Claudia Roman, Miguel Ángel Delgado Canto, María García-Pérez
et al.
(1) Background: Developing fully bio-based lubricating greases requires eco-friendly alternatives to conventional harmful components. This study highlights unmodified nanocellulose as an effective structuring agent in vegetable oils, enabling 100% bio-based formulations. (2) Methods: Three bio-based greases were formulated using 1.4 wt.% cellulose nanofibers (CNFs), derived from elm wood pulp through mechanical and chemical pretreatment, as thickening agents in castor oil. Their tribological performance was evaluated under varying temperatures and contact loads and compared to a reference lithium-based grease (LBG) containing 14 wt.% thickener, also formulated with castor oil. (3) Results: Among the CNFs, the unbleached variant (CNF-U) which retained the highest lignin content exhibited the highest coefficient of friction (COF), ranging from 0.09 to 0.14 across test conditions, along with a wear scar diameter of approximately 615 µm at 60 °C. Notable differences in shear stress sensitivity were observed between mechanically and chemically treated nanofibers. The TEMPO-oxidized nanofiber (CNF-TO) grease demonstrated outstanding lubrication stability across contact loads of 10–40 N and temperatures from 25 to 100 °C, maintaining COF values below 0.1—comparable to the reference LBG at 40 N load. Wear scar analysis confirmed that CNF-based greases significantly reduced wear relative to the lithium reference: CNF-B produced the smallest scar diameter (188 µm at 25 °C) while CNF-TO yielded the lowest at 60 °C (457 µm). (4) Conclusions: Nanofiber type and pretreatment significantly impact the tribological performance of CNF-based biogreases. TEMPO-oxidized CNFs provided stable lubrication under varied loads and temperatures, while all CNFs showed strong thermal adaptability, supporting their use in sustainable lubrication.
In this paper, we start with a comprehensive evaluation of the effect of adding differential privacy (DP) to federated learning (FL) approaches, focusing on methodologies employing global (stochastic) gradient descent (SGD/GD), and local SGD/GD techniques. These global and local techniques are commonly referred to as FedSGD/FedGD and FedAvg, respectively. Our analysis reveals that, as far as only one local iteration is performed by each client before transmitting to the parameter server (PS) for FedGD, both FedGD and FedAvg achieve the same accuracy/loss for the same privacy guarantees, despite requiring different perturbation noise power. Furthermore, we propose a novel DP mechanism, which is shown to ensure privacy without compromising performance. In particular, we propose the sharing of a random seed (or a specified sequence of random seeds) among collaborative clients, where each client uses this seed to introduces perturbations to its updates prior to transmission to the PS. Importantly, due to the random seed sharing, clients possess the capability to negate the noise effects and recover their original global model. This mechanism preserves privacy both at a “curious” PS or at external eavesdroppers without compromising the performance of the final model at each client, thus mitigating the risk of inversion attacks aimed at retrieving (partially or fully) the clients’ data. Furthermore, the importance and effect of clipping in the practical implementation of DP mechanisms, in order to upper bound the perturbation noise, is discussed. Moreover, owing to the ability to cancel noise at individual clients, our proposed approach enables the introduction of arbitrarily high perturbation levels, and hence, clipping can be totally avoided, resulting in the same performance of noise-free standard FL approaches.
Telecommunication, Transportation and communications
Pressure and residual chlorine concentration are among the key parameters in urban water distribution networks that require continuous monitoring and control. These networks must ensure that consumer water demands are met with adequate pressure while optimizing water quality parameters, such as residual chlorine concentration, to maximize service satisfaction. In this study, the Najaf Abad urban water distribution network was selected as a real large-scale case study. A simultaneous optimization model was developed to determine nodal average pressure, residual chlorine concentration, and network combined reliability. The multi-objective optimization problem was solved using the NSGA-II algorithm under two extreme water consumption scenarios-maximum and minimum water withdrawal during warm and cold seasons. A Pressure-Driven Analysis approach was employed to calculate network parameters. Additionally, three objective functions were optimized using the NSGA-II multi-objective optimization algorithm. The optimal solution was selected from the Pareto front using the TOPSIS method. The network under study includes four operational pressure-reducing valves; after determining their optimal set pressure values, the average network pressure was reduced by 2.9% during ward days and 13.5% during cold days. The average residual chlorine concentration did not undergo significant changes however, its further reduction was prevented through optimization, effectively achieving this objective as well. Lastly, the combined reliability increased by 1.7% and 1.3% for warm and cold days, respectively.
Technology, Water supply for domestic and industrial purposes
Accurate extraction of polarization resistance is crucial in the application of proton exchange membrane fuel cells. It is generally assumed that the steady-state resistance obtained from the polarization curve model is equivalent to the AC impedance obtained from the electrochemical impedance spectroscopy (EIS) when the frequency approaches zero. However, due to the low-frequency stability and nonlinearity issues of the EIS method, this dynamic process leads to an additional rise in polarization resistance compared to the steady-state method. In this paper, a semi-empirical model and equivalent circuit models are developed to extract the steady-state and dynamic polarization resistances, respectively, while a static internal resistance correction method is proposed to represent the systematic error between the two. With the correction, the root mean square error of the steady-state resistance relative to the dynamic polarization resistance decreases from 26.12% to 7.42%, indicating that the weighted sum of the static internal resistance and the steady-state resistance can better correspond to the dynamic polarization resistance. The correction method can also simplify the EIS procedure by directly generating an estimate of the dynamic polarization resistance in the full current interval.
Mohammad Arani, Mohsen Momenitabar, Tazrin Jahan Priyanka
This research aims to study a real-world example of the unrelated parallel machine scheduling problem (UPMSP), considering job-splitting, inventories, shortage, and resource constraints. Since the nature of the studied optimization problem is NP-hard, we applied a metaheuristic algorithm named Grey Wolf Optimizer (GWO). The novelty of this study is fourfold. First, the model tackles the inventory problem along with the shortage amount to avoid the late fee. Second, due to the popularity of minimizing completion time (Makespan), each job is divided into small parts to be operated on various machines. Third, renewable resources are included to ensure the feasibility of the production process. Fourth, a mixed-integer linear programming formulation and the solution methodology are developed. To feed the metaheuristic algorithm with an initial viable solution, a heuristic algorithm is also fabricated. Also, the discrete version of the GWO algorithm for this specific problem is proposed to obtain the results. Our results confirmed that our proposed discrete GWO algorithm could efficiently solve a real case study in a timely manner. Finally, future research threads are suggested for academic and industrial communities.
In the current recycling process of reclaimed asphalt pavement (RAP), due to the serious damage of aggregate gradation and the large amount of aged asphalt still wrapped around the surface of the treated aggregate, the low recycling rate and poor performance of the recycled asphalt mixture are the major problems of RAP. In view of the shortcomings of RAP recycling technology, it is urgent to research new treatment methods and design specialized asphalt-stripping equipment to solve the existing problems. In this paper, based on theoretical analysis and EDEM discrete element simulation, a principle prototype for efficient micro-damage fine stripping of asphalt on the RAP surface is developed and tested. The results demonstrate that the principle prototype has a satisfactory asphalt-stripping effect and achieves fine stripping of aged asphalt on the surface of aggregate without large-scale crushing. This principle prototype has significant engineering application values, which provides design solutions and data support for further equipment development.
Hans-Martin Heyn, E. Knauss, Amna Pir Muhammad
et al.
Availability of powerful computation and communication technology as well as advances in artificial intelligence enable a new generation of complex, AI-intense systems and applications. Such systems and applications promise exciting improvements on a societal level, yet they also bring with them new challenges for their development. In this paper we argue that significant challenges relate to defining and ensuring behaviour and quality attributes of such systems and applications. We specifically derive four challenge areas from relevant use cases of complex, AI-intense systems and applications related to industry, transportation, and home automation: understanding, determining, and specifying (i) contextual definitions and requirements, (ii) data attributes and requirements, (iii) performance definition and monitoring, and (iv) the impact of human factors on system acceptance and success. Solving these challenges will imply process support that integrates new requirements engineering methods into development approaches for complex, AI-intense systems and applications. We present these challenges in detail and propose a research roadmap.
Abstract Metal organic frameworks contain abundant empty space for selectively absorbing phase change materials (PCM) molecules and sometimes chemically transformed. However, the strong attractive interaction between metal organic frameworks and PCM severely blocks sufficient crystalline-amorphous state transition of PCM. Herein, we proposed an attractive interaction engineering strategy on hierarchical zeolitic imidazolate frameworks (ZIF) based phase change materials (polyethylene glycol/carbon cloth@ZIF, PEG/CC@ZIF) for boosting crystalline-amorphous state transition behavior and electro-/photo- driven thermal performance. Carboxyl-modified CC scaffold regulates attractive interaction between ZIF and PEG, which enhances energy storage capacity of the phase change composite. Moreover, ZIF nanoflakes deposited on the surface of CC reduce the convective heat loss at the solid-gas interface, and CC scaffold facilitates electron transportation and photon penetration, thus significantly enhancing electro- and photo- driven thermal energy storage. Furthermore, ZIF-induced chain effect between PEG and CC enhances the mechanical properties of PEG/CC@ZIF. Notably, commercially available transition metal oxide photocatalyst can be uniformly sprayed on the surface of PEG/CC@ZIF through coordination chemical engineering for multi-functional phase change composite.
The possibility of engineering well‐defined pores into liquid materials is fascinating from both a conceptual and an applications point of view. Although the concept of porous liquids was proposed in 2007, these materials had remained hypothetical due to the technical challenges associated with their synthesis. Over the past five years, however, reports of the successful construction of porous liquids based on existing porous scaffolds, such as coordination cages, organic cages, metal–organic frameworks, porous carbons, zeolites, and porous polymers, have started to emerge. Here, the focus is on these early reports of porous liquids as prototypes in the field, classified according to the previously defined types of porous liquids. Particular attention will be paid to design strategies and structure–property relationships. Porous liquids have already exhibited promising applications in gas storage, transportation, and chemical separations. Thus, they show great potential for use in the chemical industry. The challenges of preparation, scale‐up, volatility, thermal and chemical stability, and competition with porous solids will also be discussed.
This paper presents a constrained connected automated vehicles (CAVs) trajectory optimization method on curved roads with infrastructure assistance. Specifically, this paper systematically formulates trajectory optimization problems in a spatial domain and a curvilinear coordinate. As an alternative of temporal domain and Cartesian coordinate formulation, our formulation provides the constrained trajectory optimization flexibility to describe complex road geometries, traffic regulations, and road obstacles, which are usually spatially varying rather than temporal varying, with assistances vehicle to infrastructure (V2I) communication. Based on the formulation, we first conducted a mathematical proof on the controllability of our system, to show that our system can be controlled in the spatial domain and curvilinear coordinate. Further, a multiobjective model predictive control (MPC) approach is designed to optimize the trajectories in a rolling horizon fashion and satisfy the collision avoidances, traffic regulations, and vehicle kinematics constraints simultaneously. To verify the control efficiency of our method, multiscenario numerical simulations are conducted. Suggested by the results, our proposed method can provide smooth vehicular trajectories, avoid road obstacles, and simultaneously follow traffic regulations in different scenarios. Moreover, our method is robust to the spatial change of road geometries and other potential disturbances by the road curvature, work zone, and speed limit change.
Transportation engineering, Transportation and communications
Rainfall is the main factor leading to the landslide of expansive soil slope. To deeply understand the instability mechanism of expansive soil slope under rainfall conditions, it is necessary to clarify the strength attenuation mechanism of expansive soil caused by water absorption and swelling. Therefore, the improved constant volume direct shear test was used in this study to compare with the conventional test, focusing on the variation of effective shear strength parameters with dry density (volume). The micromechanism of expansive soil strength attenuation is further studied, and the influence of expansive soil on slope stability is analyzed by numerical calculation. The results show that the improved direct shear apparatus and method can keep the volume of expansive soil specimens unchanged before and after shear and obtain the real effective shear strength parameter of soil. Under the same conditions, the shear strength parameter of the improved direct shear test is lower than that of the conventional direct shear test. The rapid thickening of the lamellar structure of montmorillonite in expansive soil will lead to the fragmentation and dispersion of clay particles, which is one of the fundamental reasons for the strength difference between expansive soil and ordinary clay. In slope stability analysis, the effect of swelling on the shear strength of slope cannot be ignored and should be considered in engineering design.
YU Jin 1, YAO Wei 1, REN Wen-bing 2, FAN Zhi-zhong 3, QIN Wei 4
In order to explore its deformation and failure laws under cyclic disturbance, a series of uniaxial tests of marble with different stress levels and cyclic amplitudes are carried out. The research results show that: (1) The stress level is the decisive factor whether the marble specimens tend to failure or not, and the cyclic amplitude is a relatively minor factor. When the stress level just reaches the dilation one, the rock specimen can not fail even if it is under a much larger cyclic amplitude. When the stress level is much higher than the dilation stress and the cyclic amplitude is given a much larger value, the rock will rapidly fail. (2) Compared with the irreversible deformation, the dynamic stiffness can better reflect the transition features of sparse-dense-sparse stages. The positive and negative values of decay rate of the dynamic stiffness can be used as the features of failure precursor, and the rock failure can be predicted at the stable deformation stage. (3) For the failed marble specimens, the damage variable based on the dynamic stiffness characterization is similar to the general trend of irreversible deformation. The double-high mode is consistent with the type Ⅰ curve, and the rest of the curves are consistent with the type Ⅱ curve.
Engineering geology. Rock mechanics. Soil mechanics. Underground construction
Bikeshare offers a flexible feeder mode to metro and improves the overall connectivity of urban public transport systems. Although bikeshare has received much research attention, the relationship between the built environment and bikeshare-metro integrated use (i.e. the use of bikeshare for the first/last mile) remains underexplored. Using a one-month dataset of bikeshare trip records in Nanjing, China, this research scrutinizes the built environment correlates of the integrated use. A generalized additive mixed model is employed to capture the temporal autocorrelation attributable to repeated observations over time and the spatial autocorrelation resulting from geographical proximity between individual metro stations. The results show that built environment variables do impose salient nonlinear effects on the bikeshare-metro integrated use. For example, population density only increases the integrated use at certain intervals, and interestingly, extremely high density leads to a decline in bikeshare-metro integrated use. The proportion of commercial and greenspace land uses within metro station catchment areas should not be too high or too low. There exists an optimal land use setting that maximizes the utility of land-use interventions. These findings provide useful policy implications for developing an environment that facilitates the integration of bikeshare and urban metro systems.
Using two different methods, a previously developed elliptic blending model (the original <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi><mtext>-</mtext><mi>φ</mi><mtext>-</mtext><mi>α</mi></mrow></semantics></math></inline-formula> model) is modified for sensitization to streamline curvature. One method involves modifying the dissipation term in the turbulent dissipation equation, while the other constructs a new formulation for the turbulent kinetic energy production term based on an explicit algebraic stress model. The capabilities of the proposed models are evaluated by applying them to three flows with curved surfaces; namely, the two-dimensional (2D) infinite serpentine passage flow, the 2D U-turn duct flow, and the 2D periodic hill flow. The <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi></mrow></semantics></math></inline-formula> model with rotation and curvature correction (the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi><mtext>-</mtext><mi>C</mi><mi>C</mi></mrow></semantics></math></inline-formula> model) is also used for comparison. The computed results are compared with the relevant direct numerical simulation, experimental, and large eddy simulation data from the literature. It is found that the two proposed models significantly improve upon the original <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi><mtext>-</mtext><mi>φ</mi><mtext>-</mtext><mi>α</mi></mrow></semantics></math></inline-formula> model. Compared with the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi><mtext>-</mtext><mi>C</mi><mi>C</mi></mrow></semantics></math></inline-formula> model, the two proposed models produce better results in the 2D infinite serpentine passage flow and the 2D periodic hill flow. The proposed models are similarly competitive with the <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>STT</mi><mrow><mo> </mo><mi>k</mi><mtext>-</mtext></mrow><mi>ω</mi><mtext>-</mtext><mi>C</mi><mi>C</mi></mrow></semantics></math></inline-formula> model in the 2D U-turn duct flow.