Large Travel Research Articles

Travel Distances for Interhospital Transfers of Critically Ill Children: A Geospatial Analysis.

The U.S. pediatric acute care system has become more centralized, placing increasing importance on interhospital transfers. We conducted a geospatial analysis of critically ill children undergoing interfacility transfer with a specific focus on understanding travel distances between the patient's residence and the hospitals in which they receive care. Retrospective geospatial analysis using five U.S. state-level administrative databases; four states observed from 2016 to 2019 and one state from 2018 to 2019. Participants included 10,665 children who experienced 11,713 episodes of critical illness involving transfer between two hospitals. Travel distances and the incidence of "potentially suboptimal triage," in which patients were transferred to a second hospital less than five miles further from their residence than the first hospital. Patients typically present to hospitals near their residence (median distance from residence to first hospital, 4.2 miles; interquartile range [IQR], 1.8-9.6 miles). Transfer distances are relatively large (median distance between hospitals, 28.9 miles; IQR, 11.2-53.2 miles), taking patients relatively far away from their residences (median distance from residence to second hospital, 30.1 miles; IQR, 12.2-54.9 miles). Potentially suboptimal triage was frequent: 24.2 percent of patients were transferred to a hospital less than five miles further away from their residence than the first hospital. Potentially suboptimal triage was most common in children living in urban counties, and became less common with increasing medical complexity. The current pediatric critical care system is organized in a hub-and-spoke model, which requires large travel distances for some patients. Some transfers might be prevented by more efficient prehospital triage. Current transfer patterns suggest the choice of initial hospital is influenced by geography as well as by attempts to match hospital resources with perceived patient needs.

A 3-DOF multi-depth-of-field carrier automatic focusing stage

Abstract Automatic focusing Stage is an important part of automatic focusing system, a 3-DOF (z-axis displacement and XY axis tilt) Multi-Depth-Of-Field Carrier Automatic Focusing Stage (CAFS) is designed, manufactured and tested in this paper. The stage is driven by four piezoelectric (PZT) actuators. Based on four bridge amplifying mechanisms, large displacement travel and tilt Angle are obtained. Compared with other focusing stages, the developed stage adopts the focusing mode of directly adjusting the spatial position of the sample to realize focusing, which not only avoids the inherent defects of objective focusing mode, but also has the advantages of compact structure, low shape and overall manufacturing. In this paper, the structural parameters and the overall design of the stage are determined, and then the characteristics of the focusing stage are finite element analyzed. Finally, the performance of the focusing stage is studied experimentally. The maximum Z-axis output displacement of the focusing stage is 213.5 μm, and the maximum X-direction and Y-direction tilt angles are 1.5 and 1.7 mrad, respectively. For the application of CAFS, the practicability of CAFS is verified by Z-axis image superposition acquisition method in automatic focusing system.

Design and study of a separated stick-slip piezoelectric actuator

ABSTRACT The stick-slip type actuator based on the stick-slip driving principle has the characteristics of simple structure, high precision, large travel and no electromagnetic interference. However, the stick-slip driving principle leads to the existence of the displacement backward phenomenon when it is driving in a single direction, which reduces the output performance of the driver. In order to solve the above problem, a stick-slip separated piezoelectric actuator with separable stator and actuator is designed by combining the advantages of lever mechanism and triangle mechanism in this paper, and theoretical calculations and simulations on the flexible hinged amplification mechanism are carried out. The prototype of the stick-slip separable piezoelectric actuator is made, and the output characteristics and speed characteristics of the actuator are experimentally tested to determine the optimum voltage and frequency values for practical operation.

Exploring Veterans' Experiences Accessing Chronic Pain Treatment in the VA Community Care Network.

Chronic pain is common among Veterans, and rural Veterans commonly struggle obtaining chronic pain care due to large travel distances to the nearest Veterans Affairs (VA) medical center. In 2019, the VA established the Community Care Network (CCN) to provide Veterans access to care in community-based settings, including chronic pain management. To explore the experiences of rural Veterans receiving chronic pain treatment in the VA CCN, including their perceptions about perceived barriers, facilitators, and benefits to accessing comprehensive chronic pain management. Qualitative study using semi-structured interviews. Ten rural Veterans receiving chronic pain management in the VA CCN took part in a qualitative interview focused on their experiences accessing and utilizing the VA CCN. A descriptive qualitative approach was used. Major themes were identified through thematic content analysis. Veterans described challenges navigating the approval process, finding approved CCN providers for pain management, and they perceived that communication between the VA and community providers was not seamless. Once enrolled in the CCN, however, Veterans valued the freedom to choose providers specializing in pain management within their local communities, timely access to appointments, and opportunities to explore a wider range of pain treatment options and alternative therapies, in addition to traditional medical interventions, all in their local community. As the CCN seeks to improve collaboration between VA and community providers, recognition of Veterans' experiences could serve to drive the development of network improvements. Findings reported here suggest that Veterans preferred obtaining care in the CCN once they could navigate administrative complexity to access it. Thus, efforts to streamline VA administrative requirements for initiating CCN care would better support Veterans in meeting their needs in this context.

Analysis of Stakeholder Engagement and Role in the Incentive Travel Destination Selection Process

Incentive travel tourists generally come in large groups and travel at the full expense of their company. Their expenditure is greater than ordinary tourists, but they receive less attention in Indonesia’s marketing strategy as quality tourists. This condition occurs due to a lack of understanding of the incentive travel business process. This lack of understanding is because research on the MICE industry is more concerned with meetings/conferences or exhibitions than incentive travel. Also, a reference book that discusses incentive travel and its relation to the choice of destination processes or destination marketing strategy is limited. This study aims to determine who is involved in the destination selection process and their relationships. The research method used is a qualitative method using desk research for data collection and content analysis for analytical methods. The research method used is a qualitative method using desk research for data collection and content analysis for the analysis method. Desk research was carried out by reviewing literature related to travel incentives and research report documents conducted by research institutions related to incentive travel. The result shows several parties’ engagement and role in the incentive travel destination selection process. Keywords: incentive travel, stakeholders, MICE industry, quality tourist, destination selection

Research on Output Characteristics of a Non-Contact Piezoelectric Actuator’s Micro-Displacement Amplifying Mechanism

A non-contact piezoelectric actuator is proposed. The non-contact power transfer between stator and rotor is realized by pneumatic transmission, characterized by fast response, long life, compact structure, and easy miniaturization and control. The structure of the non-contact piezoelectric actuator is designed and its working principle is elucidated. The equation of the relationship between the output displacements of the non-contact piezoelectric actuator’s micro-displacement amplifying mechanism and the input displacements of piezoelectric stack is deduced, and the simulation analysis method of output displacement of the micro-displacement amplifying mechanism is established. Using the equation and the simulation analysis, the output characteristics of micro-displacement amplifying mechanism for the non-contact piezoelectric actuator and their changes along with the system parameters are investigated. The detailed process of optimal design of the micro-displacement amplifying mechanism is given by means of mathematical statistics. The prototype is made and the performance test is carried out. The correctness of the theoretical calculation and simulation analysis is verified by comparing the experimental values with the theoretical and simulated values of the output displacement of the micro-displacement amplifying mechanism. The results show that the initial angle of bridge structure I has an obvious effect on the output characteristics of the micro-displacement amplifying mechanism in the range of 5°–15°. When the lever’s rod length is 13 mm–15 mm, the bridge structure II’s rod length is 6 mm–7 mm, and the power arm length of bridge structure I’s driving lever is 5 mm–7 mm, the bridge structure II’s rod horizontal projection length is 5 mm–6 mm and the output displacement of the micro-displacement amplifying mechanism is larger. Through the optimal design, it is obtained that the bridge structure I’s initial angle is 8°, the lever’s rod length is 15 mm, the bridge structure II’s rod length is 7 mm, and the power arm length of bridge structure I driving lever is 5 mm, the bridge structure II’s rod horizontal projection length is 6 mm, and the simulated output displacement of the micro-displacement amplifying mechanism is 0.1415 mm. The prototype test reveals that as the input excitation displacement decreases, the error increases, while as the input excitation displacement increases, the error decreases. Specifically, when the input excitation displacement is 0.005 mm, the measured output displacement of the micro-displacement amplifying mechanism is 0.1239 mm, resulting in a 19.8% deviation from the theoretical value and a 12.44% deviation from the simulated value. The research work in this paper enriches the research achievements of non-contact piezoelectric actuators, and also provides a reference for designing small structure and large travel micro-displacement amplifying mechanisms of this type of actuator.

Quick-connect scanning tunneling microscope head with nested piezoelectric coarse walkers.

To meet changing research demands, new scanning tunneling microscope (STM) features must constantly evolve. We describe the design, development, and performance of a modular plug-in STM, which is compact and stable. The STM head is equipped with a quick-connect socket that is matched to a universal connector plug, enabling it to be transferred between systems. This head can be introduced into a vacuum system via a load-lock and transferred to various sites equipped with the connector plug, permitting multi-site STM operation. Its design allows for reliable operation in a variety of experimental conditions, including a broad temperature range, ultra-high vacuum, high magnetic fields, and closed-cycle pulse-tube cooling. The STM's compact size is achieved by a novel nested piezoelectric coarse walker design, which allows for large orthogonal travel in the X, Y, and Z directions, ideal for studying both bulk and thin film samples ranging in size from mm to μm. Its stability and noise tolerance are demonstrated by achieving atomic resolution under ambient conditions on a laboratory desktop with no vibrational or acoustic isolation. The operation of the nested coarse walkers is demonstrated by successful navigation to a μm-sized 2D sample.

Application of adaptive inverse compensation feedforward—MPC feedback control to AFM piezoelectric micro-positioning platform

As the integral constituent of atomic force microscope (AFM), piezoelectric micro-positioning platform (PMP) plays an pivotal role in AFM working accuracy. However, the PMP platform has hysteretic nonlinear characteristics, which bring challenges to high-precision positioning applications, especially in large travel applications. In this paper, the nonlinear Prandtl–Ishlinskii (P–I) model and the linear auto-regressive with extra inputs dynamic model are cascaded to form the Hammerstein model to characterize the dynamic characteristics of PMP, and the mixed algorithm of the beetle antennae search-differential evolution is designed to identify the parameters of the established model. In order to eliminate the hysteresis effect, a compound controller based on adaptive inverse compensation is proposed, which is composed of feedforward controller of P–I inverse model and model prediction controller feedback controller. As the compound controller depends on modeling accuracy, the tracking error caused by model mismatch is improved by adaptive mechanism. The experimental tracking results of sinusoidal signals and triangular signals of different frequencies show that the proposed method can improve the tracking performance of PMP and verify its effectiveness.

An approach for crucial geometric error analysis and accuracy enhancement of gantry milling machines based on generalized correlation sensitivity

Geometric errors in gantry milling machines with long-span beams and large travel can seriously degrade workpiece accuracy. Sensitivity analysis and compensation of geometric errors with coupling and fluctuation can significantly improve the machining performance of machine tools. An accuracy enhancement approach for gantry milling machines is proposed in this paper. Firstly, the geometry error analytic fluctuation eigenfunctions are established by using the high-order Fourier series fitting. Secondly, a non-linear generalized correlation analysis model is proposed to identify the crucial errors that significantly affect the machining accuracy. Thirdly, the motion commands compensated for geometric errors are calculated. Specifically, compared to traditional inverse kinematics, the proposed error compensation process is simple and suitable for most machine tools with orthogonal linear axes. Finally, comparative cutting experiments are performed. The accuracy of the test piece is improved by approximately 34.7 % with error compensation. The effectiveness of the proposed method is validated.

Design and experimental study of a planar piezoelectric actuator with resonant actuation

Planar piezoelectric actuators, which can achieve high-precision motions over a wide range, have been widely applied in high-end equipment fields. However, the existing planar piezoelectric actuators can no longer meet the high actuation characteristics required for the rapidly development of these fields, which include large travel, high resolution, fast speed, planar three degrees of freedom (3-DOF) and a compact structure. A planar piezoelectric actuator with resonant actuation is proposed and tested in this work. The actuator consists of four symmetrically configured uniform bending-bending hybrid piezoelectric units, which coordinate to achieve large travel and planar 3-DOF characteristics. A vibration isolation mechanism adopting thin beam structure with low stiffness in coupling directions is designed to achieve vibration isolation among the units. The actuator can operate in high frequency resonance mode and low frequency stepping mode, allowing for the achievement of high-speed and high-resolution characteristics. A prototype is fabricated and tested. A compact structure measuring 53 mm × 53 mm × 13 mm and weighing only 30.2 g has been achieved. The maximum linear and rotary speeds have been tested to be over 400 mm/s and 13 rad/s, respectively. The linear and rotary resolutions are 0.42 μm and 12.9 μrad, respectively. The proposed actuator achieves characteristics of large travel, high resolution, fast speed, 3-DOF and a compact structure.

СОВЕРШЕНСТВОВАНИЕ ПАССАЖИРСКИХ ПЕРЕВОЗОК В Г.БРЯНСКЕ С ИСПОЛЬЗОВАНИЕМ ЭЛЕКТРИЧЕСКОГО ТРАНСПОРТА

The paper considers the state of the issue of improving the route network of the town of Bryansk and possible directions of their improvement. It analyses the variants of existing bus and trolleybus routes and reveals the routes with high degree of duplication. It is suggested to change the duplicated routes using trolleybuses with the dynamic charging and having a sufficiently large autonomous travel reserve. The possible reduction of total mass emissions of exhaust gases and significant reduction of operating costs in case of application of trolleybuses with dynamic charging is determined.

Workshop Synthesis: Mixed Modes and Devices - Integrating Technology into Traditional National Travel Surveys

This paper is a synthesis of discussions and findings from an in-depth six-hour workshop. Household travel surveys are expensive and are seeing a drop in response rates all over the world. The situation has worsened with the COVID-19 pandemic. In this context, mixed-mode surveys and new technologies are getting increased attention as ways to complement traditional household travel surveys designs. But many challenges remain. The objective of the workshop is to discuss the potential and known impacts of new technologies on large household travel surveys, to characterize bias generated by mixed modes frameworks, and to document different perspectives in an uncertain context.

Организация мелкосерийного производства деталей на принципах модульной технологии

It is emphasized that the traditional job shop production is characterized by low efficiency due to the use of superuniversal machining facilities for their underemployment of performance capabilities at work and also low-productivity of process flowsheet when machining part surfaces as a sequential surfaced job, the organizational form of production in the form of sections by type of machine tools, i.e. a section of lathes, a section of milling machines, etc. It results in large travel length of workpieces in the machining process at work. The desire to increase the efficiency of production by organizing launch of batch workpieces that are formed in a constructive similarity, such as structures, parts of rotation body types, etc., does not have a significant effect, because the task is just minimizing the run time spent on changing fixtures and reinstalling workpieces, but not taking into account an optimal sequence of parts in the batch. For increasing the efficiency of small-scale production, the module technology is proposed. The main idea of it is to represent the part not as a network of separate surfaces, but as surface modules, where the surface module is understood as a combination of surfaces and the part performs its proper function with the help of this module. This enables a good specialization of workplaces that are organized not for processing methods, but for manufacturing the appropriate groups of surface modules. The latter make it possible to take advantage of a more productive process flowsheet for machining part surfaces. It is sequential parallel surface job that is used. When organizing production, it becomes possible to use the layout of workplaces in line according to the in-line method, which will significantly reduce the part travel length at workplaces.

Modelling and Analysis of Dynamic Servo Error of Heavy Vertical Machining Centre Considering Nonlinear Factors

The dynamic servo error of heavy-duty vertical machining centres is one of the decisive factors affecting the machining accuracy of large and complex parts. Due to the characteristics of large mass, large load, and the large travel distance of the machine tool, non-linear factors such as friction, backlash, and lateral shift are more likely to cause unstable behaviours such as stick-slip and oscillation of the servo feed system of the machine tool, and reduce the performance and servo accuracy of the motion axis. In this paper, to consider the influence of non-linear factors such as friction, backlash, and lateral shift, an appropriately simplified representation of the mechanical transmission system of the ball screw has been used. According to the control structure of the Siemens 840D numerical control system, a theoretical model of the servo feed system for the heavy-duty vertical machining centre was established based on three-loop control. Then, the single-axis and double-axis closed-loop simulation models of the servo feed system were built in Simulink, and the influence pattern of control parameters and nonlinear factors on the dynamic servo error was obtained through simulation analysis. Finally, the validity of the theoretical model for the servo feed system was verified through a comprehensive comparison of simulation and experimental outcomes. This encompasses an analysis of the control system Bode plots, critical stick-slip velocity, and tracking errors in the X-axis with linear motion. The validation provides theoretical guidance for parameter design and mechanical adjustments of the servo feed system in heavy-duty vertical machining centres.

Quantifying the Travel Undertaken by Cancer Patients Receiving Radiotherapy in Victoria, Australia

This study aimed to investigate the travel distance for cancer patients treated with radiotherapy in Victoria, Australia, during a 9-year period relative to their home address. Additionally, the study aimed to quantify 'excess' travel distance where patients travelled to treatment centers that were not their closest. The PRedicting the health economic IMPact of new and current CAncer Treatments (PRIMCAT) dataset was used for the study. PRIMCAT is a multi-institution research initiative taking a data-driven modelling approach to understand and forecast cancer treatment utilization in Australia. The PRIMCAT dataset is a comprehensive linked dataset including a retrospective cohort of patients 18 years and over, diagnosed with cancer included in the Victorian Cancer Registry between January 2010 to December 2019. For each patient in the cohort, data linkage includes a range of datasets managed by state and federal health departments including the Victorian Radiotherapy Minimum Dataset. A distance matrix was constructed using the Google Distance Matrix API that included driving distance between postcodes of selected patients and the postcodes of radiotherapy facilities. The centroid of each post-code was used for driving distance measurements. We first analyzed the realized travel distances of patients followed by the excess travel by patients. The excess travel was further quantified separately for public and private radiotherapy facilities. There were 86,408 unique patient-radiotherapy courses available and of sufficient data quality to analyze. Patients travelled an average of 42.5km (s.d. = 72.2km) one-way, with a median travel distance of 16.5km. The largest distance travelled was 723km with 95% of patients travelling between 0km and 257km. Of the patients who received radiotherapy in a public facility, 44.3% travelled to a facility that was not their closest public facility. The average excess travel of these patients was 26.8km, with the median excess travel being 13.6km. Additionally, of patients who received care in a public facility, 47.4% travelled past a closer private facility. The average excess travel distance of these patients was 23.1km and the median excess travel was 11.5km. In the case of patients who received radiotherapy at a private facility, 92.8% travelled to a clinic that was not their closest. The average excess of these patients was 36.6km with a median excess travel distance of 15.6km. Access to radiotherapy facilities remains unequal in Victoria with some patients having to travel significantly greater distances than average. This significant travel may require patients to take time off work or live away from home presenting additional financial challenges. The reasons for the large travel distances and any excess travel have not yet been identified but will be the subject of further study.

Design and Analysis of XY Large Travel Micro Stage Based on Secondary Symmetric Lever Amplification.

This study presents a newly developed piezoelectric drive mechanism for the purpose of designing, analyzing, and testing a micro-positioning platform driven by piezoelectric actuators. The platform incorporates a piezoelectric ceramic actuator and a flexible hinge drive and features a symmetrical two-stage lever (STSL) amplification mechanism and a parallelogram output structure. The implementation of this design has led to notable enhancements in the dynamic properties of the platform, thereby eliminating the undesired parasitic displacement of the mechanism. An analytical model describing the fully elastic deformation of the platform is established, which is further verified by finite element simulation. Finally, the static and dynamic performances of the platform are comprehensively evaluated through experiments. A closed-loop control strategy is adopted to eliminate the nonlinear hysteresis phenomenon of the piezoceramic actuator (PEA). The experimental results show that the piezoelectric micro-actuator platform has a motion range of 97.84 μm × 98.03 μm; the output coupling displacement error is less than 1%; the resolutions of the two axes are 8.1 nm and 8 nm, respectively; and the x-axis and y-axis trajectory tracking errors are both 0.6%. The piezoelectric micromotion platform has good dynamic properties, precision, and stability. The design has a wide application potential in the field of micro-positioning.

Exploring Melbourne Metro Train Passengers’ Pre-Boarding Behaviors and Perceptions

The focus on sustainable transportation has increased interest in promoting sustainable modes of transport, such as rail. Understanding train passengers’ behaviors and perceptions is essential to enhance their travel experience and increase train ridership. Pre-boarding behaviors and perceptions are crucial in shaping the overall train travel experience. However, there are limited studies that have developed a systematic framework for investigating train passengers’ pre-boarding behaviors and perceptions. This paper examines the train passenger’s pre-boarding behaviors and perceptions about the station and platform. The study adopts a mixed-methods approach by developing a pre-boarding decision framework and combining it with questionnaire surveys to explore passengers’ behaviors and perceptions on the platform before boarding. A total of 429 valid responses from Melbourne metro train users were used for analysis. Descriptive statistics and correlation techniques were applied to identify patterns and relationships. The findings reveal common pre-boarding behaviors and perceptions. Furthermore, the study uncovers factors influencing these behaviors and perceptions, such as passenger demographics, travel patterns, and specific trip characteristics. For example, carrying large items and travel frequency significantly impact passengers’ travel experience in the pre-boarding phase. Waiting time, group travel, carrying small items, gender, and age group also significantly impact some pre-boarding behavior variables. Travel time, on the other hand, makes no significant impact on any of the pre-boarding variables that we examined. This research provides valuable insights for rail service operators and policymakers to enhance the pre-boarding experience, optimize station design, and improve passenger satisfaction.

Integral back-stepping active disturbance rejection control for piezoelectric stick-slip drive nanopositioning stage

Piezoelectric stick-slip driven nanopositioning stage (PSSNS) with nanometer resolution has been widely used in the field of micro-operation. However, it is difficult to achieve nanopositioning over large travel, and its positioning accuracy is affected by the hysteresis characteristics of the piezoelectric elements, external uncertain disturbances, and other nonlinear factors. To overcome the above-mentioned problems, a composite control strategy combining stepping mode and scanning mode is proposed in this paper, and an integral back-stepping linear active disturbance rejection control (IB-LADRC) strategy is proposed in the scanning mode control phase. First, the transfer function model of the system in the micromotion part was established, and then the unmodeled part of the system and the external disturbance were treated as the total disturbance and extended to a new system state variable. Second, a linear extended state observer was used as the core of the active disturbance rejection technique to estimate displacement, velocity, and total disturbance in real time. In addition, by introducing virtual control variables, a new control law was designed to replace the original linear control law and improve the positioning accuracy and robustness of the system. Furthermore, the effectiveness of the IB-LADRC algorithm was verified by simulation comparison experiments and experimentally validated on a PSSNS. Finally, experimental results show that the IB-LADRC is a practical solution for a controller capable of handling disturbances during the positioning of a PSSNS with a positioning accuracy of less than 20 nm, which essentially remains constant under load.

A novel two-stage approach for energy-efficient timetabling for an urban rail transit network

Urban rail transit (URT) is the backbone transport mode in metropolitan areas to accommodate large travel demands. The high energy consumption of URT becomes a hotspot problem due to the ever-increasing operation mileages and pressing agendas of carbon neutralization. The high model complexity and inconsistency in the objectives of minimizing passenger travel time and operational energy consumption are the main challenges for energy-efficient timetabling for a URT network with multiple interlinked lines. This study proposes a general model framework of timetabling and passenger path choice in a URT network to minimize energy consumption under passenger travel time constraints. To obtain satisfactory energy-efficient nonuniform timetables, we suggest a novel model reformulation as a tree knapsack problem to determine train running times by a pseudo-polynomial dynamic programming algorithm in the first stage. Furthermore, a heuristic sequencing method is developed to determine nonuniform headways and dwell times in the second stage. The suggested model framework and solution algorithm are tested using a real-world URT network, and the results show that energy consumption can be considerably reduced given certain travel time increments.

Small coral reef fishes with large ecological footprints

Seascape connectivity can facilitate key ecosystem functions in complex ecosystems like coral reefs. Many reef fishes move across the seascape, bridging different ecosystems. However, their role in shaping important functions, such as biomass production and nutrient cycling, is still poorly understood. This study, therefore, assesses the extent of natural movements of cardinalfishes (Apogonidae), one of the major contributors to nocturnal fish biomass production with the potential for a major role in transferring energy and nutrients between sandy ecosystems and adjacent coral reefs. Consistent with previous work, showing their ability to move distances of 100 s to 1000 s of metres when displaced, we reveal that these small fishes undergo major voluntary nocturnal foraging forays extending up to at least 145 m from reef structures. Their estimated daily movement distances are at least 430 times greater than expected based solely on body size-home range expectations. Given their large travel distances and strong homing abilities, apogonids may provide a major conduit for material transfer between lagoonal soft sediment habitats and adjacent coral reefs. These results highlight the potential importance of apogonids in the cross-system or cross-habitat transport of energy and nutrients on coral reefs.