External Temperature Variations Research Articles

Finite element modeling of active cracking in actively reinforced concrete pavement slab exposed to fluctuating temperature

The continuously reinforced concrete pavement (CRCP) system grapples with challenges such as non-uniform transverse crack patterns and the need for substantial reinforcement. Field research on the Belgian CRCP sections along motorway E313 indicates that active cracking induced by partial surface saw-cuts consistently leads to transverse crack patterns. This study introduces an innovative modification to the CRCP: the actively reinforced concrete pavement design (ARCP). The ARCP leverages partial surface saw-cuts to reduce reinforcement needs by replacing continuous-length steel bars with partial-length counterparts. The main objective of the present study is to develop a 3D finite element (FE) model capturing the active cracking behavior of ARCP under realistic external temperature variations. Comparative analysis with CRCP considers early-age crack patterns, crack strain development, and the distribution of maximum steel stress for different steel ratios (0.67%, 0.75%, and 0.85%). FE simulation results align with field data, indicating that ARCP exhibits similar early-age cracking behavior to CRCP but with a significant 24 to 42% reduction in total reinforcement. This innovation presents a promising avenue for addressing CRCP challenges while optimizing material usage in pavement construction.

Effect of Using a Solar Can Heater Collector on the Temperature of a Room at Several External Temperature Variations

Effect of Using a Solar Can Heater Collector on the Temperature of a Room at Several External Temperature Variations

Optimization of power feedback control system for HCN interferometer on EAST Tokamak

The Hydrogen Cyanide (HCN) interferometer stands as an indispensable diagnostic tool, designated to measure the line-integrated electron density on the Experimental Advanced Superconducting Tokamak (EAST), thereby offering essential density feedback signals for EAST operation. The HCN laser used in the interferometer is a continuous glow discharge gas laser. However, owing to variations in external ambient temperature, the HCN laser exhibits output power instability. The current power automatic feedback control system for the HCN laser interferometer exhibits low actuator adjustment precision, thereby limiting its ability to achieve maximum output power. Moreover, the system may cause a temporary power drop to zero during adjustment, while EAST operation requires the HCN laser interferometer to maintain high power continuously. In order to solve the issues, this paper developed an innovative actuator that ingeniously amalgamates the virtues of piezoelectric ceramic and stepper motor. This novel actuator, demonstrating a broad adjustment range and high precision, is intended to replace the present one in the HCN interferometer power control system. While the stepper motor executes coarse adjustment, the piezoelectric ceramic enables precise adjustment, thus enhancing the adjustment accuracy of the automatic power control system to a sub-micrometer level and an adjustment range greater than 5 mm. Accurate determination of the regulator's adjustment direction can significantly improve the efficiency of adjustment. The slope of the laser output power peak decreases as it approaches the maximum value, and increases as it moves away from the maximum value. Therefore, this system replaces the original threshold algorithm with a slope algorithm. By correctly judging the adjustment direction, the efficiency of adjustment is improved. Furthermore, this algorithm can keep the output power stable on a power peak. There will be no instances of zero power output during the adjustment, allowing the power to remain stable above the set threshold for a long time. Currently, this system has been successfully applied to the HCN interferometer, and testing has found that the system can maintain stability for at least 16 hours. Furthermore, even when the laser output power was intentionally reduced to below the set threshold, the system was able to respond quickly and adjust the output, rapidly restoring it to above the predefined threshold. Multiple tests have shown the strong robustness of the system, indicating it meets the stringent demands of the EAST's complex environment.

Multistable Metafluid based Energy Harvesting and Storage.

The thermodynamic properties of fluids play a crucial role in many engineering applications, particularly in the context of energy. Fluids with multistable thermodynamic properties may offer new paths for harvesting and storing energy via transitions between equilibria states. Such artificial multistable fluids can be created using the approach employed in metamaterials, which controls macro-properties through micro-structure composition. In this work, the dynamics of such "metafluids" is examined for a configuration of calorically-perfect compressible gas contained within multistable elastic capsules flowing in a fluid-filled tube. The velocity-, pressure-, and temperature-fields of multistable compressible metafluids is studied by both analytically and experimentally, focusing on transitions between different equilibria. The dynamics of a single capsule is first examine, which may move or change equilibrium state, due to fluidic forces. The interaction and motion of multiple capsules within a fluid-filled tube is then studied. It shows that such a system can be used to harvest energy from external temperature variations in either time or space. Thus, fluidic multistability allows specific quanta of energy to be captured and stored indefinitely as well as transported as a fluid, via tubes, at standard atmospheric conditions without the need for thermalisolation.

Thermal performance analysis of PCM solar wall under variable natural conditions: An experimental study

Low-carbon technologies are critical for mitigating climate change and achieving net-zero emission buildings. Phase change material (PCM) solar wall as a low-carbon technology is a passive heating/cooling system with the potential to cover a significant portion of building energy demand. To better understand the potential of PCM solar walls in different climates, further research into their performance is needed. This research is based on an experimental investigation of the performance of the Solar wall test cell in changing natural conditions for cold and warm seasons. A series of experiments were conducted in both seasons by recording the variation of exterior and interior temperature, as well as solar radiation. Statistical tools were used to analyze the influence of variations in external air temperature and solar radiation on the thermal characteristics of the solar wall in the cell. The results showed a significant difference between external and internal temperature variations for both seasons. Particularly, the wall had the potential during the heating season to maintain the temperature of the test cell above 20 °C for up to 7 h, while in the cooling season, it is observed that the wall keeps room temperature for about 17 h within the comfort range.

Ferroelectric topologically configurable multilevel logic unit

Multilevel devices demonstrating switchable polarization enable us to efficiently realize neuromorphic functionalities including synaptic plasticity and neuronal activity. Here we propose using the ferroelectric logic unit comprising multiple nanodots disposed between two electrodes and coated by the dielectric material. We devise the integration of the ferroelectric logic unit, providing topologically configurable non-binary logic into a gate stack of the field-effect transistor as an analog-like device with resistive states. By controlling the charge of the gate, we demonstrate the various routes of the topological switchings between different polarization configurations in ferroelectric nanodots. Switching routes between different logic levels are characterized by hysteresis loops with multiple branches realizing specific interconnectivity regimes. The switching between different types of hysteresis loops is achieved by the variation of external fields and temperature. The devised ferroelectric multilevel devices provide a pathway toward the novel topologically-controlled implementation of discrete synaptic states in neuromorphic computing.

Temperature Tunable 4D Polymeric Photonic Crystals

AbstractPhotonic crystals owe their multitude of optical properties to the way their structure creates interference effects. It is therefore possible to influence the photonic response by acting on their physical structure. In this article, tunable photonic crystals made by elastic polymers that respond to their environment are explored, in particular with a physical deformation under temperature variation. This creates a feedback process in which the photonic response depends on its physical structure, which itself is influenced by the environmental changes. By using a multi‐photon polymerization process specifically optimized for soft responsive polymers such as Liquid Crystalline Networks, highly resolved, reproducible, and mechanically self‐standing photonic crystals are fabricated. The physical structure of the 3D woodpile can be tuned by an external temperature variation creating a reversible spectral tuning of 50 nm in the telecom wavelength range. By comparing these results with finite element calculations and temperature induced shape‐change, it is confirmed that the observed tuning is due to an elastic deformation of the structure. The achieved nanometric patterning of tunable anisotropic photonic materials will further foster the development of reconfigurable photonic crystals with point defects acting as tunable resonant cavities and, more in general, of 4D nanostructures.

Fabrication and Sensing Characteristics of Long-Period Fiber Grating in Capillary Fiber

We propose a novel fiber device based on arc-induced long-period fiber gratings (LPFGs) in a hollow core silica capillary. This device is made up of a lead-in single-mode fiber (SMF), LPFGs in capillary (CLPFGs), and a lead-out SMF, with a tapered air cavity (TAC) connecting SMF and capillary. The transmissive characteristics of capillary with and without LPFGs are analyzed theoretically and experimentally. Mode coupling of CLPFGs at longer wavelength could be enhanced, as well as the sensing performance increases times over the capillary without gratings. The refractive index (RI) sensitivity can reach to be 15 713.5 nm/RIU in the RI range from 1.451 to 1.456. Moreover, with the asymmetric index distribution induced in the capillary, the CLPFGs present vector bending properties that the bending sensitivities are 79.4 and −8.8 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{1}}$ </tex-math></inline-formula> , for bending directions at 0° and 180°, respectively. Furthermore, the proposed device shows negligible change to the external temperature variation, which could solve the cross-sensitivity problem. With the advantages of compactness, low cost, and ease of fabrication, the proposed device is potential in high-sensitivity RI sensing fields and vector bending measurement.

Development of a Core Body Thermometer Applicable for High-Temperature Environment Based on the Zero-Heat-Flux Method.

Monitoring core body temperature (CBT) allows observation of heat stress and thermal comfort in various environments. By introducing a Peltier element, we improved the zero-heat-flux core body thermometer for hot environments. In this study, we performed a theoretical analysis, designed a prototype probe, and evaluated its performance through simulator experiments with human subjects. The finite element analysis shows that our design can reduce the influence of external temperature variations by as much as 1%. In the simulator experiment, the prototype probe could measure deep temperatures within an error of less than 0.1 °C, regardless of outside temperature change. In the ergometer experiment with four subjects, the average difference between the prototype probe and a commercial zero-heat-flux probe was +0.1 °C, with a 95% LOA of -0.23 °C to +0.21 °C. In the dome sauna test, the results measured in six of the seven subjects exhibited the same trend as the reference temperature. These results show that the newly developed probe with the Peltier module can measure CBT accurately, even when the ambient temperature is higher than CBT up to 42 °C.

Robustness of an Economic Nonlinear Model Predictive Control for Wind Turbines Under Changing Environmental and Wear Conditions

In this letter, the authors have assessed the robustness of an Economic Nonlinear Model-Predictive Controller (ENMPC) aimed at maximizing the power production of wind turbines. The scope of this letter is to quantify the sensitivity of this type of controller concerning wind conditions, climate, wind speed prediction unavailability, and aerodynamic performance degradation. A power production controller’s robustness is crucial for the wind turbine industry due to the extreme variability of external conditions and the wear caused by long-term continuous operativity. Model-Predictive controllers are, in principle, more prone to robustness issues concerning standard controllers, a fact that limits their adoption on actual wind turbines. The analysis is performed with the fully-aeroelastic solver OpenFAST considering a wide set of realistic load cases. It is demonstrated that the ENMPC previously developed is robust to wind prediction unavailability and change in wind turbulence intensity. Conversely, it is not robust to the modelling error due to aerodynamic degradation. Indeed, a reduction in generated power concerning the reference controller is observed, especially for operating region two and end-life blades. Finally, a significant increase in power production is achieved considering the external temperature variation thanks to the ENMPC’s direct handling of the generator temperature constraint.

Influence of root fragility and irrigation on external root temperature variation during preparation for fiberglass posts

Influence of root fragility and irrigation on external root temperature variation during preparation for fiberglass posts

Capillary based hybrid fiber sensor in a balloon-like shape for simultaneous measurement of displacement and temperature

In this work, a hybrid sensor based on a silica capillary in a balloon-like shape for simultaneous measurement of displacement and temperature is proposed for the first time, to the best of our knowledge. The sensor is fabricated by splicing a segment of a hollow core fiber between two single mode fibers (SMF) and by bending the fiber in a balloon shape with the capillary at the top-center position. In a transmission scheme, the SMF-capillary-SMF configuration excites an antiresonant (AR) guidance and the balloon shape enhances a Mach-Zehnder interferometer (MZI). The different responses of the interferometers to external displacement and temperature variations are conducive to a hybrid application of the sensor for simultaneous measurement of these parameters. Experimental results show that, for a capillary length of 1.2 cm and a balloon length of 4 cm, AR is insensitive to displacement and its sensitivity to temperature is 14.3 pm/°C, while the MZI has a sensitivity to displacement of 1.68 nm/mm and twice the sensitivity of AR to temperature, of 28.6 pm/°C. The proposed fiber sensor consists of only one sensing element in one configuration exciting two interferometers at the same time, which makes it of simple fabrication as well as low cost.

Preparation and characterization of structurally variable inorganic nanofibrous mats with large surface area for intelligent temperature regulation textiles

Hierarchical structure and large specific surface area are vital for the substrate materials of form-stable phase change materials (FSPCMs) incoporated within intelligent temperature reulation textiles. Microemulsion electrospinning is an efficient method to prepare hierarchically porous substrate materials. Herein, structurally variable TiO2/SiO2/C (TSC) nanofibers were fabricated via microemulsion electrospinning followed by calcination as the substrate materials of FSPCMs. The interior structure, specific surface area, thermal energy storage and thermal regulation properties of TSC nanofibrous mats were characterized in detail. Interestingly, the intrinsic structure of nanofibers could be tuned by varying the composition of precursor solution. The minimum specific surface area of TiO2/SiO2/C nanofibrous mats was as high as 685.52 m2·g−1. The melting and crystallization enthalpy of TiO2/SiO2/C nanofibrous mats-based FSPCMs were more than 126.91 and 120.36 J·g−1, respectively. Furthermore, the manufactured FSPCMs were applied as the middle layer of temperature regulation textiles with a sandwich structure, the largest temperature difference between temperature regulation textiles and conventional textiles was up to 12.6 °C, indicating the manufactured temperature regulation textiles could effectively buffer the external temperature variation. The results proved microemulsion electrospinning is indeed an efficient method to prepare desired substrate materials of FSPCMs.

Temperature-triggered smart milk-derived hydrogel with programmable adhesion for versatile skin-attached iontronics

Despite the current advances in adhesives, it is still a huge challenge to develop a programmable adhesion material for wearable and skin-attached devices. Herein, a skin temperature-triggered smart adhesive hydrogel is developed by one-sidedly infiltrating polyvalent metal ions into the UCST-typed thermosensitive copolymers comprising milk-derived sodium caseinate (SC). The resulting hydrogel presents asymmetric and tunable adhesion, which is capable of the repeated, on-demand detachments by a mild skin temperature trigger. Meanwhile, the hydrogel also shows the programmable turbidity-switching ability because of adjustable phase transformation, and outstanding antimicrobial properties (killing rate: >99.0%). Besides, the hydrogel can sensitively perceive external strain (GF: 37.59, response time: 169 ms) and temperature (TCR: –4.03%/℃) variation by electrical signals. Thanks to these excellent features, the hydrogel can be applied to versatile wearable iontronics to precisely monitor various human motions, physiological signals and thermal distributions in real time. Therefore, our study establishes a novel and effective route for the rational design and fabrication of intelligent skin-attached materials.

Fabrication of 5D Fresnel Lenses via Additive Manufacturing.

The consistent developments in additive manufacturing (AM) processes are revolutionizing the fabrication of 3-dimensional (3D) parts. Indeed, 3D printing processes are prompt, parallel, material efficient, and cost-effective, along with their capabilities to introduce added dimensions to the computer-aided design (CAD) models. Notably, 3D Printing is making progressive developments to fabricate optical devices such as regular lenses, contact lenses, waveguides, and more recently, Fresnel lenses. But extended functionalities of these optical devices are also desirable. Therefore, we demonstrate masked stereolithography (MSLA) based fabrication of five-dimensional (5D) Fresnel lenses by incorporating color-change phenomena (4th dimension) using thermochromic powder that changes color in response to external temperature variations (25-36 °C). The holographic diffraction effect (5th dimension) is produced by imprinting a diffraction grating during the printing process. Optical focusing performance for the 5D printed lenses has been evaluated by reporting achievable focal length, with <2 mm average deviation, without postprocessing in 450-650 nm spectral range. However, in the near IR region (850-980 nm), the average deviation was around 11.5 mm. Enhanced optical properties along with surface quality have been reported. Thus, MSLA process can fabricate optical components with promising applications in the fields of sensing and communication.

Understanding the effects of altering impact velocities and temperatures on basalt textile: An experiment approach

Basalt textiles are finding new applications in several industries due to less complicated composition, high elastic modulus and remarkable tenacity. Present study examines the low-velocity impact (LVI) performance of basalt textile at four distinct incidence velocities: 1, 2, 3, and 4 m/s. The effect of changing external temperatures, particularly −50, 0, 25, and 100 °C, are also investigated. To evaluate the low-velocity impact response, two types of surface coated basalt textiles were tested (i) single-layer basalt textile or SLBT and (ii) double-layered basalt textile or DLBT. Different parameters such as first-crack load, deflection at first-crack, peak impact load, ultimate deflection, energy absorbed at peak load, total energy absorption are considered and compared. The temperature influence factor (TIF) was measured and compared with the reference sample at room temperature to assess the influence of external temperature variations on SLBT. The cumulative failure probability of textile under LVI at varied loads and temperatures revealed a substantial variation in mechanical performance. The failure patterns and microscopic morphologies of fractured textiles demonstrated that two layers of textiles give superior damage resistance under LVI condition.

End-to-end learning of self-rectification and self-supervised disparity prediction for stereo vision

Stereo rectification and stereo matching are two critical components for the practical application of stereo vision systems. Previous studies treat them as two individual issues. For stereo rectification, various traditional algorithms are proposed to estimate homography transformations, but the performance and the efficiency are unsatisfactory for real-time deployment. For stereo matching, disparity accuracy has been largely improved by learning based methods. However, the input data of all previous stereo networks are assumed to be a pair of offline pre-rectified images, making them invalidate for accurate matching when the stereo vision system suffers from mechanical misalignment due to external collisions or temperature variations. In this paper, we optimize these two components jointly and propose an end-to-end learning framework to achieve online self-rectification and self-supervised disparity prediction simultaneously. The overall network contains two cascaded subnetworks which enable stereo rectification and stereo matching sequentially for a pair of unrectified images. The experimental results are evaluated on both publicly available datasets and realistic scenarios. Evaluation results demonstrate that, the proposed network produces state-of-the-art results for self-rectification in terms of computation accuracy and speed, and also produces competitive disparity results with previous self-supervised methods. Therefore, the proposed design provides a more practical and efficient solution for stereo vision systems deployed on mobile platforms.

Establishment and optimization of temperature compensation model for benzoic acid detection based on terahertz metamaterial

To regulate the use of food additives is of great significance to human health, for the excessive use of food additives can cause damage to human body so serious as organ failure and even cancers. Benzoic acid (BA) is a widely used food preservative, and it is of great importance to achieve high-sensitive detection of it. Conventional THz detection method can obtain the fingerprint spectrum of the sample in the terahertz band, it can only detect a sample to be detected at a milligram level, and it is not suitable for the micro or trace analysis of the sample. In this paper, an enhanced terahertz (THz) micro-nano structure of metamaterial based on electromagnetic theory was designed to achieve enhanced detection of benzoic acid additives by THz technology. THz spectroscopy is more sensitive to temperature changes than other spectroscopic detection techniques, so it is particularly important to find out a method of spectral temperature compensation to minimize the inference caused by temperature variations in the detection of samples with variable temperature. To this end, based on the enhanced technology of THz metamaterial, an optimized compensation method for external temperature variations was explored in this paper. Firstly, the THz spectra of seven samples with different concentrations under six different temperatures were collected. Secondly, smoothing and baseline correction methods were used to preprocess the spectra to study the better spectral pretreatment methods. To reduce the influence of the change of external temperature on the detection, the External Parameter Orthogonalization (EPO) and Generalized Least Squares Weighting (GLSW) methods were introduced to compensate the temperature change. These two aforementioned methods were compared with the method without temperature compensation, respectively. Then, Uninformative Variable Elimination (UVE), principal component analysis (PCA),successive projections algorithm (SPA) and Competitive Adaptive Reweighted Sampling (CARS) were used to explore the optimal terahertz band selection method. Finally, Partial Least Squares (PLS) and Least square support vector machine (LS-SVM) models were established, respectively, to realize the enhanced detection of benzoic acid additives. The LS-SVM model combined with SPA and GLSW has the best effect, with the Rp2 of 0.9892, the RMSEP of 3.8412 × 10−5 and the LOD of 1.158 × 10−4 g/mL. The LOD of the model is nearly three times higher than that of the mixed global model. The results show that the GLSW method exhibited a better compensation effect on the THz spectra of benzoic acid solution samples at different temperatures. Therefore, this study can be applied to other temperature-compensated models and can also provide reference for the detection of samples with variable temperature.

Radio frequency over fiber technology for SKA-low receiver

The signal reception chain is an essential element for achieving the square kilometer array-low (SKA-low) system requirements in terms of high sensitivity and dynamic range. The balance between gain, linearity, and low power consumption, as well as the cost, are fundamental parameters that influence the selection of the most suitable technology for SKA-low. Further factors, such as low self-generated radio frequency (RF) interference, high reliability, robustness under extreme environment, and last but not least, the distance between the antennas and the acquisition systems, have impacts on the selection for both architecture and receiver system design. The selected technology for the SKA-low RF signal transportation is RF-over-fiber systems, where the preamplified RF signal picked up by the antennas is carried via analogue modulation over optical fiber. The rationales behind the selection are reported, along with descriptions on the development of the receiver prototypes. The prototypes were deployed and installed on the demonstrator arrays at the selected SKA-low site in Western Australian. Particular attention has been put on the thermal characterization of the receiver system under the actual operating temperature on site, especially when both transmitting part and the optical medium are subjected to external ambient temperature variations. Performance issues encountered in the demonstrator arrays are also discussed along with some proposals for future activities.

Development and Application of a Thermal Comfort Model in Buildings

Buildings are one of the systems that more energy consumed in the European Union. The study of the thermal envelope is interesting in order to reduce the energy losses. For that, a mathematical model able to predict the system response to external temperature variations is developed. With the mathematical model, different thermal envelope elements of a building based on the lag and the cushioning of the resultant wave can be characterized. In addition, it is important to analyse where the insulation is placed, because when the insulation is outside and the thermal mass is inside, the system produces a response with smooth temperature variations than when the insulation is inside. Therefore, placing the outside insulation generates more steady indoor temperatures, increasing the thermal comfort inside the building. To complete the mathematical model that allows predicting the temperature inside a building taking into account the solar inputs and the thermal inertia of the building. This study will help to establish the optimum design parameters in order to build sustainable and comfortable buildings. Furthermore, it will take one step forward in the construction of nearly Zero-Energy Buildings.