Search

Eleven phase change materials (PCMs) for cooling humans in heat-stressed conditions were evaluated for their cooling characteristics. Effects of packaging material and segmentation were also investigated. Sample packs with a different type PCM (water- and oil-based PCMs, cooling gels, inorganic salts) or different packaging (aluminum, TPU, TPU + neoprene) were investigated on a hotplate. Cooling capacity, duration, and power were determined. Secondly, a PCM pack with hexagon compartments was compared to an unsegmented version with similar content. Cooling power decreased whereas cooling duration increased with increasing melting temperature. The water-based PCMs showed a >2x higher cooling power than other PCMs, but were relatively short-lived. The flexible gels and salts did not demonstrate a phase change plateau in cooling power, compromising their cooling potential. Using a TPU or aluminum packaging was indifferent. Adding neoprene considerably extended cooling duration, while decreasing power. Segmentation has practical benefits, but substantially lowered contact area and therefore cooling power.

There are different thermal perception models linked to a mathematical thermophysiological human model, with which the thermal sensation under stationary and/or dynamic conditions can be evaluated. Each of these perception and thermophysiological models have their own field of application. Stolwijk developed a thermophysiological human model without an associated thermal perception model, which today is still the basis for other mathematical thermophysiological models. Fiala developed the FPC model, also based on the Stolwijk model, and is one of the latest developments in the field of thermophysiological human models. In the FPC model, an equation is included with which the thermal sensation under stationary and dynamic conditions can be assessed; the so-called Dynamic Thermal Sensation (DTS). The DTS equation is, however, specifically developed for use in combination with the FPC model. In contrast to the Stolwijk model, the source code of the computer programs of the later developed thermophysiological human models is not freely available, which limits the use and applicability of the models in practice. It is precise because of the availability of the source code that the Stolwijk model is still used in industry and the research world. The question, therefore, arises: ‘To what extent can a human transient thermal sensation equation be derived, combined with the Stolwijk model, in a similar way to that used for the DTS equation in the FPC model?’.

Contains fulltext : 238809.pdf (Publisher’s version ) (Open Access) The environmental conditions during the Tokyo Olympic and Paralympic Games are expected to be challenging, which increases the risk for participating athletes to develop heat-related illnesses and experience performance loss. To allow safe and optimal exercise performance of Dutch elite athletes, the Thermo Tokyo study aimed to determine thermoregulatory responses and performance loss among elite athletes during exercise in the heat, and to identify personal, sports-related, and environmental factors that contribute to the magnitude of these outcomes. For this purpose, Dutch Olympic and Paralympic athletes performed two personalized incremental exercise tests in simulated control (15°C, relative humidity (RH) 50%) and Tokyo (32°C, RH 75%) conditions, during which exercise performance and (thermo)physiological parameters were obtained. Thereafter, athletes were invited for an additional visit to conduct anthropometric, dual-energy X-ray absorptiometry (DXA), and 3D scan measurements. Collected data also served as input for a thermophysiological computer simulation model to estimate the impact of a wider range of environmental conditions on thermoregulatory responses. Findings of this study can be used to inform elite athletes and their coaches on how heat impacts their individual (thermo)physiological responses and, based on these data, advise which personalized countermeasures (i.e. heat acclimation, cooling interventions, rehydration plan) can be taken to allow safe and maximal performance in the challenging environmental conditions of the Tokyo 2020 Olympic and Paralympic Games.

We propose an approach to designing smart wearables that act as partners to help people cope with stress in daily life. Our approach contributes to the developing field of smart wearables by addressing how technological capabilities can be designed to establish partnerships that consider the person, the situation, and the appropriate type of support. As such, this study also contributes to healthcare by opening up novel technology-supported routes to stress treatment and care. We present the results of a phenomenological study conducted with three war veterans who suffer from chronic posttraumatic stress disorder. We describe how their experiences of dealing with their stress informed our design approach, and discuss the implications of these results on smart wearables and stress management in general. We conclude by reflecting on the limitations of this study and directions for future work.

Current athlete monitoring practice in team sports is mainly based on positional data measured by global positioning or local positioning systems. The disadvantage of these measurement systems is that they do not register lower extremity kinematics, which could be a useful measure for identifying injury-risk factors. Rapid development in sensor technology may overcome the limitations of the current measurement systems. With inertial measurement units (IMUs) securely fixed to body segments, sensor fusion algorithms and a biomechanical model, joint kinematics could be estimated. The main purpose of this article is to demonstrate a sensor setup for estimating hip and knee joint kinematics of team sport athletes in the field. Five male subjects (age 22.5 +/- 2.1 years; body mass 77.0 +/- 3.8 kg; height 184.3 +/- 5.2 cm; training experience 15.3 +/- 4.8 years) performed a maximal 30-meter linear sprint. Hip and knee joint angles and angular velocities were obtained by five IMUs placed on the pelvis, both thighs and both shanks. Hip angles ranged from 195 degrees (+/- 8 degrees) extension to 100.5 degrees (+/- 8 degrees) flexion and knee angles ranged from 168.6 degrees (+/- 12 degrees) minimal flexion and 62.8 degrees (+/- 12 degrees) maximal flexion. Furthermore, hip angular velocity ranged between 802.6 degrees.s(-1) (+/- 192 degrees.s(-1)) and -674.9 degrees.s(-1) (+/- 130 degrees.s(-1)). Knee angular velocity ranged between 1155.9 degrees.s(-1) (+/- 200 degrees.s(-1)) and -1208.2 degrees.s(-1) (+/- 264 degrees.s(-1)). The sensor setup has been validated and could provide additional information with regard to athlete monitoring in the field. This may help professionals in a daily sports setting to evaluate their training programs, aiming to reduce injury and optimize performance.

This paper presents experimental testing of a new semi-active vibration control device comprising a shape memory polymer (SMP) core that is reinforced by an SMP-aramid composite skin. This control device works as a load-transfer component that can be integrated into truss and frame structures in the form of a joint. At the material level, thermal actuation from ambient (25 degrees C) to transition temperature (65 degrees C) causes a significant 40fold increase in damping due to viscoelastic effects. At the component level, uniaxial tensile and four-point bending tests have shown that tensile strength depends primarily on the bond strength between the reinforcement skin and the structural element while flexural strength depends on the strength of the reinforcement skin fibers. Through cyclic testing, it has been observed that material viscoelasticity is beneficial to ductility and energy dissipation. When the joint core is actuated to the SMP transition temperature, axial and flexural stiffness decrease by up to 50% and 90%, respectively. The property change at material and component levels enable tuning the frequency and damping ratio at the structure level, which has been successfully employed to mitigate the dynamic response of a 1/10 scale three-story prototype frame under resonance and earthquake loadings.

ObjectivesTo evaluate how separate and combined climatic parameters affect peak core temperature during exercise in the heat using computer simulations fed with individual data.MethodsThe impact of eight environmental conditions on rectal temperature (Tre) was determined for exercise under heat stress using the Fiala-thermal-Physiology-and-Comfort simulation model. Variations in ambient temperature (Ta±6°C), relative humidity (RH±15%) and solar radiation (SR+921 W/m2) were assessed in isolation and combination (worst-case/best-case scenarios) and compared with baseline (Ta32°C, RH 75%, SR 0 W/m2). The simulation model was fed with personal, anthropometric and individual exercise characteristics.Results54 athletes exercised for 46±10 min at baseline conditions and achieved a peak core temperature of 38.9±0.5°C. Simulations at a higher Ta (38°C) and SR (921 W/m2) resulted in a higher peak Tre compared with baseline (+0.6±0.3°C and +0.5±0.2°C, respectively), whereas a higher RH (90%) hardly affected peak Tre (+0.1±0.1°C). A lower Ta (26°C) and RH (60%) reduced peak Tre by −0.4±0.2°C and a minor −0.1±0.1°C, respectively. The worst-case simulation yielded a 1.5±0.4°C higher Tre than baseline and 2.0±0.7°C higher than the best-case condition.ConclusionCombined unfavourable climatic conditions produce a greater increase in peak core temperature than the sum of its parts in elite athletes exercising in the heat.

Sweat sensors allow for new unobtrusive ways to continuously monitor an athlete's performance and health status. Significant advances have been made in the optimization of sensitivity, selectivity, and durability of electrochemical sweat sensors. However, comparing the in situ performance of these sensors in detail remains challenging because standardized sweat measurement methods to validate sweat sensors in a physiological setting do not yet exist. Current collection methods, such as the absorbent patch technique, are prone to contamination and are labor-intensive, which limits the number of samples that can be collected over time for offline reference measurements. We present an easy-to-fabricate sweat collection system that allows for continuous electrochemical monitoring, as well as chronological sampling of sweat for offline analysis. The patch consists of an analysis chamber hosting a conductivity sensor and a sequence of 5 to 10 reservoirs that contain level indicators that monitor the filling speed. After testing the performance of the patch in the laboratory, elaborate physiological validation experiments (3 patch locations, 6 participants) were executed. The continuous sweat conductivity measurements were compared with laboratory [Na+] and [Cl-] measurements of the samples, and a strong linear relationship (R2 = 0.97) was found. Furthermore, sweat rate derived from ventilated capsule measurement at the three locations was compared with patch filling speed and continuous conductivity readings. As expected from the literature, sweat conductivity was linearly related to sweat rate as well. In short, a successfully validated sweat collection patch is presented that enables sensor developers to systematically validate novel sweat sensors in a physiological setting.

The environmental conditions during the Tokyo Olympic and Paralympic Games are expected to be challenging, which increases the risk for participating athletes to develop heat-related illnesses and experience performance loss. To allow safe and optimal exercise performance of Dutch elite athletes, the Thermo Tokyo study aimed to determine thermoregulatory responses and performance loss among elite athletes during exercise in the heat, and to identify personal, sports-related, and environmental factors that contribute to the magnitude of these outcomes. For this purpose, Dutch Olympic and Paralympic athletes performed two personalized incremental exercise tests in simulated control (15°C, relative humidity (RH) 50%) and Tokyo (32°C, RH 75%) conditions, during which exercise performance and (thermo)physiological parameters were obtained. Thereafter, athletes were invited for an additional visit to conduct anthropometric, dual-energy X-ray absorptiometry (DXA), and 3D scan measurements. Collected data also served as input for a thermophysiological computer simulation model to estimate the impact of a wider range of environmental conditions on thermoregulatory responses. Findings of this study can be used to inform elite athletes and their coaches on how heat impacts their individual (thermo)physiological responses and, based on these data, advise which personalized countermeasures (i.e. heat acclimation, cooling interventions, rehydration plan) can be taken to allow safe and maximal performance in the challenging environmental conditions of the Tokyo 2020 Olympic and Paralympic Games.

Shape-shifting materials are a powerful tool for the fabrication of reconfigurable materials. Upon activation, not only a change in their shape but also a large shift in their material properties can be realized. As compared with the 4D printing of 2D-to-3D shape-shifting materials, the 4D printing of reconfigurable (i.e., 3D-to-3D shape-shifting) materials remains challenging. That is caused by the intrinsically 2D nature of the layer-by-layer manner of fabrication, which limits the possible shape-shifting modes of 4D printed reconfigurable materials. Here, we present a single-step production method for the fabrication and programming of 3D-to-3D shape-changing materials, which requires nothing more than a simple modification of widely available fused deposition modeling (FDM) printers. This simple modification allows the printer to print on curved surfaces. We demonstrate how this modified printer can be combined with various design strategies to achieve high levels of complexity and versatility in the 3D-to-3D shape-shifting behavior of our reconfigurable materials and devices. We showcase the potential of the proposed approach for the fabrication of deployable medical devices including deployable bifurcation stents that are otherwise extremely challenging to create. Shape-shifting structures are important building blocks in the design of reconfigurable materials and devices with advanced functionalities. Here, versatile metamaterials with 3D-to-3D shape-shifting behavior upon thermal activation are fabricated by adapting a 3D printer to print on curved surfaces.

An innovative deicing system for aircraft leading edges has been developed which integrates heater elements into fibre metal laminates. Such an electrical system can lead to weight reductions and more efficient performances compared to conventional bleed air systems. However, the combination of thermal and mechanical loadings also raises new questions on the durability of such a structure, in particular due to the repeated heating to elevated temperature. The linear viscoelastic creep behaviour, including the effects of temperature and ageing, is therefore investigated for manufactured FM906 glass-fibre epoxy composite as used in heated GLARE. A master curve is derived based on the time–temperature and time–age superposition. The effect of physical ageing during loading is included in a long-term creep prediction.