Small Temperature Fluctuations Research Articles

Test operation of microwave-assisted chemical looping gasification for water hyacinth with a lean iron ore as oxygen carrier

Chemical looping gasification has been considered as a promising biomass energy conversion technology for syngas production. In this work, a novel microwave-assisted chemical looping gasification (MACLG) reactor system is applied to water hyacinth with a lean iron ore as the oxygen carrier (OC). This approach is expected to achieve effective gasification performance with fast heating and small temperature fluctuation. MACLG can promote the proportion of syngas to 74.39%, lower heating value to 11.83 MJ/Nm3 and cold gasification efficiency to 80.94%. In addition, the increase of OC has a great effect on the conversion of water hyacinth. Favorable gasification performance, including total gas yield, H2/CO ratio, carbon conversion efficiency, and OC reactivity, can be achieved when the molar ratio of Fe2O3/C is in the range of 0.25–0.50. Furthermore, a moderate temperature is also vital for reaction effect. With a temperature of 900 °C, the highest H2/CO ratio of 1.37 of syngas is obtained.

Parameterization optimal control of an unsteady partial differential equations with convection term by an improved three-term spectrum conjugate gradient algorithm

The unsteady partial differential equations (UPDE) with convection term gives a clear descriptions for the solidification process of a slab in dynamic production of continuous casting. To give a suitable setting value of secondary cooling water flow rate for the dynamic control system, this study investigates an optimal control problem (OCP) of UPDE with convection term. Firstly, control vector discretization of OCP and the solution of UPDE are given. Secondly, due to the rapidity for gradient, this paper analyzes the expression of the gradient calculation method based on Hamiltonian function costate system by approximate treatment, matrix calculation and composite trapezoidal integral method. Thirdly, an improved three-term spectrum conjugate gradient algorithm (ITSCGA) is proposed to solve the OCP of UPDE, and the global convergence of the ITSCGA is demonstrated. Lastly, the performance of ITSCGA is demonstrated by experimental simulations. The results demonstrate that the ITSCGA provides a smaller temperature fluctuations, and improves the quality of a slab.

A ratiometric fluorescent fiber sensor based on integrated silica and tellurite glass for real-time human thermal monitoring

In this paper, we propose and demonstrate a portable fiber sensor with integrated tellurite and silica for dynamic human thermal monitoring, where Er3+/Yb3+ co-doped tellurite glass is employed to generate upconversion fluorescence emission related to thermally coupled energy levels via near-infrared excitation for ratiometric thermometry. The molten tellurite glass is extracted into a silica tube using the negative pressure approach, allowing for intimate adhesion between different glass materials with considerable softening temperature differences. With a fast instantaneous response of 0.4–0.6 s and an absolute error of −0.45–0.36 K, the sensor can accurately and timely capture small temperature fluctuations. The sensor is placed in the mouth or attached to the hand skin to measure the body temperature continually. It is also positioned in the mouth exhalation and nose breathing environments to monitor thermal activities in real-time, offering a new, highly reliable method for human health monitoring.

Ionic Gel Based Multifunctional Sensor for Body Temperature Monitoring and Joint Motion Detection

Flexible temperature and strain sensors are key components of wearable devices for healthcare monitoring. Currently, the insufficient precision, undesirable mechanical properties, and the cross interference between different external stimuli are still bottleneck problems for flexible sensors especially in body temperature and human motion monitoring. Herein, an ionic gel based on ionic liquids (ILs) and commercial thermoplastic polyurethane (TPU) fiber is fabricated via a feasible and scalable immersion method for temperature and strain multifunctional sensing. Wearable sensor based on ionic gel exhibits high temperature sensitivity (2.73% ◦C−1) and sufficient resolution (0.1 ◦C) in the skin temperature range. Meanwhile, the sensor exhibits linear and stable strain sensing performance and has the ability to respond to tiny strains. More importantly, the multifunctional fiber‐like sensor is easy to integrate with traditional textile, which is beneficial to solve the wearability problems such as discomfort and impermeability in practical applications. Notably, the stimulus caused by strain can be almost avoided by sewing smart fibers into S‐shape during the temperature monitoring, which helps decouple the temperature and strain signals. As prepared intelligent textiles can accurately capture small fluctuations in temperature and detect the action amplitude of the human body, which is important for disease prediction and rehabilitation training of patients.

Geometry Controlled Oscillations in Liquid Crystal Polymer Films Triggered by Thermal Feedback.

Light-induced oscillatory behavior of liquid crystal polymer network (LCN) films has been demonstrated by several researchers in the past decade. Similarly, oscillations in LCN films under constant thermal stimulus have been reported recently, although the mechanism and the factors that govern the oscillatory behavior are not well understood. In this work, we study the dynamics of self-sustained oscillations exhibited by LCN films under a constant thermal stimulus through experiments and simulations. Geometrically asymmetric films such as a right triangle and an equilateral triangle are obtained from a twisted nematic square film. A multiphysics computational framework using the finite element method is developed to simulate the oscillatory behavior of the LCN films kept on a hot plate. The framework accounts for a coupling between heat transfer and mechanical deformations during the oscillations. Small temperature fluctuations (≈ 1 °C) coupled with gravity induced torque are shown to drive the oscillatory behavior at a specific plate temperature. We show for the first time that self-sustained oscillations can also be achieved in symmetric shapes, such as square films, by creating a thickness tapering between two opposite edges. The frequency of the oscillations is found to be in the range of 0.5 to 2.5 Hz for different geometries studied. The oscillation temperature depends on the mean thickness, size, and thickness profile of the films. As a possible application, we demonstrate a thermally actuated optical chopper using the oscillatory response of the films.

Qualitative Comparison of Lock-in Thermography (LIT) and Pulse Phase Thermography (PPT) in Mid-Wave and Long-Wave Infrared for the Inspection of Paintings

When studying paintings with active infrared thermography (IRT), minimizing the temperature fluctuations and thermal shock during a measurement becomes important. Under these conditions, it might be beneficial to use lock-in thermography instead of the conventionally used pulse thermography (PT). This study compared the observations made with lock-in thermography (LIT) and pulse phase thermography (PPT) with halogen light excitation. Three distinctly different paintings were examined. The LIT measurements caused smaller temperature fluctuations and, overall, the phase images appeared to have a higher contrast and less noise. However, in the PPT phase images, the upper paint layer was less visible, an aspect which is of particular interest when trying to observe subsurface defects or the structure of the support. The influence of the spectral range of the cameras on the results was also investigated. All measurements were taken with a mid-wave infrared (MWIR) and long wave infrared (LWIR) camera. The results show that there is a significant number of direct reflection artifacts, caused by the use of the halogen light sources when using the MWIR camera. Adding a long-pass filter to the MWIR camera eliminated most of these artifacts. All results are presented in a side-by-side comparison.

Photoexcited Ultraviolet‐to‐Infrared (II) Pyroelectricity in a 2D Ferroelectric Perovskite Driving Broadband Self‐Powered Photoactivities

AbstractPhotoexcited pyroelectricity in ferroelectrics allows the direct conversion of light radiation into electric signal without external power source, thus paving an avenue to promote optoelectronic device performances. However, it is urgently demanded to exploit new ferroelectrics with this attribute covering ultraviolet (UV)‐to‐infrared (IR) region for self‐powered photodetection. Herein, broadband light‐induced pyroelectric effects in a new 2D perovskite‐type ferroelectric, (BBA)2(EA)2Pb3Br10 (1; BBA = p‐bromobenzylammonium, EA = ethylammonium), showing a high Curie temperature of 425 K and notable pyroelectric coefficient (≈5.4 × 10−3 µC cm−2 K−1) is presented. Especially, photo‐induced change of its electric polarization leads to ultraviolet‐to‐infrared pyroelectricity in a wide spectral region (377–1950 nm). Broadband photoactivities actualized by this property break the limitation of its optical bandgap. Thus, single‐crystal detectors of 1 are sensitive to UV‐to‐IR light with a small temperature fluctuation of 0.3 K, exhibiting a high transient responsivity up to ≈0.28 mA W−1 and specific detectivity of 1.31 × 1010 Jones under zero bias (at 405 nm); such figure‐of‐merits are beyond than those self‐powered photodetectors using oxide ferroelectrics. It is anticipated that the findings of light‐induced pyroelectricity afford a feasible strategy to assemble newly‐conceptual smart photoelectric devices, such as self‐powered broadband detectors.

A ±0.5-mV-Minimum-Input DC-DC Converter With Stepwise Adiabatic Gate-Drive and Efficient Timing Control for Thermoelectric Energy Harvesting

This paper presents a step-up DC-DC converter that uses a stepwise gate-drive technique to reduce the power FET gate-drive energy by 82%, allowing positive efficiency down to an input voltage of ±0.5 mV—the lowest input voltage ever achieved for a DC-DC converter as far as we know. Below ±0.5 mV the converter automatically hibernates, reducing quiescent power consumption to just 255 pW. The converter has an efficiency of 63% at ±1 mV and 84% at ±6 mV. The input impedance is programmable from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1~\Omega $ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$600~\Omega $ </tex-math></inline-formula> to achieve maximum power extraction. A novel delay line circuit controls the stepwise gate-drive timing, programmable input impedance, and hibernation behavior. Bipolar input voltage is supported by using a flyback converter topology with two secondary windings. A generated power good signal enables the load when the output voltage has charged above 2.7 V and disables when the output voltage has discharged below 2.5 V. The DC-DC converter was used in a thermoelectric energy harvesting system that effectively harvests energy from small indoor temperature fluctuations of less than 1°C. Also, an analytical model with unprecedented accuracy of the stepwise gate-drive energy is presented.

Unexpected luminescence of non-conjugated biomass-based polymers: new approach in photothermal imaging.

Population growth, depletion of world resources and persistent toxic chemical production underline the need to seek new smart materials from inexpensive, biodegradable, and renewable feedstocks. Hence, "metal-free" ring-opening copolymerization to convert biomass carvone-based monomers into non-conventional luminescent biopolymers is considered a sustainable approach to achieve these goals. The non-conventional emission was studied in terms of steady-state and time-resolved spectroscopy in order to unravel the structure-properties for different carvone-based copolymers. The results highlighted the importance of the final copolymer folding structure as well as its environment in luminescent behavior (cluster-triggered emission). In all cases, their luminescent behavior is sensitive to small temperature fluctuations (where the minimum detected temperature is Tm ∼ 2 °C and relative sensitivity is Sr ∼ 6% °C) even at the microscopic scale, which endows these materials a great potential as thermosensitive smart polymers for photothermal imaging.

SrB4O7:Sm2+ fluorescence improves the accuracy of temperature measurements in externally heated diamond anvil cells.

The sample temperature in an externally heated diamond anvil cell (EHDAC) is generally measured by a thermocouple fixed to the pavilions of diamond anvils, ignoring the temperature difference between the thermocouple and the sample. However, the measured temperature depends strongly on the placement of the thermocouple, thus seriously reducing the accuracy of the temperature measurement and hindering the use of EHDAC in experiments requiring precise temperature measurements, such as high-pressure melting and phase-diagram investigations. In this study, the full width at half maximum (FWHM) of the 0-0 fluorescence line of strontium borate doped with bivalent samarium ions (SrBO4:Sm2+, SBO) is found to be highly sensitive to temperature and responds extremely rapidly to small temperature fluctuations, which makes it an excellent temperature indicator. We propose herein a precise method to measure temperature that involves measuring the FWHM of the 0-0 fluorescence line of SBO. This method is used to correct the temperature discrepancy between the thermocouple and the sample in an EHDAC. These corrections significantly improve the accuracy of temperature measurements in EHDACs. The accuracy of this method is verified by measuring the melting point of tin at ambient pressure. We also use this method to produce a tentative elementary phase diagram of tin up to 109GPa and 495K. This method facilitates high-pressure, high-temperature experiments demanding accurate temperature measurements in various disciplines. The study also discusses, in general, the experimental approach to measuring temperature.

Control strategy of load following for ocean thermal energy conversion

Ocean thermal energy conversion (OTEC) provides a feasible solution for sustainable and stable power supply in remote islands. In this paper, a thermodynamic model of the OTEC system is developed to study the dynamic response of power output and superheating degree to manipulated variables. Afterward, a control strategy of load following for the island OTEC system is proposed. Finally, two controllers, MPC and PI, are designed and compared under fast and slow load changes as well as disturbance rejection test. The results indicate that the power output of OTEC system is sensitive to the speed of working-fluid pump, reaching the adjustment range of 14.7 kW when the nominal speed decreases by 30%. In addition, model predictive control (MPC) shows better performance in both rapid and slow load-change modes. Especially, in the rapid load-change mode, the MPC controller could always keep the evaporator outlet superheating in the range of 2–4.5 °C, while the PI controller may introduce no superheat that may cause liquid impact. Both MPC and PI controller can stabilize the power output at the set point under one day's measured disturbance, while MPC controller makes the superheating degree of evaporator outlet within smaller temperature fluctuations (<0.2 °C).

The Effect of Banning Fireworks on Air Quality in a Heavily Polluted City in Northern China During Chinese Spring Festival

Air pollution has a negative impact on the ecological environment as well as on the health of people. Setting off fireworks and firecrackers lead to a significant deterioration in air quality in a short period of time. The firework prohibition policy of 2016 in Zhengzhou City provides an opportunity to investigate the effect of banning fireworks on air quality during the Spring Festival. The Air Quality Index and the concentrations of PM2.5, PM10, SO2, NO2, CO and O3 during the Spring Festival between 2014 and 2019 in Zhengzhou City were analyzed. The results show that: There were small fluctuations in precipitation, air pressure, wind speed, temperature and relative humidity during the Spring Festival from 2014 to 2019. The air quality index in the Spring Festival in 2016 was significantly lower than that in 2014 and 2015, and the air quality in 2018 and 2019 showed greater improvements. The sudden increases in pollutants concentrations has been weakened, showing an obvious “peak-shaving” effect during the traditional heavy pollution period, New Year’s Eve to the first day of the first lunar month. In 2014 and 2015 years, the concentrations of PM2.5 and PM10 reached their peaks at 1:00 a.m. on the first day of the new year, and fluctuated in the ranges of 259–271 μg/m³ and 380–384 μg/m³, respectively. The concentrations of PM2.5 and PM10 were 44 and 100 μg/m³, respectively in 2016, 40 and 80 μg/m³ in 2018 during the same period. In addition, the ban implemented has the most obvious impact on PM2.5 and PM10. Compared with the Spring Festival in 2014, the concentrations of PM2.5 and PM10 increased by 19.15 and 18.64% in 2015, decreased by 18.38% and 15.90% in 2016, and decreased by 16.83% and 26.05% in 2018. Therefore, banning fireworks and firecrackers will help to improve the air quality during the Spring Festival in Zhengzhou City to a certain extent.

Low-energy probes of the small cosmic microwave background amplitude in models of the radiative Higgs mechanism

Abstract The small cosmic microwave background (CMB) amplitude As ≃ 10−9 (or small temperature fluctuation δT/T ≃ 10−5) typically requires an unnaturally small effective coupling of an inflaton λϕ ∼ 10−14. In models with non-minimal coupling ξ, extra suppression of the amplitude, e.g. by the inflaton’s large field values, usually allows λϕ to be much larger, but at the price of ξ ≫ 1. Although the difficulties have not been strictly quantified, models with λϕ ≪ 1 or ξ ≫ 1 are harder to build. We show that the absence of new physics signals at TeV scale can suggest a relatively small $\xi \lesssim {\cal O}(1\mbox{--}100)$ with $\lambda _\phi \lesssim {\cal O}(10^{-4}\mbox{--}10^{-8})$, while constraining larger ξ with larger λϕ more strongly. Above all, this is possible by a connection between low- and high-energy physics that can be made in scenarios where the U(1)X Higgs is an inflaton at a high scale while its renormalization running also induces the Coleman–Weinberg mechanism for the electroweak symmetry breaking at a low scale. The best TeV-scale signals are Z′ resonances and Higgs signal strengths. We further find the connection particularly useful since the Z′ mass is upper bounded in order to produce the correct As and the weak scale simultaenously. Utilizing the intriguing upper bounds, we work out the prospects for LHC 13 and 100 TeV pp colliders probing the parameter space of the small CMB amplitude in such a model.

Intrinsic network activity reflects the fluctuating experience of tonic pain.

Although we know sensation is continuous, research on long-lasting and continuously changing stimuli is scarce and the dynamic nature of ongoing cortical processing is largely neglected. In a longitudinal study, 38 participants across four sessions were asked to continuously rate the intensity of an applied tonic heat pain for 20min. Using group-independent component analysis and dual regression, we extracted the subjects' time courses of intrinsic network activity. The relationship between the dynamic fluctuation of network activity with the varying time courses of three pain processing entities was computed: pain intensity, the direction of pain intensity changes, and temperature. We were able to dissociate the spatio-temporal patterns of objective (temperature) and subjective (pain intensity/changes of pain intensity) aspects of pain processing in the human brain. We found two somatosensory networks with distinct functions: one network that encodes the small fluctuations in temperature and consists mainly of bilateral primary somatosensory cortex (SI), and a second right-lateralized network that encodes the intensity of the subjective experience of pain consisting of SI, secondary somatosensory cortex, the posterior cingulate cortex, and the thalamus. We revealed the somatosensory dynamics that build up toward a current subjective percept of pain. The timing suggests a cascade of subsequent processing steps toward the current pain percept.

Performance studies on vapour compression refrigeration system using PCM placed between wall and coil of the evaporator

The vapour compression refrigeration system (VCRS) plays a vital role in the food preservation and it consumes more energy. The use of energy-efficient refrigerants, phase change materials (PCMs) in the condenser and evaporator, and the replacement of existing components, as well as nano-refrigerants, are all efforts made to increase the energy efficiency of the VCRS from different perspectives. Among them, the PCMs play a prominent role and gives sustainable energy efficiency in VCRS. This paper investigates and clarifies the energy efficiency of VCRS can be improved by incorporating a PCM into the evaporator cabin. The experimental results demonstrated substantial effects on system performance such as an improvement in COP of 7.1%, a decrease in per day energy consumption by 6.7%, and comparatively smaller temperature fluctuations within the freezer cabinet. The exergy efficiency is increased and Total Equivalent Warming Impact (TEWI) is decreasing than that of the system without PCM by 7.6 and 7% respectively. This technique is integrated into the VCRS, leading to savings in energy while also being useful for power interruptions common in areas with low grid reliability.

Recent Advances in Polymer-Containing Multifunctional Phase-Change Materials.

Phase-change materials (PCMs) play a key role in thermal energy storage owing to their high-energy storage density and small temperature fluctuation during the phase-transition stage. Polymers, either as a supporting material to prevent liquid leakage during the phase-change process or used with specific target, have been widely recognized in the fabrication of PCM composites. In the meantime, due to the continued demand for variety of PCMs, a single thermal energy storage function seems to be insufficient to meet these needs. Thanks to the good compatibility with PCMs and the structural adjustable properties of polymers, they have been broadly used as the second component in the multifunctional PCMs composite. In this Review, strategies for multifunctional PCMs supported by polymers and their potential energy applications, such as thermal energy harvesting and storage, shape memory, wearable devices, self-cleaning, and other forms of applications, are summarized comprehensively. The future research directions and challenges of multifunctional PCMs with polymers are also discussed.

Energy Conversion from Heat to Electricity by Highly Reversible Phase-Transforming Ferroelectrics

Searching for performant multiferroic materials attracts general research interests in energy science as they have been increasingly exploited as the conversion media among thermal, electric, magnetic and mechanical energies by using their temperature-dependent ferroic properties. Here we report a material development strategy that guides us to discover a reversible phase-transforming ferroelectric material exhibiting enduring energy harvesting from small temperature differences. The material satisfies the crystallographic compatibility condition between polar and nonpolar phases, which shows only 2.5C thermal hysteresis and high figure of merit. It stably generates 15uA electricity in consecutive thermodynamic cycles in absence of any bias fields. We demonstrate our device to consistently generate 6uA/cm2 current density near 100C over 540 complete phase transformation cycles without any electric and functional degradation. The energy conversion device can light up a LED directly without attaching an external power source. This promising material candidate brings the low-grade waste heat harvesting closer to a practical realization, e.g. small temperature fluctuations around the water boiling point can be considered as a clean energy source.

Light-Off in Plasmon-Mediated Photocatalysis.

In plasmon-mediated photocatalysis it is of critical importance to differentiate light-induced catalytic reaction rate enhancement channels, which include near-field effects, direct hot carrier injection, and photothermal catalyst heating. In particular, the discrimination of photothermal and hot electron channels is experimentally challenging, and their role is under keen debate. Here we demonstrate using the example of CO oxidation over nanofabricated neat Pd and Au50Pd50 alloy catalysts, how photothermal rate enhancement differs by up to 3 orders of magnitude for the same photon flux, and how this effect is controlled solely by the position of catalyst operation along the light-off curve measured in the dark. This highlights that small fluctuations in reactor temperature or temperature gradients across a sample may dramatically impact global and local photothermal rate enhancement, respectively, and thus control both the balance between different rate enhancement mechanisms and the way strategies to efficiently distinguish between them should be devised.

Tundra Type Drives Distinct Trajectories of Functional and Taxonomic Composition of Arctic Fungal Communities in Response to Climate Change - Results From Long-Term Experimental Summer Warming and Increased Snow Depth.

The arctic tundra is undergoing climate-driven changes and there are serious concerns related to the future of arctic biodiversity and altered ecological processes under possible climate change scenarios. Arctic land surface temperatures and precipitation are predicted to increase further, likely causing major transformation in terrestrial ecosystems. As a response to increasing temperatures, shifts in vegetation and soil fungal communities have already been observed. Little is known, however, how long-term experimental warming coupled with increased snow depth influence the trajectories of soil fungal communities in different tundra types. We compared edaphic variables and fungal community composition in experimental plots simulating the expected increase in summer warming and winter snow depth, based on DNA metabarcoding data. Fungal communities in the sampled dry and moist acidic tundra communities differed greatly, with tundra type explaining ca. one-third of compositional variation. Furthermore, dry and moist tundra appear to have different trajectories in response to climate change. Specifically, while both warming and increased snow depth had significant effects on fungal community composition and edaphic variables in dry tundra, the effect of increased snow was greater. However, in moist tundra, fungal communities mainly were affected by summer warming, while increased snow depth had a smaller effect and only on some functional groups. In dry tundra, microorganisms generally are limited by moisture in the summer and extremely low temperatures in winter, which is in agreement with the stronger effect of increased snow depth relative to warming. On the contrary, moist tundra soils generally are saturated with water, remain cold year-round and show relatively small seasonal fluctuations in temperature. The greater observed effect of warming on fungi in moist tundra may be explained by the narrower temperature optimum compared to those in dry tundra.

Passive distributed temperature sensing (PDTS)-based moisture content estimation in agricultural soils under different vegetative canopies

A semi-empirical Boltzmann model is proposed to describe the relationship between the rate of temperature increase and soil moisture content, which can replace the existing complicated numerical iterative algorithm. The proposed method greatly simplifies the calculation process and improves the applicability of the passive distributed temperature sensing (PDTS) technology. A field test was performed in the Loess Plateau of China to validate the capability of this method. The field site has four typical land cover conditions: bare soil (G1), plastic mulch (G2), plastic mulch cover with potatoes (G3), and plastic much cover with maize (G4). The monitoring results indicate that for G1 and G2, the relationship between soil moisture content and the rate of temperature increase can be quantitatively described by the Boltzmann model with a root-mean-square error of 0.024 m3/m3. For G3, a linear relationship is found. In contrast, the PDTS technology is not applicable for G4 because a constant ground surface heat power from solar radiation and small air temperature fluctuations are preconditions of PDTS. If the coefficient of determination (R2) for fitting rate of temperature increase is larger than 0.9, the ground surface heat power by solar radiation can be considered as a constant.