties of textured PEEK-40# (AISI 1040) steel friction pairs were researched under full-film lubrication conditions by manufacturing micro-dimples with different dimensions on the contact surfaces of 1040 steel discs using laser surface texturing (LST). After repeated tribological tests, the coefficients of friction (COFs), wear losses, and wear morphologies of the PEEK-1040 steel friction pairs were measured and analyzed. The results show that micro-dimples do not significantly reduce the average COFs of PEEK-1040 steel friction pairs when lubricated with a sufficient amount of hydraulic oil, but they do reduce the wear losses of most groups. When the dimple diameter was 250 μm, the dimple depth was 5 μm, the area ratio was 6.6%, and the mass loss of the 1040 steel disc was reduced by 90% compared to the smooth reference. In comparison to the behavior of the PTFE-1040 steel tribo-pairs, PEEK-1040 steel friction pairs can provide better tribological performance, whether smooth or dimple-textured. This study offers important insights for the design of seals in machinery. Full article

This study focused on the experiences and perceptions of geriatric healthcare professionals. The research aimed to identify ageism, examine the influencing factors, explore the desired attitudes of geriatric healthcare professionals, and identify institutional changes required for age-integrated efforts and strategies to eliminate these barriers. Interviews with two physicians and eight nurses were conducted in South Korea from August to November 2023, with each session lasting about 1 h, and the transcripts were analyzed using the grounded theory by Strauss and Corbin. The analysis yielded 11 categories, 20 subcategories, and 120 concepts. The central phenomenon was “Ageism that is conducted implicitly and covertly”. Causal conditions affecting the development of ageism were “Difficulties related to the perceived characteristics of older adults” and “Extra burden for older patients and their families”. Contextual conditions were “Provider’s aging anxiety” and “Personal experience about older patients”, and interventional conditions were “Insufficient regular education aimed at ageism prevention” and “Insufficient staffing and resources”. The action/interaction strategies were “Not perceived as a critical issue” and “Perception that it is difficult to change”. After a thorough analysis and materializing of these concepts, the following prevention measures were proposed: “Need for regular education regarding the care of older patients (including ageism) in the nursing educational curriculum” and the “Need for sufficient staffing and resources”. According to the results of this study, medical professionals must satisfy the healthcare needs of the elderly by understanding the proper aging process and tailoring their approach to the specific characteristics of older individuals. To achieve this, organizations should provide adequate resources and personnel. Full article

This paper presents a state-based method to address the verification of $\mathcal{K}$-diagnosability and fault diagnosis of a finite-state vector discrete-event system (Vector DES) with partially observable state outputs due to limited sensors. Vector DES models consist of an arithmetic additive structure in both the state space and state transition function. This work offers a necessary and sufficient condition for verifying the $\mathcal{K}$-diagnosability of a finite-state Vector DES based on state sensor outputs, employing integer linear programming and the mathematical representation of a Vector DES. Predicates are employed to diagnose faults in a Vector DES online. Specifically, we use three different kinds of predicates to divide system state outputs into different subsets, and the fault occurrence in a system is detected by checking a subset of outputs. Online diagnosis is achieved via solving integer linear programming problems. The conclusions obtained in this work are explained by means of several examples. Full article

Understanding the impact of unpredictable environmental fluctuations is crucial in population ecology because such fluctuations are an important feature of natural population systems. In this paper, we consider a stochastic single-species Kolmogorov system under Markovian switching. By using the Lyapunov method, we establish sufficient conditions for stochastic permanence, exponential ergodicity, and extinction of the system. Some examples are presented to illustrate corollaries, showing that our results generalize and improve on some known ones. Full article

In the present article, we create new sufficient conditions for the oscillatory and asymptotic behavior of solutions of third-order nonlinear neutral delay differential equations with several super-linear and sub-linear terms. The results are obtained first by applying the arithmetic–geometric mean inequality along with the linearization method and then using comparison method as well as the integral averaging technique. Finally, we show the importance and novelty of the main results by applying them to special cases of the studied equation. Full article

The present work was carried out as part of the PRIN 2022JCS2CN project “CoolGal”, which aims to design and manufacture a beryllium target cooled by Galinstan (a liquid metal alloy at room temperature) for the production of neutrons using energetic protons. The objective of the present work is to thermo-structurally design a beam window that encloses the environment in which the target is housed. The window consists of a Havar disk, the thickness of which must be minimized to absorb the least amount of proton beam power, while its diameter must be sufficient to avoid excessive beam loss. The window will then be embedded around its perimeter and will have to withstand two load conditions, applied individually: A mechanical load, due to the atmospheric pressure of 0.11 MPa during vacuuming, and a thermal load, due to heating during irradiation with the proton beam. Once a first-version window geometry was defined, a static structural finite element analysis (FEA) was carried out by activating geometric nonlinearities to assess the structural integrity of the window under mechanical loading. After that, a static thermal–mechanical FEA analysis was carried out to assess the structural integrity of the window under thermal loading. Given the compressive stress state induced by thermal loading and the slenderness of the window itself, a nonlinear buckling structural FEA analysis was also performed. Full article

Better understanding mathematical and numerical models often requires investigating the impacts of inputs on the model outputs, as well as interactions. Quantifying such effects for models with non-independent input variables (NIVs) relies on conditional distributions of the outputs given every subset of inputs. In this paper, by firstly providing additional dependency models of NIVs, functional outputs are composed by dependency models (yielding equivalent representations of outputs) to derive distributions of outputs conditional on inputs. We then provide an algorithm for selecting the necessary and sufficient equivalent representations that allow for obtaining all the conditional distributions of outputs given every subset of inputs, and for assessing the main, total, and interaction effects (i.e., indices) of every subset of NIVs. Unbiased estimators of covariances of sensitivity functionals and consistent estimators of such indices are derived by distinguishing the case of the multivariate and/or functional outputs, including dynamic models. Finally, analytical results and numerical results are provided, including an illustration based on a dynamic model. Full article