Background/Objective: In recent years, treatment of heart failure patients has proved to benefit from implantation of pressure sensors in the pulmonary artery (PA). While longitudinal measurement of PA pressure profoundly improves a clinician’s ability to manage HF, the full potential of central venous pressure as a clinical tool has yet to be unlocked. Central venous pressure serves as a surrogate for the right atrial pressure, and thus could potentially predict a wider range of heart failure conditions. However, it is unclear if current sensor anchoring methods, designed for the PA, are suitable to hold pressure sensors safely in the inferior vena cava. The purpose of this study was to design an anchoring system for accurate apposition in inferior vena cava and evaluate whether it is a potential site for central venous pressure measurement. Materials and Methods: A location inferior to the renal veins was selected as an optimal site based on a CT scan analysis. Three anchor designs, a 10-strut anchor, and 5-struts with and without loops, were tested on a custom-made silicone bench model of Vena Cava targeting the infra-renal vena cava. The model was connected to a pulsatile pump system and a heated water bath that constituted an in-vitro simulation unit. Delivery of the inferior vena cava implant was accomplished using a preloaded introducer and a dilator as a push rod to deploy the device at the target area. The anchors were subjected to manual compression tests to evaluate their stability against dislodgement. Computational Fluid Dynamics (CFD) analysis was completed to characterize blood flow in the anchor’s environment using pressure-based transient solver. Any potential recirculation zones or disturbances in the blood flow caused by the struts were identified. Results: We demonstrated successful anchorage and deployment of the 10-strut anchor in the Vena Cava bench model. The 10-strut anchor remained stable during several compression attempts as compared with the other two 5-strut anchor designs. The 10-strut design provided the maximum number of contact points with the vessel in a circular layout and was less susceptible to movement or dislodgement during compression tests. Furthermore, the CFD simulation provided haemodynamic analysis of the optimum 10-strut anchor design. Conclusions: This study successfully demonstrated the design and deployment of an inferior vena cava anchoring system in a bench test model. The 10-strut anchor is an optimal design as compared with the two other 5-strut designs; however, substantial in-vivo experiments are required to validate the safety and accuracy of such implants. The CFD simulation enabled better understanding of the haemodynamic parameters and any disturbances in the blood flow due to the presence of the anchor. The ability to place a sensor technology in the vena cava could provide a simple and minimally invasive approach for heart failure patients. Heart Failure (HF) affects an estimated population of 26 million people worldwide. It is associated with significant hospitalization in the United States and Europe, with over 1 million admissions per year reported in both the countries . Within With the incidence of HF on the rise, the notion of designing and developing a simple, valid, and reliable system to monitor symptoms or progression of HF is widely acknowledged ,7,8. TheCVP and its surrogate right atrial pressure (RAP) could provide essential diagnostic information for the treatment of pathologies as diverse as right-sided and left-sided heart failure, chronic kidney disease, acute kidney injury, pulmonary hypertension, liver disease, and most importantly, systemic congestion . An incrControlling congestion is the key challenge to heart failure management, which helps stabilize symptoms and sudden health deterioration eventually resulting in death . ClinicaCentral venous catheterization remains the gold standard for CVP measurement. Although regarded as the most accurate and effective method, it is a time consuming invasive procedure, and associated with potential complications involving infections, catheter-induced thrombosis, and arterial puncture ,22,23,24An alternative method to estimate CVP is through assessment of peripheral venous pressure (PVP) by transducing a peripheral intravenous line. Such studies have yielded mixed results. Correlations between PVP and CVP need to be studied specifically in a heart failure population ,26.Another non-invasive technique is the near-infrared spectroscopy used to detect jugular venous pressure (JVP) in the neck. This system uses a single wavelength LED and photodetector to measure JVP, and requires the patient to lie down at an angle where the JVP pulse aligns with the infrared sensor. Although this method yields similar results to those measured invasively, it is not used routinely in a clinical setting .A study by Marcelli et al. introduced a non-invasive device for CVP assessment designed for use in hospitals, offices, and home. This device operates on the principle of venous occlusive plethysmography, extensively used for other applications in a clinical setting. Limitations of this technique requires the patients to be mobilized with the cuffs connected to a graphical user interface system . MoreoveCVP measurements targeting inferior vena cava (IVC) as a potential site of interest remains unexplored.Current sensor anchoring methods, which are effective for other arteries e.g., pulmonary artery, may fail to hold the sensor safely in place in the physically more challenging environment of the IVC .Significant physical and functional adaptation of existing haemodynamic sensors is required for a safe and effective implant in the IVC.Currently, to the author’s knowledge, there is limited research focusing on implantable or wireless monitoring techniques for continuous real-time measurements of CVP. This study aimed to address the following unmet needs:Haemodynamic IVC monitoring presents a challenge arising from the physiology of IVC. IVC is relatively a compliant vessel as compared with others and is prone to easy distortion due to forces applied by implants. This may adversely affect the performance and the precise monitoring capability of IVC implants. There is a requirement of a reliable and affordable wireless monitoring system, particularly in the field of heart failure monitoring. A unique challenge for implants in the IVC is its asymmetrical shape and dynamics during collapse and expansion. IVC tends to collapse in the anterior–posterior direction, moving from a circular shape to a flat, oval cross-section, resulting in a change in blood volumes . An implDesign and optimization of an anchoring system in the IVC for a safe long-term implant with minimal or no-risk is an unmet clinical need. Some studies have emphasized the anchoring mechanism of vena cava filters and stents, indicating the requirement for additional post-implant procedures to secure the stent or filter from migrating to the right heart. More than 71% of patients with intravascular foreign bodies experience major complications such as cardiac arrhythmias, sepsis, and cardiac tamponade . Post-imRecommendations to improve anchoring include oversizing by selecting a stent diameter greater than the diameter of the vein, interlocking stent techniques and pull-through wire system that would facilitate a safe and precise placement of the device ,37. PhysOver the last few decades, two types of implanted devices have targeted the IVC; the vena cava filters and venous stents. IVC filters have gained popularity to prevent acute pulmonary embolism (PE) in patients with deep vein thrombosis (DVT). Although the vena cava filters proved to have a significant benefit on mortality in unstable patients , severalVenous stents are gaining popularity in the field of interventional medicine and serve as a new treatment paradigm for patients with chronic venous obstruction. Some major technical limitations related to the design of Wallstents  have been reported. The first shortcoming is the weaker edge of stent that is prone to occlusion or collapse when placed in a diseased or compressed iliac vein . UnsucceLearnings from previous implants (filters and stents) in IVC highlight the requirement of a safe anchoring system that would overcome limitations such as IVC penetration, embolization, occlusion, and device migration.In this study, we introduced a novel anchoring system compatible with existing sensor technology in the IVC for the purpose of non-invasive CVP measurement. We tested the feasibility and ease of implantation of the novel anchor in a suitable bench test model. Investigation of the haemodynamic parameters of the anchor was performed using CFD analysis, simulating blood flow inside a 3D IVC model with the anchor.This section details the design implementation of the anchor on the bench and its numerical analysis using CFD. The process flow  providesIVC is considered as an optimal site for implantation since it presents a straight tube and provides a relatively easy access point when compared with the superior veins . AccordiA novel anchor was designed to accommodate the specific constraints of the target site in the IVC. The design of this anchor is based on pre-existing arterial stents but simplified to a single thread of ten struts arranged cylindrically.The nitinol anchor wires  have an austenite final temperature below room and body temperatures. This results in anchor wires maintaining their super-elastic properties under normal use cases and not utilizing the temperature-dependent shape memory return to perform their intended function, which is common to other nitinol wire applications.TM BF51828C1, Waltham, MA, USA). The dwell time range to shape set anchors was set to 16 min, 15 s ± 10 s. The moulds were quenched in a water bath (35 °C) for 30 s. Anchors were visually inspected to ensure the desired shape was set in the wire.The straight nitinol wires were shape set using suitable fixtures or moulds . This mold allows anchor struts to be arranged cylindrically with termination points facing away from the cylindrical mould that allows attachment to the sensor body. The anchor wires with the fixture were subjected to heat treatment at 550 °C in a box furnace  and prevent the risk of dislodgement post deployment b.5-strut anchor design without loops c.Three candidate anchor designs were fabricated that vary in the number of struts and the presence of loops:Dummy glass sensor bodies (20 mm × 4 mm × 2 mm) were used for the purpose of bench deployments to evaluate anchorage and deployment accuracy. Attachment of the anchor to the dummy sensor body was established using nylon sutures. The termination points of the anchor constitutes a loop  intendedThe bench test model is a silicone model of the Vena Cava  vasculature with superior and inferior veins, right heart, and coronary sinus.To evaluate the deployment of the novel anchor design in the IVC, a bench top stand was set up which included a 3D printed model of the relevant anatomy connected to a pulsatile pump system  a. The deA set of Introducers  ranging from 14 Fr–22 Fr were used to test suitability for loading and deploying the IVC anchors on the bench model. Various combinations of introducers and anchors were tested on the bench to guide selection of an optimal delivery system. The anchors were crimped and loaded at the tip of the introducer using an appropriate size Falcon tube. The objective for testing various range of introducers is to check the possibility of any kinks during anchor loading, any oversized introducer-anchor combinations, and to assess the ability of the anchor to move effortlessly within the introducer following manual push force from the dilator ensuring appropriate deployment.The implantation concept is illustrated in The opening or access site in the model is the right iliac vein secured with a haemostatic valve. The introducer and dilator were advanced through this valve to achieve implantation at the target location. The device was deployed by pushing the dilator rod through the introducer sheath to release the anchor with sensor body attached. After deployment, anchorage at the target location was inspected visually in the anatomical model. In the next step, collapse of the vessel was induced using external physical force or pinching of the model at the location of the device. The model was disturbed and compressed from all angles and along the length of the device. These compression and stress tests were performed to analyze deployment orientation and potential for device dislodgement.Fifteen anchor deployments in total (five attempts per design) were executed on the bench. Accuracy of deployment and anchorage within the vessel were assessed for all the anchor designs. Manual compression tests were performed post deployment on each of the anchor designs to assess the risk of dislodgement, and evaluate if the designs could withstand vein collapsibility or dynamic force exerted on them. This has a potential clinical significance in heart failure/hypervolemic patients with a vena cava collapse of ≤50 percent . It is iThe criteria for successful deployment were determined as if the device was deployed at the desired location in the correct position with the anchor struts secured against the vessel wall and if the sensor body was in the desired position. Successful anchorage was determined if the sensor body and anchor remained in the position after several compression tests.Following bench test simulations, a CAD profile of the selected 10-stut anchor design a and theCFD analysis of a control model and an assembled anchor and IVC model was completed using ANSYS Fluent software (ANSYS 2022 R1). The control model refers to the IVC without anchor. The geometry was first meshed using structured hexahedral elements for both the anchor and the IVC. A grid size of 1.2 mm was selected. Local refinement was completed to maintain adequate mesh resolution. A mesh convergence study was completed, and 501,000 elements were used for model.The length of the IVC and iliac veins were extended to 300 mm to allow enough length for blood flow to develop and for the results to be independent of the vein lengths. Velocity inlet boundary condition was imposed at the right and left iliac vein and pressure outlet at the IVC, labelled in The pressure outlet was set as 0-gauge pressure. No-slip boundary conditions were applied to the walls of the geometry. The flow for the simulation was considered transient and incompressible. The calculated maximum Reynolds Number and Womersley Number in the IVC were 1500 and 9.6, respectively. This suggests that the blood in the IVC can be characterized as laminar and plug flow.Blood can be modeled as Newtonian or non-Newtonian fluid . ViscousThe relationship between non-Newtonian blood dynamic viscosity equation ,51, demo3.The following constants defined by Boyd et al.  were use−1 [Blood flow through the anchor disturbs flow causing flow separation, resulting in blood tapering inwards distal to the anchor. This induces changes in the wall shear stress (WSS) in the anchor region, which can be evaluated through time averaged wall shear stress (TAWSS), oscillatory shear index (OSI) and relative residence time (RRT). These haemodynamic parameters are indicators of blood stagnation leading to blood clotting or thrombosis. If the haemodynamic parameters are above the critical ranges, the endothelial cells of the IVC adopt an atherosclerotic profile. The critical range is as follows: TAWSS < 0.4 Pa, OSI > 0.3 and RRT > 10 Pa−1 .WSS is a vector quantity. TAWSS measures the magnitude component of the vector quantity. Low TAWSS values are indicators of low blood velocities. OSI quantifies the directional component of the vector quantity. It ranges between 0 (no change in direction of blood flow) and 0.5 . High OSI suggests that the blood is in oscillating state with a higher risk of blood clotting due to formation of secondary flow zones. High RRT reflects the residence time of blood particles stagnant at one location, as compared with blood particles in other locations of the IVC.T is the time period for one cardiac cycle. WSS and t are the instantaneous wall shear stress and time stamp of the cardiac cycle.Equations (2)–(4) were used to calculate the haemodynamic parameters. Here, TAWSSOSIRRTWSS magnitude and x, y, and z values were exported from ANSYS and post-processed in MATLAB (R2021B) to calculate TAWSS, OSI and RRT.The 10-strut and 5-strut anchors were subjected to manual compression tests, which simulate the vena cava collapse during an inspiration-expiration cycle. The compression tests were divided in three categories that simulated a 25%, 50%, and 100% collapse. This means that the IVC was compressed manually at 100% (full collapse), 50% , and 25% (one-fourth collapse).Five compression attempts in each category  resulted in anchor dislodgements, and these were represented as anchor type versus the number of times each anchor collapsed at 25%, 50%, and 100% . The 10-The 5-strut versions are not suitable to withstand the vena cava collapsibility and possess a higher risk of migrating to a zone of larger diameter and/or blocking renal or other veins in proximity. The 10-strut anchor has the ability to resist migrating forces simulated by manual compression. Additionally, the more the contact points with the vessel, the more stable the design.The control (IVC without anchor) model was compared to the anchor model in CFD, which allowed analyzing the differences in fluid behavior due to the anchor.Blood flow profiles were analyzed at time points t1 and t2  during t1) as compared with diastole (t2). Flow separation can be seen at the bifurcation point. However, this does not affect blood flow in the anchor as the anchor is placed further into the IVC.The results showed that blood velocity is much higher during systole  were computed using MATLAB, as shown in High OSI values are seen at the edges of the strut in This study presented the first steps in designing anchors for an active sensing implant suitable for the inferior vena cava for central venous pressure measurement. The anchors designed were feasible to implant in a silicone vasculature of vena cava  and provided good anchorage at the target site. The 10-strut anchor design is more stable than the two other 5-strut designs. Although all anchor designs passed the basic feasibility tests on the bench, only the 10-strut anchor could withstand migration forces induced by manual compression attempts that simulated vena cava collapse. The methods applied to evaluate the anchor designs allowed identifying challenges in relation to the mode of deployment depending on the complexity and size of the anchor and selection of an optimal size delivery system. The double-introducer push-rod concept proved to be an effective delivery system to deploy the redefined anchors. The 14 Fr size  was a good fit to load the implant, while an 18 Fr size  was ideal for use as an outer introducer to guide to the target location.The results from CFD analysis provided an understanding of the blood flow through the length of the anchor. Comparison between the control and anchor model allowed identifying any changes in blood flow due to the presence of the anchor. The Reynolds and Womersley values calculated suggested that the blood flow in the IVC is in the laminar regime and adopts a plug flow profile. There was no significant change in the blood flow due to the presence of the anchor. The edge of the anchor caused some flow separation, which led to the flow stream distal to the anchor to detach slightly from the IVC walls. This ‘tapering’ effect of blood stream occurred up to 40 mm distal to the anchor end. After this, the blood resumed a plug flow profile as any disturbances in blood due to flow separation ceases. A small increase in the percentage surface area of the anchor in the critical range was observed. This is expected as the edge of the anchor causes a disturbance in the blood flow. The critical range refers to a zone of low blood velocity and higher OSI, WSS, and RRT. The percentage surface area of the anchor in the critical range was minimum and less significant. Clinically, this would mean that future patients could be associated with a low risk of blood clotting, blood stagnation, or recirculation zones from IVC implants.According to physicians, the implant procedure in IVC should take no more than fifteen minutes. Nonetheless, there is a high risk of device migration in the IVC as evident from the lessons learnt from IVC filters. Other complications include IVC occlusion, vessel penetration, filter embolization, and access site thrombus. Moreover, the pelvic movements also have an influence on the implants in the IVC region that contribute to device migration or dislodgement ,40,41,42TM implant [Haemodynamic sensors in the IVC combined with a safe anchoring system could help in establishing long-term continuous central venous pressure waveforms. Current sensor technologies such as CardioMEMS  (Abbott) implant   focus on maintaining a balance between flexibility and radial force. Flexibility enables the stent to conform to the shape of the vein without kinking because of pelvic movements and decreasing the cross-sectional area . Stents The 10-strut anchor is an optimal design and feasible for implantation in-vitro, however it needs to undergo a series of ORF, strength and fatigue tests to validate safety and efficacy of implantation in-vivo. A second limitation is the addition of hooks or barbs to the anchor design to improve the ORF and prevent risk of dislodgment to a zone of larger diameter. The addition of hooks demands for a more complex design of the anchor and involves a higher risk of penetrating the IVC wall over a certain period. Therefore, it requires several attempts to develop the ideal structure for a venous implant that would afford the best balance between the said design parameters.The deployment mechanism using the introducer system can sometimes cause the anchor to spring radially within the IVC. This can result in anchor deployments slightly away  from the target location. To mitigate the risks involved with this deployment technique, we placed the introducer loaded with the anchor slightly above the iliac bifurcation and a few inches below the target location to achieve the desired orientation and deployment. The sensor body is facing laterally within the introducer so that the radial spring force results in a deployment with sensor body attached to the anterior wall of vessel. This could also help to prevent any tilts during anchor deployment.The orientation of the sensor body can affect the measurements. If the sensor is located at the posterior wall of the vessel, the link distance (distance between the implant and the skin surface) increases and the accuracy of the measurements is compromised. The deployment technique employed in this study helped to identify challenges with orientation or positioning of the sensor within the IVC, required hand-push force to deploy the anchor, and its effects (tilts or migration) on the deployment accuracy.The CFD simulation assumes that the IVC walls are rigid. A rigid wall model could overestimate wall shear stress and thus the haemodynamic parameters. This suggests that the estimated values might be an over prediction. Fluid Structure Interaction (FSI) modeling can be completed to incorporate changes in blood flow through the anchor due to the elasticity of the IVC walls. Further analysis of performance of the anchor should include patient specific IVC models to create realistic 3D anatomical maps of various IVC morphologies. This would provide an insight into designing more flexible, tortuous designs, accommodating irregularities in the IVC.This study successfully demonstrated the design and deployment of an IVC anchor system in a bench test model. The bench test simulation provided useful insights into the design and fabrication, selection, and analysis of the anchor, while the CFD simulation provided an understanding of the haemodynamic changes around the anchor zone, as well as risk factors anticipated post implantation. However, substantial in-vivo experiments are required to validate the safety and accuracy of the IVC implant. The clinical value of this research focuses on an improved assessment of the potential value of CVP measurements in predicting and managing congestive heart failure that will drive specific diagnoses and treatment modalities. The ability to place a sensor technology in the vena cava could provide a simple and minimally invasive approach for HF patients.


During the construction of rail transit, some road resources are occupied under construction and hence the capacity of affected road sections is reduced. Due to such temporary impact, the low operational efficiency of bus routes when passing these road sections is following suit, which is inevitably detrimental to the short-term traffic conditions and the urban environment. This paper proposes a three-step adjustment framework to actively mitigate the impact of rail transit construction on bus operations. In Step I, a criterion is developed for selecting bus routes significantly affected due to rail transit construction. In Step II, we design a stop-skipping strategy and truncation strategy, and check whether they are opportune to ameliorate the service of each affected bus route. Yet, these two strategies result in a loss of ridership since some previous stops are not served. In Step III, the feeder bus service is further designed to guarantee spatial coverage nearby the construction area. A mixed-integer linear programming model is developed to determine the optimal configuration of the feeder bus service incorporating two strategies. Finally, a case study based on the Sioux-Falls network is carried out to demonstrate that the proposed adjustment framework is conducive to mitigating negative construction effects and reducing costs. In the process of continuous urbanization, the urban population and associated travel demand keep growing. Many metropolitan areas attempt to extend their service coverage of public transit by constructing new rail transit lines to accommodate the increasing travel demand3. Rail transit lines are generally built along transportation corridors with high passenger flow. The passenger flow of these corridors is previously serviced by bus transit.Targeting the sustainable development of urban transport systems, public transit is commonly regarded as an effective way to alleviate traffic congestion, reduce emissions, and address other environmental issues resulting from transportationDuring the construction of rail transit, the capacity of road sections under construction is reduced. The construction period of rail transit is long, which inevitably affects the operational efficiency and level of service of related bus routes. Some passengers who originally took buses may choose other modes of transport, such as private cars. This is not conducive to mitigating traffic congestion and the sustainable development of the city. Thus, some active adjustment measures need to be taken to improve the inefficient bus operations resulting from rail transit construction.7. Few studies pay attention to the impact on bus transit during the construction of rail transit. After the completion of rail transit, the purpose of bus route adjustment is to reduce duplication with rail transit lines and well couple with rail transit in service. While during the construction of rail transit, bus routes adjacent to the construction area may be influenced. These bus routes should meet basic demand and meantime maintain certain service quality via reducing the impact of construction on bus operations. Hence, an adjustment framework for mitigating the impact of rail transit construction on bus operations is necessary, which is addressed in this paper.The bulk of the current literature focuses on the issue of coordination between rail transit and buses after the completion of rail transit8. Bi-level programming model was also proposed to optimize the adjustment schemes of bus routes, taking the impacts of the urban rail transit network into account to minimize the passenger travel cost and maximize the benefits of bus operators5. The reconfiguration of bus services in an urban area with a newly constructed rail transit system was investigated; the rail transit services are taken as the backbone, and the bus services are reconfigured to better integrate with rail services9. Recently, Cui et al. proposed a model for the adjustment of bus routes along a rail transit line; the generalized travel time costs and travel time savings proportion in the collinear section of rail transit and bus was optimized6. Wei et al. studied how to adjust and optimize the original bus routes based on bus and metro integration7.After the completion of rail transit, the bus routes should be adjusted to coordinate with the in-use rail transit lines. Many researchers have made efforts to the coordination problem between bus and rail transit. A multi-objective model was developed for designing an integrated rail transit and bus network on a transit corridor with a new rail transit route10. Several studies have been conducted to analyze the impact of work zones on ground transportation. The optimization of project schedule and traffic flow organization was investigated to reduce traffic delay and travel costs resulting from the disturbance of work zones13. Concerning the impact of rail construction on bus routes, Huang et al. proposed a method to evaluate the performances before and after the adjustment of the bus routes14.During rail construction or road maintenance, several work zones are formed, which occupy the road resource and influence the operation of ground transportation15. Verma et al. discussed a model for developing optimal feeder bus routes, within an integrated mass transit planning framework, for urban rail transit stations16. Xiong et al. constructed a route design model for feeder buses to minimize the total cost and obtained the optimal stations using heuristics algorithms17. Lin and Wong presented a feeder bus route design model, to minimize route length and travel time and maximize service coverage; a multi-objective programming approach was developed to solve the model18. The optimized results dominate the existing bus routes in terms of all objectives and stakeholder concerns, except for the risk of trip generation estimation that bus service providers are mostly concerned with. Zheng et al. proposed a nonlinear mixed-integer programming model to address multiple circular feeder bus route design problems19. It found that in areas with a mature public transport system, combining adjusting existing bus routes and designing new feeder routes together is a more cost-effective way. Recently, Cao et al. studied a feeder bus route optimization problem to minimize the sum of bus operation cost and passenger travel cost20. The results show that compared with the existing transit network, the optimal scheme improved the passenger-carrying rate, reducing the per capita travel cost and improving the overall operating efficiency. These studies have reported many positive findings on the operations of feeder buses for in-use transit systems. However, the role of feeder buses during the construction period of rail transit has not been studied particularly.As an important complement, the feeder bus service effectively extends the service scope of rail transit and solves the problem of short-distance travel24. Under the stop-skipping service pattern, bus trips skip some of the stops of the original bus route25. Except for designing stop-skipping routes in tactical planning, the stop-skipping strategy can also be used for real-time and emergency bus management. Zhang et al. developed a real-time agent-based simulation model to optimize the dynamic bus stop-skipping and holding schemes26. The objective was to reduce passenger waiting and on-board time and improve the reliability of bus service. Zhao et al. used a stop-skipping method for bus fleet scheduling to meet sudden increases in demand27. The stop-skipping decision and fleet size are modeled as a dynamic program to obtain the optimal strategy that minimizes the passenger waiting time. The proposed approach reduced the total waiting time for passengers by more than 20%.The stop-skipping strategy has been studied by many researchers to increase bus operating speedsIn conclusion, the impact of rail transit construction on bus operations and the adjustment of bus services from the network level have not been studied particularly, though some existing studies provide a reference for the bus operations during the rail construction. In addition, to the best of our knowledge, there is no research on the application of feeder bus service to the bus adjustment during the construction period of rail transit.The primary objective of this study is to propose an adjustment framework in an effort to actively mitigate the impact of rail transit construction on bus operations. For bus routes that need to be adjusted, we first check whether the stop-skipping and truncation strategies are effective in reducing the total cost. Bus routes where these two strategies are invalid are optimized through the design of the feeder bus route. A mixed-integer linear programming model (MILP) is developed to determine the optimal configuration of the feeder bus service. To sum up, the contributions of this paper are threefold: (1) A three-step adjustment framework is proposed to actively mitigate the impact of rail transit construction on bus operations. (2) We propose a quantitative indicator to determine whether the stop-skipping and truncating strategies are effective. (3) The feeder bus route is designed to optimize the bus routes affected by the construction of rail transit. Affected bus routes bypassing the construction sections directly would affect the ride of some passengers, the feeder bus service can address this issue. The proposed adjustment framework could reduce total system cost and relieve the impact of rail transit construction on passengers, which is conducive to mitigating traffic congestion and enhancing the sustainable development of the city.The remainder of this paper is organized as follows: In “Consider a rail transit line under construction in the urban transportation network. Some road resources are occupied during the construction and hence the capacity of affected road sections is reduced. As a result, the low operational efficiency and poor service level of related bus routes when passing these road sections are following suit. Let For ease of presentation, the notations for parameters and variables used in this paper are summarized in Table A three-step adjustment framework is proposed to actively mitigate the impact of rail transit construction on bus operations and its flowchart is shown in Fig. Each bus route is affected by construction to a different degree. In Step I, an indicator is first proposed to evaluate whether the bus route is significantly affected due to rail transit construction and needs to be adjusted. The set of bus routes that need to be adjusted is denoted by In Step II, we design two strategies, i.e., the stop-skipping strategy and truncation strategy, and check whether they are opportune to ameliorate the service of each bus route in entclass1pt{minimaentclass1pt{minimaentclass1pt{minimaThese two strategies may reduce operating costs, as well as some passengers’ travel costs because they experience a shorter travel time. Yet, the two strategies may result in a loss of ridership since some stops are not served. Passengers who start or end at these stops will not be able to ride. Assume the penalty for losing one passenger is 28. Besides, bus travel speed (which can be reflected in travel time) is a fundamental indicator for the bus service evaluation29. Therefore, we choose the increasing rate of roundtrip time as the indicator for selecting bus routes which are significantly affected due to rail transit construction and necessitate being adjusted. The increasing rate of roundtrip time of bus route As the rail transit is under construction, the affected bus routes need to serve their original passenger flow and cannot bypass the construction section directly. Whether an affected bus route needs to be adjusted is based on the impact degree of construction on the bus route. Travel time is found to be one of the most important factors in travel choicesThe set of bus routes that satisfy Route cost is defined as the sum of the operating cost and passenger travel cost of a bus route. For any bus route, if the stop-skipping strategy can reduce the route cost, then the stop-skipping strategy is adopted. Hereinafter, all the costs calculated refer to the hourly costs. Assume the construction only affects link travel time and does not affect dwell time at bus stops. The total travel time of passengers on bus route 23:It is assumed that dwell time only depends on the number of boarding and alighting passengers, and the effects of other factors are ignored. The bus vehicles in most cities have two doors, one for boarding and one for alighting, thus at each stop, the dwell time is equal to the maximum value between boarding time and alight timeThe total operating cost of bus route With the stop-skipping strategy, the total travel time of passengers on bus route With the stop-skipping strategy, the total operating cost of bus route The passenger loss caused by the stop-skipping strategy is:The criterion for implementing the stop-skipping strategy The truncation strategy refers to skipping the bus stops not only in the affected section but also in the upstream section (or the downstream section), that is, the entire bus route only retains the downstream section (or the upstream section). For any bus route, if the truncation strategy can reduce the route cost, then the truncation strategy is adopted. Notice that if a bus route meets the criteria of both the stop-skipping and the truncation strategies at the same time, then the truncation strategy is adopted.The total travel time of passengers and the total operating cost of bus route entclass1pt{minimaWith the truncation strategy, the total operating cost of bus route The passenger loss caused by the truncation strategy is:The criterion for implementing the stop-skipping strategy The two terms on the left-hand side of inequation  represenThe aforementioned two strategies may result in the reduction of service coverage since some previous stops are not served. In Step III, the feeder bus service is designed to guarantee spatial coverage nearby the construction area on the one hand. On the other hand, for bus routes Let The starting and terminal stops of the feeder bus service are the first and last stops in set where decision variables Equation  defines straints –28) def def\docustraints  ensures straints  and 31)\documentstraints  ensures straints  ensures straints –35) ens ens\docustraints  depicts straints  ensures nstraint  defines The model defined by Eqs. –38) inc inc38) iTo demonstrate the effectiveness of the proposed adjustment framework, a case study is conducted in this section. A hypothetical transit network based on the Sioux-Falls network Fig.  is used According to Eq. , the inc on Eqs.  and 22)\documentThe values of Feeder bus service is designed to optimize bus routes 3, 4, 5, and 6. The starting and terminal stops of the feeder bus are stops 5 and 21, respectively. The set of affected stops of the four bus routes is given by An evaluation of the proposed approach is employed by calculating the total cost before and after the route adjustment scheme. The variation in the number of passengers and route costs with the route adjustment scheme is shown in Table To evaluate the impact of the adjustment scheme on traffic congestion, we define bus vehicle time To analyze the impact of increased link travel time caused by rail construction on the route adjustment scheme, an increasing proportion N. If FB.Sensitivity analysis of entclass1pt{minimaentclass1pt{minimaTo analyze the impact of the penalty for losing one passenger on the route adjustment scheme, a sensitivity analysis of To analyze the impact of passengers’ value of time on the route adjustment scheme, a sensitivity analysis of This paper proposed a three-step adjustment framework to actively mitigate the impact of rail transit construction on bus operations. In Step I, a criterion was developed for selecting bus routes which are significantly affected due to rail transit construction and necessitate being adjusted. In Step II, we designed the stop-skipping strategy and truncation strategy, and checked whether they are opportune to ameliorate the service of each affected bus route. In Step III, feeder bus services were further designed to guarantee spatial coverage nearby the construction area. A mixed-integer linear programming model was later developed to determine the optimal configuration of the feeder bus service.A case study based on the Sioux-Falls network was conducted to demonstrate the applicability of the proposed framework. The results show that the proposed adjustment framework can reduce the total cost of bus routes The method proposed in this paper is not only applicable to the adjustment of bus routes during the construction of rail transit but also can be applied to other circumstances such as road maintenance. The paper could be extended in the following directions. First, the feeder bus service may attract more passengers than the sum of the passengers on the initial lines. On the other hand, the environmental deterioration brought by rail construction may lead to the loss of passengers. The design of the bus adjustment scheme taking into account passengers’ perception of rail construction and the induced passengers by feeder buses is left for a future ongoing study. Secondly, more factors such as the evolution of passenger access/egress trips and the accessibility of bus services, as well as calibration/validation against real data could be taken into account.


Diesel fuel stability can be considered from many points of view, of which the two considered most important are stability in contact with the environment and internal stability. Fuel stability in touch with the environment is often defined as oxidation stability, of which measurement procedures are well developed. The presented paper shows that fuel’s internal stability can also be important. The internal stability of diesel fuel with the local use of thermal and ultraviolet radiation (UV) as degradation factors and fluorescence signals as a probe is presented in this paper. We show that the internal degradation of fuel with temperature use differs from that with UV and simultaneous both factors use. Our study shows that using temperature as a degradation factor introduces significant fluorescence fading. Moreover, the fluorescence signal restores significantly later than the sample stabilizes at room temperature. The novelty proposed based on examination is hybrid degradation and an examination cycle that enables the simultaneous use of degradation factors and fluorescence reading. For this purpose, a dedicated measurement setup of signal control and processing was constructed and programmed. The measurement procedure of the data series for specific wavelength enables calculation of signal shifts that allow the internal stability classification of diesel fuel samples in less than 30 min with the cost of a single disposable capillary probe and one polymer plug. Premium and regular fuel examination results show that internal fuel stability can be related to polycyclic aromatic hydrocarbons (PAH) concentrations and can be modified with dedicated additives. For users of automotive diesel (EN 590), the stability of its parameters is a crucial issue . Fuel stAutomotive diesel fuel consists of the fuel base, fuel improvers, and impurities. Standard fuel base components may include petroleum diesel (petro-diesel) and synthetic diesel (syn-diesel). According to the EN 590:2009 standard, the optional automotive diesel fuel components can consist of up to 7% of fatty acid methyl esters (FAME).Petro-diesel is produced in a refinery . Petro-dThe stability of PAHs in free form can be deducted from recommended storage conditions. They should be kept in a tightly closed container kept at room temperature. For example, naphthalene sublimes at room temperature. However, the rest of the listed PAHs are stable under standard laboratory conditions, but all PAHs can be oxidized . Some PASyn-diesel can be produced from any carbonaceous material based on pyrolysis, hydrotreatment, or gas-to-liquid conversion ,25. Syn-Bio-diesel components may include fatty acid methyl esters (FAME), hydrogenated vegetable oil (HVO), or raw vegetable oil ,29. FAMEDiesel fuel often contains additives. Detergents and dispersants are the most crucial performance additives . The funDiesel fuel may contain contaminations, such as water, waxes, microbes, and particulate matter ,38. DiesAutomotive diesel fuel is a liquid mixture of liquids and particle components. This mixture’s main components are chemically stable hydrocarbons, but some active components, such as FAME and PAHs, are allowed in limited concentrations . The basIn everyday language, a chemical substance is stable if it does not react with the environment and is not internally self-degradable. In particular, the expected usefulness should be retained under standard storage conditions, including air, moisture, and exposure to temperature and light. Chemical stability, when used in the technical sense, means the thermodynamic stability of a chemical system. Thus, chemical stability can be defined in closed chemical systems, referred to as internal stability, or in open systems that are in contact with the environment ,47.The typical reactions that occur during diesel fuel storage, caused by contact with the environment, are hydrolysis, microbial growth, and oxidation. Hydrolysis happens when the fuel is exposed to water that has entered the tank with air, a situation described by relative humidity. The visible results of diesel fuel hydrolysis are a change in fuel coloration and sludge present at the bottom of the tank . MicrobeImpurities from the refining process, as well as from the bio-diesel components treatment, result in the degradation of the fuel ,53,54. MPhysical fuel stability is often related to the colloid (emulsion) form of liquid that results in phase separation and sedimentation processes. The proposed reaction type that results in sediment is due to phenalene (PAH) converted to phenalenone, which reacts further . PhotophPhysical parameters of colloids, including phase stability, can be examined with the use of an optical sensing method, such as UV-VIS, spectroscopy, turbidimetry, and dynamic light scattering ,61,62,633 and 32 g/mol; thus, we obtained 0.044 mols of oxygen. The conclusion of comparing the number of mols of oxygen and the unsaturated hydrocarbons is that oxygen can react with about 1% of fuel hydrocarbon components. Thus, direct fuel oxidation with an unlimited oxygen supply is just a model-type measure of an automotive diesel fuel’s actual stability.The degradation factors can be of chemical and physical type. The most intuitive chemical degradation factor is the presence of oxygen. Still, its volume is limited as modern automotive fuel systems, and storage tanks are effectively sealed to limit evaporative emissions. Therefore, oxidation of fuel is possible with oxygen present in the tank. Assuming that a 10-L tank is half filled with fuel, we obtain 5 L of fuel and about 1 L of oxygen. Thus, 5 L of fuel with a density of 0.85 kg/L gives 4.25 kg. Assuming cetane as a representative hydrocarbon with 226.44 g/mol, we obtain 18.76 mols of fuel particles. Considering that 25% of fuel particles are chemically active, the result is 4.69 mols of active particles. Parameters for oxygen are density 1.429 kg/mInternal chemical contaminations can significantly impact fuel stability; thus, they can be considered indirect degradation factors. Activating reactions of contaminations with unsaturated hydrocarbon components sometimes require energy, and the energy type can be viewed as a degradation factor ,67.The most intuitive physical degradation factors are UV radiation and temperature.It was shown that UV irradiation impacts diesel fuel’s chemical composition and selected physicochemical properties . The temAutomotive diesel fuel may be described as a heterogeneous reactive mixture with the chemical stability of a kinematic and a thermodynamic type . MoleculAs of today, used automotive fuel stability testing standards are not suitable for implementation in sensors, and a new method is required. While methods of oxidation stability are well described, the practices of fuel internal stability testing are in the initial stage of investigations. To examine the internal stability of fuel, the realization of reproducible and fast energy transfer methods to fuel samples is essential. Such energy transfer can be performed with the light irradiation of fuel closed in the transparent and thin walls of a capillary positioned over micro-heaters . A similThis paper presents new results of examinations of the internal stability of automobile diesel fuels with the simultaneous use of two degradation mechanisms: thermal and UV. The correct simultaneous application of degradation factors and fluorescence reading is not a trivial task since, during intensive heating and lighting of the sample, partial and temporary fading of the fluorescent signal informing about the state of the fuel is to be expected. In addition, the requirement of the time necessary to regenerate the signal is presented. The novelty of the proposed method is also in the construction of a measuring system that enables quick changes in the fuel state and synchronization of degrading factors with the test signals that induce fluorescence at the appropriate moments.The paper is organized as follows: Samples of commercial, automotive diesel fuels that meet EU standards from the same manufacturer of regular and premium quality fuel were used in this study. The time sequence of the investigations is presented in Premium fuels of summer type were subjected to a long-term degradation test in the optical darkroom, The fuels were poured to the same level and stored in closed jars and opened glasses. Sealed fuels seem not to be degraded. Their color, as well as transparency, are unchanged. Samples with free access to the atmosphere broke down completely. Color changes and deposits are visible. Some of the fuel evaporated. Interestingly, it seems that the effect of long-term oxidation does not depend on the type of fuel tested.According to the manufacturer, the main difference between summer and winter types of fuels was in used additives that change the structure of paraffin crystals, and thus the temperature blocking the cold filter (CFPP). The parameters of the fuels in the summer version and corresponding measurement standards are presented in The fuel samples were used unmodified and modified with an additional commercial multipurpose enriching additive, which extends engine life by cleaning and protecting against sludge formation in the fuel line. This additive was selected on the assumption that sludge formation is one of the leading indicators of fuel degradation. It is, however, challenging to choose the additive for a particular diesel fuel to achieve the expected fuel stability . The staThe proposed method of stability testing based on the observation of results of diesel fuel degradation in a capillary stored on the lab windowsill and exposed to variable temperature and lighting for one year is illustrated in The photodegradation of fuel samples at air contact can be explained as the result of UV radiation absorption by a PAH molecule that is subsequently transferred to molecular oxygen dissolved from the air. This process generates highly reactive singlet oxygen atoms, which results in a series of specific reactions and degradation products. These products are not characteristic of a diesel fuel’s internal stability. As PAH inside a sample absorbs UV energy, it can also be transferred to other molecules that form free radicals that can join other PAH molecules forming substituted aromatics and causing subsequent formation and growth of other PAHs. Besides basic PAHs, alkenes and complex PAHs, such as 2-methylnaphthalene or butylbenzene, can react under UV radiation, influencing fluorescence. Thus, PAHs and alkenes may be a reason for sediment growth in the fuel sample, as presented in It is evident that internal fuel degradation is a natural phenomenon and cannot be omitted when fuel stability is examined. The task of internal stability examination can be realized with a capillary optrode that provides protection of a section of the fuel sample from direct contact with the environment but enables fuel sample local degradation with UV and thermal radiation. The idea of diesel fuel internal section exclusive degradation with heat is presented in Capillaries used as optrodes were of the CV7087 type made from clear fused quartz by VitroCom, with lengths of 100 mm. The examined fuel sample was positioned in the capillary with the plug and by capillary forces. The fuel inside the capillary can be ordered into three sections, including two separation sections and a section under local degradation. The heat from the micro-heater concentrates in its close area . The degThe idea of diesel fuel internal degradation with UV radiation and the reading of degradation results is presented in The UV degradation factor must consider the Earth’s surface radiation by the sun . That meThe measurement setup is built using standard commercial optoelectronic modules and a house-made head; it is presented in The personal computer (PC) controls the experiments and data collection. The DasyLab software is used to control the degradation factors and data synchronization. The SpectraSuite software is for spectral data acquisition from Ocean Optics spectrometer HR2000+. DasyLab and SpectraSuite run simultaneously. DasyLab is equipped with a dedicated multipurpose script named DMPS. DasyLab measurement control is realized in hardware with the use of card USB-4716 from Advantech.The LED M365FP and LED driver DC2100 were used as the UV (365 nm) source. The LED current limit was set to 50 mA. The measurement system controls the operation of the UV source directly with a triggering signal and monitors it with the amplified detector PDA36A and with a fiber bundle probe RP20 use. The fiber bundle probe consists of an arm to carry light from a LED source to a head and an arm to bring light to the detector. The optical power delivered by fiber to the head was 1.6 mW.The optical signal is transmitted from the head to the HR2000+ spectrometer with the patch cord P600-1-UV-VIS. The DMPS also controls the spectrometer and SpectraSuite software’s work by triggering the acquisition signal. The integration time of spectra data is set in the software to 50 ms.The DMPS is also equipped with a proportional–integral–derivative regulation section. It controls the micro-heater through the electric power unit consisting of the programmable power supply type HM8143 and the reference power resistor that acts as a current probe enabling the stabilization of temperature generated at the micro-heater’s surface to 90 ± 0.5 °C. The temperature of the fuel sample in the capillary above the micro-heater stabilizes in about 15 s.The schematic of the head is presented in The base of the sensor head is made of alumina, its diameter is 7 cm, and its height is 5 mm. V-groves with uniform cross-sections were used to position the optical fibers and the optrode on the base. Capillary sections used as optrode were CV7087 from VitroCom, with an outer diameter of 870 µm. As the optical fiber outer diameter must be as close as possible to the capillary optrode, thus the optical fiber FG550UEC was used. Fiber buffers were removed for positioning purposes. To secure the fibers in the base and enable appropriate optical signal coupling, a short section of capillary TSP700850 from Polymicro with an outer diameter of 850 µm and inner diameter of 700 µm was used as a fiber’s buffer replacement. The head base was mounted on the aluminum heat sink, with triple the area of the base with 2 mm high copper spacers that enable the movement of air in the head. The head was mounted in a black plastic box 14 cm in height, 26 cm wide, and 45 cm long, with a removable cover, SMA fiber connectors, and culverts for power wires.Preliminary tests determined the fluorescence emission bands and the repeatability of the fuel sampling method. Since the fluorescence emission signal can vary in time, the fluorescence signal was recorded for 50 ms after 30 s from the UV source and was turned on in subsequent experiments.The first study, shown in On the left side of Fluorescence spectra changes introduced by the photodegradation of fuel samples can be observed in The initial characteristics of one day of photodegradation are presented in The repeatability of the experiment was tested using premium fuel that was stored for a week in a glass placed in a black box mounted on an anti-vibration base. This experiment enabled the analysis of fuel sedimentation. The signals recorded for samples taken from the upper, middle, and the end of the lower layer are shown in Characteristics from 380 nm to 550 nm increase with the sampling depth, which indicates fluorescence particle sedimentation. Interestingly, the signal of the microorganisms is not sensitive to sedimentation, which can be explained by the fact that they were alive and mobile or had a neutral buoyancy in the oil. Thus, in the following experiment, fuels are probed from the middle layers of the samples.Photodegradation tests use UV signals simultaneously as a degradation factor and fluorescence probe. Such tests allow flexible organization of the sampling time, but the collected characteristics are subject to varying degrees of fluorescence signal decay. Therefore, the relative change in the spectral features is essential information here.Observation of the spectral changes of the signal during the photodegradation of the regular fuel of unmodified and winter type with constant irradiation and reading with a 5-min sequence is presented in First, signals’ initial and rapid changes are observed at a wavelength from 380 nm to 430 nm, while slower changes are present in the 430–550 nm band. These changes seem to have minima and maxima, and the peak fluorescence signal is variable. The degradation results are visible after several min.Analogous examination with a 1-s sequence of sampling for premium diesel fuel of unmodified and summer type are presented in The characteristics set from A repeatable procedure with a precise timestamp of signal acquisition is essential for diesel fuel stability testing using UV as a degradation factor and examination probe. Analyzing complete spectral data of fluorescence changes versus time is a complex task. Thus, the following sections present the investigations of time-dependent signals at a specific bandwidth. The bands are of ±5 nm width and are positioned at potentially interesting wavelengths: 380 nm, 390 nm, 410 nm, 430 nm, 490 nm, and 500 nm of the dominant hills of examined fuels, as well as the dominant 675 nm band of the microbial presence.The measurement setup enables continuous and modulated degradation of fuel samples with thermal and UV radiations and simultaneous examination of fuel degradation with UV-excited fluorescence in programmed measurement cycles. The measurement cycles used in this publication are called DCE (degradation continuous and examination) and DME (degradation modulated and examination). It should be noted that light switching requires up to 2 s, while sample photoactivation, as well as the time of sample cooling and heating, is characterized by a similar time.This section aims to exhibit the vital phenomenon of fluorescence signal fading in examining fuel using temperature and UV as continuous degradation factors. The cycle using only UV radiation for continuous degradation and studying its effects is shown in The modification of the analyzed cycle was realized with the addition of UV switching off for 1 min at the end of 30 min degradation cycle and then again switching on. In The degradation with thermal radiation is made in the cycle named DCE:UVoffTon. It should be noted that thermal degradation requires UV light as the examination probe of degradation, as presented in The thermal fading of fluorescence is visible at the beginning and at the end of the experiment. At the start of the experiment, when the sample is at room temperature, the fluorescence signals are higher than after one minute of heating—switching on UV radiation and examination of fluorescence in the following 1-s results in a local signal increase, The maximum fluorescence signal for the tested fuel in both degradation cycles, shown in Unwanted fluorescence fading can also arise when UV and thermal radiation are used simultaneously. The corresponding cycle DCE:UVonTon is presented in The fluorescence fading is visible in In the above-presented cases, the comparison of degradation factors efficiency is loaded with uncertainty caused by potential fluorescence fading. Thus, based on the time that is required for the sample to return to the ambient temperature and fluorescence regeneration, which is less than one minute, two more measurement cycles based on double modulation are proposed. The first modulation involves excluding degradation factors after 5 min for 1 min. In this minute, the second modulation of light switching with a period of 5 s is used for degradation examination. Thus, the degradation and sample regeneration are equal in the subsequent cycles, and the action of signal fading on reading results is limited. Consequently, spectral data were collected in packets every 6 min. Thus, the proposed cycles allow the comparison of the effectiveness of degradation.The degradation and examination cycle with double-modulated UV radiation, named DME:UVonToff is presented in Comparing results obtained in DCE:UVonToff  and DME:The modulated cycle of degradation using thermal radiations for degradation and modulated UV for examination, named DME:UVoffTon, is presented in From The modulated cycle of degradation using thermal and UV radiations for degradation and modulated UV for examination, named DME:UVonTon, is presented in The degradation cycle results presented in Results collected in The ultra-short-term shifts in the 670 nm band are much more significant than in the short-time test. Thus, the interim conclusion is that microbial contamination is effectively reduced in proposed degradation cycles at their initial ultra-short-term stage. Therefore, the proposed method is not valid for testing the effect of microbiological contamination on the internal stability of the fuel.The previously presented degradation cycles have, in all cases, pairs of advantages and disadvantages. Obtained results show that both degradation factors are important to fuel internal stability; both ultra-short- and short-term data are essential, and thermal fading adversely affects the measured signals. The solution seems to be a hybrid degradation and examination cycle presented in Obtained time series are of the expected course, as presented in The hybrid cycle DHE:UVonTon is proposed for further tests of fuel samples with UV and temperature as degradation factors.The fuels presented in The signal at 490 nm is higher for regular than premium fuels samples listed in Collected data of initial signal shifts calculated between maximum values S(max) and semi-stable values assumed to happen at 200 s of the cycle, S(200s), are presented in Since the relation of signal shifts at all selected bands is similar in the sample-to-sample comparison, the average value can be assumed to measure signal changes. This measure supposes that in the ultra-short-term examination, the internal stability is lower in the case of regular fuel than of premium fuel. Moreover, the initial internal stability was increased in both fuels by the applied additive. This agrees with the observation of In stabilized situations, internal stability should be correlated to stable signals. The degradation factors should force fewer changes in signals for stable fuel than unstable. Collected data of the second part of the examination and degradation cycle corresponding to signal shifts calculated between values S(360s) and the end value of process in 1800 s, S(1800s), that are not burdened with signal fading are presented in The data show that medium-term internal stability is also more excellent for premium fuels than for regular fuels, but some differences in signals at specified wavelengths occur. The analysis of the internal stability of modified fuels confirms, sometimes postulated thesis, that modification with the active ingredient may result in additional, unexpected further reactions that are difficult to predict.Most significantly, the average short-term signal shift relation between premium and regular fuel is 1.07 , while tA summary analysis of the experiment can be made with cluster analysis. The corresponding dendrograms for wavelength shifts of data collected in Cluster analysis shows that premium fuel remains premium during degradation regardless of the permissible modifications. The same applies to standard fuel. It can therefore be stated that the proposed measurement procedure does not introduce unexpected errors. Thus, comparing the results of signal shifts for different fuels can serve as a differential classification for the internal stability of the fuel under testing. The fuel is more stable when signals of shifts S(360s)–S(1800s) are lower than in the compared sample. Fuel also is expected to be more stable when signals shift S(max)–S(200s) of initial degradation is more significant than in the referred sample.In the presence of oxygen, automotive diesel fuel degrades significantly. However, automotive diesel fuel samples without contact with oxygen can also degrade. We presented the results of the examination of internal fuel stability with the separate and simultaneous use of two degradation factors of thermal and UV radiations as they can be applied without physical contact and the use of any chemical reagents.We have shown that such examination is possible when fuel is positioned in a glass capillary optrode so that the outer sections of the fuel fill the capillary, preventing the middle section from direct exposure to the atmosphere. We have shown that the continuous temperature degradation factor results in significant fluorescence fading and can prevent proper examination. Thus, we conclude that realizing degradation with two degradation factors, such as temperature and UV radiation, is not a trivial task.From the point of view of the internal stability of the automotive diesel fuel, microbiological contaminants are positioned at the fuel–oxygen–water interface, so they are present inside the sample in limited concentrations. Moreover, UV radiation has a deadly effect on microorganisms. Thus, fast signal fading from live microorganisms is a side effect of the analyzed method.Examination of different fuels with continuous UV degradation leads us to the conclusion that specific characteristics of fluorescence may differ significantly. Moreover, fluorescence peaks during degradation may shift in value and wavelength. Thus, signal shifts at specified wavelengths are not a good measure of fuel stability, and the signal shifts should be measured in bands. In examined cases, the bands with 10 nm fulfill the task. It should also be noted that the fluorescence signal restoring from fading in explored cases is at the rank of 50 s while the time stabilization of the sample in heating and cooling is less than 15 s. Additionally, the time of the UV source activation is not to be omitted.Realized operational research of degradation cycles leads us to a hybrid degradation cycle that is a mixture of continuous 300 s ultra-short-time section and modulated 1500 s short-time degradation. This way, the proper reading of degradation results is possible. Measurement setup enables constant access to information in an ultra-short period of 300 s and the semi-continuous reading of short-term degradation. This hybrid cycle contains complete information on the degradation. Using it allows proper classification of the internal fuel stability with photoactivation time as its ultra-fast signal shifts as well as its short-term signal shifts in the range from 360 s of degradation to the end value of the cycle in 1800 s.Thus, well-defined time synchronization of degradation action and its results reading is required, and the realization of examination involves quite a complex measurement setup. Again, these are costs of any chemical used, and no initial sample is prepared for internal stability testing of automotive diesel fuel.Temperature and UV degradation factors act differently on the sample.At the same time, the action of both factors cannot be presented as the sum of two independent actions.The UV degradation factor acts stronger than temperature, but both factors simultaneously used are the key to the speed and effectiveness of examinations.The internal stability of automotive diesel fuel is related to the presence of unsaturated components and can be characterized by fluorescence signal shifts.The internal stability of diesel fuel is more related to the proposed method than to the standard measurement of oxidative stability.The proposed procedure and setup enable the comparison of different fuels’ internal stability using reference data. This comparison allows us to point to more internally stable fuel.The short list of the practical side of the investigation is as follows:Thus, as the main practical result of the research, we propose the differential classification of the internal stability of fuels that may be included in future commercial specifications and fuel parameters guarantees. Future examinations can be oriented toward validating the proposed method.


Monitoring and tracking issues related to autonomous mobile robots are currently intensively debated in order to ensure a more fluent functionality in supply chain management. The interest arises from both theoretical and practical concerns about providing accurate information about the current and past position of systems involved in the logistics chain, based on specialized sensors and Global Positioning System (GPS). The localization demands are more challenging as the need to monitor the autonomous robot’s ongoing activities is more stringent indoors and benefit from accurate motion response, which requires calibration. This practical research study proposes an extended calibration approach for improving Omnidirectional Mobile Robot (OMR) motion response in the context of mechanical build imperfections . A precise indoor positioning system is required to obtain accurate data for calculating the calibration parameters and validating the implementation response. An ultrasound-based commercial solution was considered for tracking the OMR, but the practical observed errors of the readily available position solutions requires special processing of the raw acquired measurements. The approach uses a multilateration technique based on the point-to-point distances measured between the mobile ultrasound beacon and a current subset of fixed (reference) beacons, in order to obtain an improved position estimation characterized by a confidence coefficient. Therefore, the proposed method managed to reduce the motion error by up to seven-times. Reference trajectories were generated, and robot motion response accuracy was evaluated using a Robot Operating System (ROS) node developed in Matlab-Simulink that was wireless interconnected with the other ROS nodes hosted on the robot navigation controller. The high interest in the analysis of the performances of Omnidirectional Mobile Robot (OMR) navigation platforms is increasing in the scientific community ,2,3, as Currently, the main attention in the advanced mobile robots research field is paid towards transitioning from automated guided vehicles to autonomous mobile robots. This technological challenge is sustained by developing complex sensors and computational processing power, which offer new navigation capabilities in a dynamic environment with predefined or variable constraints ,3,7.The prediction is that over four million logistical robots will be developed and placed in approximately 50 K warehouses by 2025 . The favPath performance evaluation based on odometry is inconclusive due to the mechanical shortcomings of the experimental OMR, even if the control action is well defined. Furthermore, the main concern related to the errors that appear in the localization of the robot is also justified by the fact that the OMR is intended to work in a dynamic warehouse environment. Even if the improvement of odometry by proper calibration reduces the position errors, the accurate knowledge of the current location can be ensured by an Indoor Positioning System (IPS).In this research study, the data acquisition from the IPS was exploited in order to monitor the motion response of the OMR and calculate the calibration parameters. Experiments involving typical motion paths for the OMR were performed, so that the longitudinal, lateral, rotational, and composed motions were studied in order to establish the calibration requirements for the kinematic transformations used for commanding the motion of the OMR and monitoring its actual execution.Tracking performance evaluation scenarios for composed motion reference trajectories having Lissajous curve shapes are comparatively analyzed both from the IPS and estimated odometry position . In the The architectural concepts together with the basic description of an omnidirectional embedded real-time robotics system was developed by the authors in the current research project, ROSY-LOGISTIC, and the main results were published in previous articles ,12,13. WThis research tries to capture as comprehensively as possible, in a first phase, the necessary steps for the IPS ROS node integration in the Matlab environment, since these steps are not completely described in the technical literature; thus, for anyone, this can be a time-consuming step. Further in The accurate knowledge of the current localization and orientation of the mobile robot can benefit largely from a well-calibrated odometry. In outdoor applications, Global Positioning System (GPS) technology offers good positioning accuracy and is used in many automated driving applications. Unfortunately, for indoor localization, GPS technology cannot offer similar reliability because the signals of the satellites lose much strength when penetrating a building.Low-cost technologies such as WiFi, ZigBee, and Bluetooth Low-Energy (BLE) are radio-frequency-based systems and are widely used in in mobile robots for indoor localization ,15. AlthUltra-Wideband (UWB) has gained interest in indoor positioning of robots, the system relying on the signal travel time for the distance between the mobile robot and static anchors. The mobile robot location is estimated by exploiting approaches such as multilateration and trilateration . In the There are several approaches for IPSs with their own advantages and limitations . UsuallyThe mobile robots’ cost increases significantly with the addition of advanced sensors, but odometry and calibration methods can definitely mitigate the positioning error.This work comes as a natural continuation of the previous work  of the oThe main contribution of this paper concerns the OMR localization accuracy analysis and proposing a new offline method for the OMR kinematics experimental calibration. In this regard, the effectiveness of the method was verified by comparing the performances between the reference trajectory and the estimated position.The position provided by Marvelmind was compared to a separately implemented position calculation based on raw point-to-point distances reported by the IPS to evaluate its reliability. The initial OMR trajectory tracking was evaluated, and in addition to the translation velocity correction coefficients , the neeThe OMR consists of a chassis that contains the set of mechanical elements including the propulsion system, made up of four motor–planetary gearbox assemblies, coupled to the chassis through eight shock-absorbing suspensions, which ensure contact with the ground, at any time, for the four Mecanum wheels, which have a diameter of 6The driving structure was implemented hierarchically, with a top-down approach, with two controllers: vehicle controller (executive-level) and navigation controller (high-level). The vehicle controller was implemented with an STM32F103RC micro-controller, while the navigation controller was implemented with an NVIDIA Jetson Nano B02 embedded system. The two control systems are directly connected to various components of the robot, as represented in Given the complexity of the software needed in a dynamic environment, a certain degree of computational resources is required. The path-planning algorithms need to be implemented in order to be executed completely on the OMR platform, without the help of external or remote control.J is the inverse kinematic Jacobian matrix of the OMR—expressed in relation to the notational conventions of the OMR elements:On the low-level controller runs a customized implementation of FreeRTOS. The firmware includes the inverse and direct kinematics models with all specific OMR parameters. As was demonstrated and detailed in , the matAll variables and their numerical values for the experimental platform from Equations –3) belo belo3) bThe way to determine the lateral/longitudinal and rotation velocities of the OMR starting from each wheel’s velocity is known as forwarding kinematics and is used in odometry calculation—Equation :(3)vxvyΩIn an Ubuntu environment with popular programming languages and libraries such as C++, Python, OpenGL, and ROS, the navigation level of the OMR developed on the Jetson Nano, which comes with a Quad-core ARM A57 @ 1.43 GHz and 128-core Maxwell GPU, providing enough resources to cater to the computation for mapping and motion planning.The IPS used with the OMR platform was developed by Marvelmind Robotics (Starter Set HW v4.9-IMU-NIA), with a promised accuracy of 20 mm , and canThere are two operation modes possible for the system, which are called the Inverse Architecture (IA) and Non-Inverse Architecture (NIA). In the IA, the stationary beacons emit ultrasonic signals, while multiple hedgehogs can receive them, the mode being more useful for small areas requiring a minimal number of fixed beacons in order to avoid the reduction of the localization rate. In the NIA, the mode used in the current research, the hedgehogs emit the ultrasonic signals and the stationary beacons receive the propagated wave, and if more hedgehogs are to be monitored in the same area, either Time Division Multiple Access (TDMA) or Multi-Frequency (MF) ultrasonic signals using Frequency Division Multiple Access (FDMA) can be configured for quasi-simultaneous and, respectively, simultaneous tracking. Using TDMA, multiple targets take turns in being localized. Using FDMA, the targets emit simultaneously, but on different ultrasonic frequencies. TDMA implies a reduction of the localization rate, while for FDMA, there is a limited number of frequencies that can be effectively identified using digital filters ,24 impleThe location of the OMR is calculated using a proprietary, undisclosed, trilateration algorithm based on the propagation delay, also named Time of Flight (ToF), of the acoustic signal between the hedgehog and up to four nearby stationary beacons of the reference network. The distances between beacons is recommended to be up to 30 m, achieving with just four stationary beacons a coverage area of up to 1000 mThe performance of the localization system depends on many aspects, and a proper configuration of the fixed beacon network is essential for achieving the promised accuracy. In real-world scenarios, it can be difficult to achieve the ideal conditions needed for proper operation. Based on the acquired experience, the localization rate decreases on so-called submaps (subareas covered by up to four fixed beacons), where the maximum distance between the beacons is larger. In a 2D configuration for a maximum distance of 5 m between any two beacons, localization rates of around and more than 25 Hz can be achieved. On the other had, 2D localization precision in systems using multilateration is subject to the Horizontal Dilution of Precision (HDoP) [The experimental OMR platform was equipped with the Marvelmind IPS in 2021, and since, then there have been roughly monthly updates of the firmware and software on the producer website, which keeps improving the solution. The latest version used in this study was 7.202 from the beginning of September 2022.marvelmind_nav Robot Operating System (ROS) package, in order to facilitate the usage of their IPS solutions in industrial and robotics applications. Since it is not yet a standard ROS package, it needs to be manually installed to be used on the OMR. A short summary of the installation steps [Open a command line on the target embedded computer;src) of the used ROS workspace;Change the directory to the sources folder : Install CMake 3.15.5 or newer ;Install Microsoft Visual Studio 2017 (VS17), especially the C/C++ development tools and the CMake support ;Install Python 2.7  ;Configure the Python version by executing in the MC (recommended immediately after restarting Matlab): addpath(‘C:\Program Files\CMake\bin’);Add to the Matlab path the binary installation folder of CMake, by executing in the MC: mex file type shared libraries with VS17 by executing in the MC : mex -setup:‘C:\Program Files\MATLAB\R2021a\win64\mexopts\ msvcpp2017.xml’ C++;Set up the Matlab compiler for building the msg from the root of the ROS Marvelmind package [.msg files;Copy in Matlab’s current path the folder  package  that conmarvelmind_ros_messages;Rename the locally copied folder to .mex files for supporting Marvelmind ROS messages by executing in the MC: rosgenmsg(‘./marvelmind_ros_messages’);Build the needed Matlab addpath(‘./marvelmind_ros_messages’);Include the folder containing the support files for custom Marvelmind ROS messages in the Matlab path by executing in the MC: savepath;Save the Matlab path for future restarts by executing in the MC: clear classes;Clear the Matlab workspace classes by executing in the MC: rehash toolboxcache;Refresh the Matlab toolbox cache in order to load the new message types by executing in the MC: Run the first step again to check that the new message types are now available to Matlab.The ROS node named  that do not need special support, but this path can be challenging also.In the initial investigation , a simplThe central part of the node is the position controller implemented as a Matlab function block. It was designed to steer the OMR to the prescribed pose received from the waypoint selector block, which keeps track of the current and next target waypoint on the trajectory path. Velocity saturation and acceleration limitation were applied to keep the OMR within nominal parameters and to minimize the risk of damaging collisions.In the command output stage, manual switches were included so that simple motions and emergency pauses could be requested when the node was executed remotely from a PC, connected through the WiFi network to the rest of ROS nodes running on the OMR. This approach allowed for accelerated testing and improved debugging of the developed node by using Matlab-specific tools such as signal probes and data recordings.With a setup similar to the one described in the previous subsection, some initial experiments were carried out using simple trajectories, such as a square shape , to inveIn At that moment, the quality stream of the Marvelmind IPS localization was not used; however, it became obvious that the configuration of the IPS beacons was not ideal, and in certain areas, some of the stationary beacons missed the direct signal from the hedgehog and received only indirect propagation reflected on nearby walls. This observations motivated a more careful approach to the placement of the IPS stationary beacons, but also the interest in monitoring the reported position quality and attempting an independent trilateration implementation based on the raw beacon-to-beacon measurements, which can be received from the IPS after each localization in order to obtain a quantitative assessment of the position accuracy.After implementing support for velocity reference compensations  at the eAnother issue that was identified after the initial calibration was an undesired rotation of the OMR while following the reference track. This aspect is not visible in Autonomous navigation benefits from the good accuracy of the motion and odometry. In this process, there are three contradictory requirement concerns: high accuracy, robustness for different conditions, and the application of cost-effective sensors and methods. Good performance can be ensured with high mechanical precision for the OMR, which implies higher costs. Better position-finding sensors can solve the positioning control using a closed-loop approach. This also leads to a higher cost, as well as lower robustness.In this context, a calibration method designed to compensate through software the undesired operation of the OMR due to mechanical imperfections is of interest since it can improve the base performance for motion- and odometry-based localization, which can only be useful for more advanced techniques such as sensor fusion.Considering the observed issues regarding the initial results obtained in the previous section, which used a complex control structure made of a path planner based on waypoints and a positioning controller, a simplified open-loop control structure was considered for further analysis and calibration of the odometry. In this way, attention can be concentrated on the performance of the OMR, while other possible sources of errors are limited. As a result, a scripted environment based on Python was developed to apply sequences of motion requests (as relative velocity vectors that the OMR platform can execute) and, at the same time, to record the reported odometry data and the localization information from the Marvelmind IPS for later analysis and calibration information extraction.In order to perform the experimental calibration of the OMR kinematics, certain practical challenges need to be taken in consideration and mitigated: mechanical accuracy and play of the OMR components, wheel slippage during aggressive maneuvers, floor quality, suspension response, integration errors, initial position, and orientation estimation. In this context, a practical approach needs to be constructed around simple operations that can be easily reproduced systematically, which motivated a simpler open-loop motion control solution. The entire experimental procedure followed the flowchart from In order to obtain good performance for complex movements, it is essential to obtain the desired response for simple orthogonal movements, i.e., pure longitudinal, lateral, or rotational motion, respectively, which are specific to the OMR. The research conducted on the OMR based on four Mecanum wheels showed that the direct usage of the mechanical parameters for solving the kinematic equations led to discrepancies, especially for the lateral and rotational motion. The observed motion errors can be classified into scaling errors (moving/rotating more or less than expected) and cross-talk errors .paired mobile beacons to establish the orientation of a target that carries them, the method was not pursued due to its additional setup complexity and also because the starter kit used contained only four stationary beacons; converting one of them to a paired mobile beacon meant a reduction of the fixed beacons used for the multilateration of the position.Depending on the type of motion error, different methods can be applied for experimental determinations. For translation scaling errors, a laser range finder was considered for measuring the actual motion due to its high accuracy. Alternatively, a well-set-up IPS together with an averaging strategy in specific reference points of a test path can be used to obtain a more complete picture of the actual motion in time. For rotational scaling error and the motion cross-talk errors, the methods were based on localization at relevant points from the reference trajectory using the IPS or the usage of the LiDAR to directly measure the orientation variation relative to some available reference . Although the IPS supports a special mode called An important aspect can be the order in which the motion errors are determined, especially because of the noticed cross-talk from translation to rotation motions. In this context, it is easier to first determine the scaling compensation required for the correct rotation and then attempt the determination for translation and the cross-talk between translation and rotation, which cannot be easily separated. By starting with the determination of the rotation correction factor, then the proper translation–rotation cross-talk factor can be directly determined.Depending on the amount of inaccuracy for the kinematics involved in rotation, an iterative practical approach may be required for easier determination. The technique for the iterations was similar, it being necessary in all cases to establish a reference direction, followed by a number of rotations in place, and then, after stopping, a final measurement of the orientation direction. The in-place rotation was executed by requesting the OMR platform to rotate at a fixed rate for the theoretical time needed to complete a specific number of rotations. Considering a firmware implementation on the OMR that limits the acceleration and deceleration to the same value to avoid slippage or over-currents, the previously described requested motion should be executed as expected.For example, in the first iteration, a single rotation was performed to obtain an initial estimation of the correction factor, which was then applied in the inverse and direct kinematic transformations. In the next iterations, the number of in-place turns was increased to benefit from averaging-out the errors, such as those affecting the measurement of the initial and final orientation.In the case that the IPS is to be used for determining the rotation correction factors, a method for evaluating the initial and final orientation is necessary if the paired mobile beacons option is not considered, as summarized in the left most (blue) column of To minimize the limitations of the IPS’s accuracy, the longitudinal translations are recommended to be as large as the area in which the IPS is least affected by the HDoP or other issues. In In a similar way, the kinematic rotation correction factor can be determined using LiDAR, in this case without it being necessary to perform the longitudinal motions to identify the initial and final orientation.As mention in , the traIn Under the assumption that the coupling between the translation velocities and the rotational velocity side effect is linear, the recording of the paths from the IPS correlated with the odometry, as illustrated in By using the IPS, the arc radii can be determined by fitting the recorded path with an arc and then determining its length. The method has the advantage of reducing the impact of eventual IPS measurement errors. The ratio between the odometry displacement and the arc length gives the inverse kinematic translation correction factor. The curvature of the arc, defined as the reciprocal of the arc’s radius, is the translation–rotation cross-talk correction factor used to calculate the compensation rotation velocity to obtain the desired straight motion. In order for the odometry not to measure the injected compensations, the direct kinematics need to be counter-compensated in reverse order with the reciprocal of the correction factors.S, a mid-point M, and the final point F. The disadvantage of the method is that if a mid-stop is executed to obtain an averaged determination based on the IPS, the orientation of the OMR is likely to slightly change and affect the determination. Using the coordinates of the three points, the center C and the radius R of the circumscribed circle can be determined analytically. Furthermore, using the known vertices of the triangle R.As an alternative to fitting, the arc radius can be determined by obtaining three accurate reference points along the track: the start point As a metric of performance, translation–rotation cross-talk deviations of up to 7 mrad mBy applying the previously described approach, the kinematic correction factors listed in In logistic systems and especially in the calibration phase of the OMR’s development, it is beneficial to use an IPS, and it is also essential to measure its accuracy. Considering the unavoidable position solution uncertainties due to the ultrasonic system setup, the manufacturer describes qualitatively the confidence of the latest position solution as a percentage. In the research context of OMR platforms, it can be more useful to obtain a quantitative estimation of the uncertainty that would ensure the assessment of each obtained positioning solution sample.Since there is no open information given about the position solution calculation method for the IPS used, to our knowledge, it became necessary to apply an external/parallel method to validate the offered position solutions, because during our experiments, significant deviations were observed in certain locations.Among the useful functionalities provided by the API, there is an option for obtaining the raw point-to-point distances between the mobile beacon (named the hedgehog) and each of the up to four fixed beacons in the current localization zone. Thanks to a relatively open approach regarding the parts of the communication protocols used and an extensive API, it is possible to develop external dedicated methods based on trilateration, methods that can also provide a better metric for assessing the accuracy.The mobile beacon, represented by the blue point in the configuration dashboard in In addition, the system outputs the position information for all the configured fixed beacons every 10 s, allowing for automatic map updating, which is useful for the external position calculation.i, i, and The positioning error is defined as in Equation  using thTrilateration was performed externally using an iterative implementation that searches for the coordinate pair Equation , which aAn example of the early attempts to track the calibrated lateral motion using the IPS and the external multilateration technique is depicted in In order to obtain smoother trajectories, in place of the generic trajectory controller developed using the Matlab rapid prototyping environment, which uses waypoints for navigation, a simplified open-loop trajectory generation was considered.S is a scaling factor . As a reference path for complex motion test scenario, a Lissajous-curve-shaped trajectory was chosen , describThe needed speed vectors that were applied to the OMR in order to obtain the desired motion, without using a position controller, were calculated using the derivative of Equation  with resEquation .(6)vx to achieve highly accurate, precise position and navigation data.The whole thread of the work was from the perspective of a systematic approach, the experimental design being a well-defined research methodology, useful to have greater trust in odometry.The future research direction involves GPS fused with an IMU, the sensor being slightly attached to the GPS in order to predict and update the vehicle position even in the event of GPS signal loss.