Temperature Amplitude Research Articles

Optimization of propolis extraction with natural deep eutectic solvents using central composite design

This study examines the potential of using natural deep eutectic solvents (NADESs) to extract phenolic compounds from propolis and optimizes the extraction process using central composite design (CCD). Different mixtures of NADESs were prepared and analyzed for stability, physicochemical properties, and ability to dissolve phenolic compounds, and four NADES, namely NADES 62 (Betaine, Malic acid and proline 1:1:1, water 15% w/w, NADES 57 (Choline Chloride, Xylitol, Malic Acid 1:1:1, water 15% w/w), NADES 58 (Betaine, Malic acid and proline 1:1, water 15% w/w), NADES 76 (Proline, Citric Acid 2:1 water 15%) were evaluated for the extraction process. The full quadratic model showed that the linear effect of time, temperature, and ultrasound amplitude was found to be significant on the models for NADESs and 80% Ethanol. NADES 62 showed highest extraction yield and the optimal extraction conditions were 80 °C, 135 min, and 100% amplitude. The highest total phenolic and total flavonoid content for NADESs achieved was 5284.2 mg GAE/L and 1531.2 mg QE/L, respectively. With the optimization carried out, the phenolic profile and antimicrobial activity analyses were conducted, has reinforced the information that NADESs can be a good alternative to conventional solvents for propolis extraction.

Key to ENSO phase-locking simulation: effects of sea surface temperature diurnal amplitude

The tendency of El Niño/Southern Oscillation (ENSO) events to peak during boreal winter is known as ENSO phase-locking, whose accurate simulation is essential for ENSO prediction. However, the simulated peaks of ENSO events usually occur outside boreal winter in state-of-the-art climate models. Based on the Coupled Model Intercomparison Project Phase 6 (CMIP6) models, the model with a more reasonable diurnal amplitude (DA) in the sea surface temperature (SST) had a better simulation ability for ENSO phase-locking compared with other models. Further experiments based on the earth system model revealed that the DA is vital for ENSO phase-locking simulation primarily due to the spatial inhomogeneities in seasonal DA anomaly variations in ENSO years with positive/negative DA anomalies in the central equatorial Pacific and negative/positive in the western or eastern Pacific during El Niño/La Niña. Our findings indicate that DA simulation in climate models is crucial for resolving the long-standing failure associated with the ENSO phase-locking simulation accuracy.

Bryophytes dominate plant regulation of soil microclimate in alpine grasslands

Soil temperature and moisture are important regulators of a broad range of biotic and abiotic processes in terrestrial ecosystems. Vegetation can, in turn, play a role in regulating soil microclimate, which creates potential for powerful and interactive feedbacks from soil and vegetation on the atmosphere. Although the regulatory effect of vegetation on soil microclimatic conditions has been quite extensively and empirically assessed, most studies have determined the net effect of intact woody vegetation versus bare ground. However, for other plant functional groups we lack a clear understanding of their role and any climate‐context dependency in controlling microclimatic conditions.We investigated the role of three major plant functional groups – graminoids, forbs and bryophytes – in regulating soil microclimate in semi‐natural alpine grasslands. Using a fully factorial above‐ground biomass removal experiment, we assessed the role of these plant functional groups in regulating soil temperature amplitude, soil moisture, and number of freezing days. The experiment was replicated across orthogonal temperature and precipitation gradients in Norway to assess whether the effects of functional group abundance varied with climate.The effect of plant biomass on soil microclimate varied among functional groups across the climatic gradients. Bryophytes reduced growing season soil temperature, whereas graminoids and forbs did not (0.5ºC compared to 0ºC), and with a stronger effect in colder climates at higher elevations and on days with high solar radiation. Bryophyte biomass further reduced the number of soil freezing days at boreal and sub‐alpine sites. Finally, graminoid biomass partly explained variation in soil moisture: soils dried more under graminoids at drier sites.Our findings highlight that functional group identity plays a key role in regulating soil microclimate in alpine grasslands across seasons. The strong effect of bryophytes on soil temperature points to their importance in the plant community for a variety of ecosystem functions, some of which may be indirectly vulnerable to future warming via biomass reductions of bryophytes.

Co-exposure to highly allergenic airborne pollen and fungal spores in Europe

The study is aimed at determining the potential spatiotemporal risk of the co-occurrence of airborne pollen and fungal spores high concentrations in different bio-climatic zones in Europe. Birch, grass, mugwort, ragweed, olive pollen and Alternaria and Cladosporium fungal spores were investigated at 16 sites in Europe, in 2005–2019. In Central and northern Europe, pollen and fungal spore seasons mainly overlap in June and July, while in South Europe, the highest pollen concentrations occur frequently outside of the spore seasons. In the coldest climate, no allergy thresholds were exceeded simultaneously by two spore or pollen taxa, while in the warmest climate most of the days with at least two pollen taxa exceeding threshold values were observed. The annual air temperature amplitude seems to be the main bioclimatic factor influencing the accumulation of days in which Alternaria and Cladosporium spores simultaneously exceed allergy thresholds. The phenomenon of co-occurrence of airborne allergen concentrations gets increasingly common in Europe and is proposed to be present on other continents, especially in temperate climate.

Experimental investigation of the temperature field of a frost-penetration tunnel based on a whole life cycle laboratory test

Temperature field evolution plays an essential role in anti-freezing design of frost-penetration tunnels, for which temperature data measured throughout the whole life cycle (100 years) are lacking. The spatial and temporal temperature evolution of a frost-penetration tunnel during the whole life cycle was investigated by using a laboratory test. The test model was designed following some basic fundamental assumptions and similarity principles. The proposed test model was validated using typical cases of the long-term evolution of the temperature fields in cold region tunnels. The evolution features, formation mechanisms and influencing factors were deeply discussed. Experimental results of the model test indicate that a frost-penetration phenomenon occurs in tunnels with positive ground temperature and negative mean annual air temperature. Under negative mean annual air temperature, the freezing circle develops radially towards the surrounding rock and simultaneously develops longitudinally along the tunnel after the tunnel breakthrough. The unfrozen surrounding rock freeze yearly and can develop into permafrost. The primary impact factor of frost penetrations is the positive initial ground temperature and negative mean annual air temperature. The mean annual air temperature has an insignificant effect on the annual temperature amplitude of the surrounding rock, whereas the annual air temperature amplitude has a negligible effect on the mean annual temperature.

Analysis of Fluid-Solid Coupling Radial Heat Transfer Characteristics in a Normal Hexagonal Bundle Regenerator under Oscillating Flow

The main purpose of this paper is to analyze the heat transfer mechanism of a new type of regenerator with a low temperature difference and low current resistance under oscillatory flow at room temperature. Taking the single tube of the regenerator as the research object, the exact analytical solution of the radial heat transfer characteristics of the regenerator is obtained by studying its analytical model. The factors affecting the heat transfer characteristics are analyzed, and then the regenerator is optimized to improve the performance and efficiency of the regenerator system. In this study, we systematically analyzed the radial heat transfer characteristics of a regenerator under isochoric process conditions. A closed-system physical model of the incompressible isochoric process under oscillating flow was established. Then, the radial analytical solutions of pressure fluctuation, fluid velocity, fluid-solid temperature, and heat were derived in the complex number field. Furthermore, the fluid velocity, fluid-solid coupling wall temperature, heat, and equivalent heat transfer coefficient were assessed. Furthermore, the influences of frequency, inner diameter R1 of the regenerator, and different working medium and materials on the above parameters were discussed. It was found that the analysis and evaluation of fluid velocity, fluid-structure coupling wall temperature, heat, and equivalent heat transfer coefficient are helpful in understanding the dynamic characteristics of radial heat transfer in a regenerator system. Through the study of radial heat transfer under oscillating flow, it was found that the working medium, frequency, inner diameter of the regenerator, and material quality of the regenerator are helpful for the design optimization of the regenerator. Furthermore, our investigations established that the variation law of wall fluid-solid coupling temperature amplitude could be divided into three parts: the unidirectional flow part; the low-frequency part, where the temperature amplitude falls rapidly with increasing frequency; and the high-frequency part, where the temperature amplitude increases with the frequency. In addition, the variation of radial heat transfer of the fluid-solid coupling surface is similar to the changes in the temperature amplitude. We also discovered that the equivalent heat transfer coefficient of the fluid-solid surface is related to thermal conductivity of the material. Specifically, larger thermal conductivity values result in greater equivalent heat transfer coefficients. Based on the research into the radial heat transfer characteristics, the new regenerator has great application potential in the Stirling air conditioning system at room temperature.

The Role of Water Vapor and Temperature in the Thermodynamics of Tropical Northeast Pacific and African Easterly Waves

Abstract The thermodynamic processes associated with convection in tropical African and northeastern Pacific easterly waves (AEWs and PEWs, respectively) are examined on the basis of empirical orthogonal functions (EOFs) and a plume buoyancy framework. Linear regression analysis reveals the relationship between temperature, moisture, buoyancy, and precipitation in EWs. Plume buoyancy is found to be highly correlated with rainfall in both AEWs and PEWs, and a near 1:1 relationship is found between a buoyancy-based diagnostic of rainfall and rainfall rates from ERA5. Close inspection of the contribution of moisture and temperature to plume buoyancy reveals that temperature and moisture contribute roughly equally to the buoyancy in AEWs, while moisture dominates the distribution of buoyancy in PEWs. A scale analysis is performed in order to understand the relative amplitudes of temperature and moisture in easterly waves. It is found that the smaller contribution of temperature to the thermodynamics of PEWs relative to AEWs is related to their slower propagation speed, which allows PEWs to more robustly adjust to weak temperature gradient (WTG) balance. The consistency of the buoyancy analysis and the scale analysis indicates that PEWs are moisture modes: waves in which water vapor plays a dominant role in their thermodynamics. AEWs, on the other hand, are mixed waves in which temperature and moisture play similar roles in their thermodynamics.

Shallow groundwater temperature patterns revealed through a regional monitoring well network

AbstractGroundwater temperature is a critical control on groundwater quality, geothermal system efficiency and ecosystem dynamics in receiving surface waters. Despite the known importance of groundwater temperature, there is a lack of dedicated aquifer thermal monitoring across spatial and temporal scales. Pressure transducers and other sensors installed in groundwater monitoring well networks often record temperature as a secondary function, but these comprehensive groundwater temperature data sets are seldom analysed. In this study, we analysed seasonal, interannual and spatial patterns of shallow groundwater temperatures from a regional groundwater monitoring network in Nova Scotia, Canada and compared these subsurface temperature data to air temperature data from nearby climate stations using linear regressions and Fourier analysis. The results showed that seasonal groundwater temperatures were damped (with seasonal amplitudes 3.6%–42% of air temperature amplitudes) and lagged (phase shifted 43–145 days) compared to air temperature, with notable year‐to‐year variations in both damping and lagging. Results also highlighted the role of snowpack thickness on the lowest mean monthly groundwater temperatures. Given potential impacts of climate change, land cover change, urbanization and geothermal energy development on groundwater temperatures, we encourage water authorities and regulators to begin or enhance aquifer thermal monitoring and provide guidance for capitalizing on existing monitoring well infrastructure to track temperature dynamics and changes.

Diurnal rhythms of wrist temperature are associated with future disease risk in the UK Biobank

Many chronic disease symptomatologies involve desynchronized sleep-wake cycles, indicative of disrupted biorhythms. This can be interrogated using body temperature rhythms, which have circadian as well as sleep-wake behavior/environmental evoked components. Here, we investigated the association of wrist temperature amplitudes with a future onset of disease in the UK Biobank one year after actigraphy. Among 425 disease conditions (range n = 200-6728) compared to controls (range n = 62,107-91,134), a total of 73 (17%) disease phenotypes were significantly associated with decreased amplitudes of wrist temperature (Benjamini-Hochberg FDR q < 0.05) and 26 (6.1%) PheCODEs passed a more stringent significance level (Bonferroni-correction α < 0.05). A two-standard deviation (1.8° Celsius) lower wrist temperature amplitude corresponded to hazard ratios of 1.91 (1.58-2.31 95% CI) for NAFLD, 1.69 (1.53-1.88) for type 2 diabetes, 1.25 (1.14-1.37) for renal failure, 1.23 (1.17-1.3) for hypertension, and 1.22 (1.11-1.33) for pneumonia (phenome-wide atlas available at http://bioinf.itmat.upenn.edu/biorhythm_atlas/). This work suggests peripheral thermoregulation as a digital biomarker.

Multi-functional conductive cementitious composites including phase change materials (PCM) with snow/ice melting capability

ABSTRACT To remove snow/ice collected on surface of pavements is a must to prevent not only significant structural damages of infrastructures but also traffic accidents, however, today’s methods require higher labour and maintenance costs. Producing phase change materials (PCM)- and carbon fibre (CF)-incorporated multifunctional composites with melting snow/ice capability can be a cost effective alternative compared to mechanical methods and heating systems. In this study, the cementitious composites were produced adding 0, 2, 4, 6 and 8% PCM, by weight of the cement and 0.0, 0.1, 0.3% CF, by volume of the mixture. The composites were compared in means of ice melting performance and the damage resulted from freezing and thawing, applying two different simulations in a freeze–thaw cabinet: −10/+10°C and −20/+20°C. In addition, their compressive strength and consistency results were considered with their SEM analysis. As a result of the studies, the optimum CF ratio, which contributes the most to the melting ice performance of PCM-containing composites, was found to be 0.1% by volume. However, in freeze–thaw simulations, CFs increased the temperature amplitudes and PCMs were able to partially prevent this increase. While PCMs increased the workability of the composites and decreased their strength, CFs adversely affected both their workability and strength.

Adaptive tuning of uncertain parameters in a numerical weather prediction model based upon data assimilation

AbstractIn numerical weather prediction models, near‐surface quantities like 10‐m wind speed (FF10M) or 2‐m temperature (T2M) tend to exhibit significantly larger forecast errors than the related variables in the free troposphere. Besides representativeness issues of surface stations, this is primarily related to parametrization errors and insufficient knowledge of relevant physical properties of the soil and the surface layer. For instance, the vegetation roughness length is usually derived from land‐cover classifications that may contain errors and reflect only part of the natural variability. This article describes a methodology implemented into Deutscher Wetterdienst's operational numerical weather prediction model ICON in order to improve the estimate of such parameters by using information from the data assimilation system. Building upon the condition that FF10M, T2M, and 2‐m relative humidity are assimilated, time‐filtered assimilation increments are calculated for the respective fields at the lowest model level. These are taken as proxies for the related model biases. For T2M, an additional weighted increment field is computed that indicates the model bias in the diurnal temperature amplitude. Based on these increment fields, several physical parameter fields and a few model tuning parameters are varied around their base values. This adaptive parameter adjustment is used operationally in the global and regional forecasting systems of Deutscher Wetterdienst. The ensuing reduction of the FF10M, T2M, and 2‐m relative humidity errors typically lies on the order of 5% on a hemispheric average but has substantial regional and seasonal variability that depends on the original magnitude of the model error. A weaker but still statistically significant positive impact is seen in the radiosonde verification of wind speed, humidity, and temperature in the lower troposphere, giving confidence that the adaptive tuning indeed reduces model errors rather than pushing the model towards unrepresentative station observations.

Biogeography of Fungal Communities Associated with Pinus sylvestris L. and Picea abies (L.) H. Karst. along the Latitudinal Gradient in Europe.

We assessed the diversity and composition of fungal communities in different functional tissues and the rhizosphere soil of Pinus sylvestris and Picea abies stands along the latitudinal gradient of these tree species distributions in Europe to model possible changes in fungal communities imposed by climate change. For each tree species, living needles, shoots, roots, and the rhizosphere soil were sampled and subjected to high-throughput sequencing. Results showed that the latitude and the host tree species had a limited effect on the diversity and composition of fungal communities, which were largely explained by the environmental variables of each site and the substrate they colonize. The mean annual temperature and mean annual precipitation had a strong effect on root fungal communities, isothermality on needle fungal communities, mean temperature of the warmest quarter and precipitation of the driest month on shoot fungal communities, and precipitation seasonality on soil fungal communities. Fungal communities of both tree species are predicted to shift to habitats with a lower annual temperature amplitude and with increasing precipitation during the driest month, but the suitability of these habitats as compared to the present conditions is predicted to decrease in the future.

Le sommeil d’un performeur de l’extrême. Dormir huit jours et sept nuits, assis, sans bouger, enfermé dans une sculpture

Sleep in extreme situations has been little studied. The artist Abraham Poincheval (AP) is known for his performances in confined spaces. For his show at the Perrotin Gallery in Paris, he was enclosed for 8days and 7nights in a metal sculpture of his body in a seated position, with his head facing a work by Hans Hartung at the end of a cone system placed in front of his eyes which occluded all other visual stimuli. The interior of the metal structure was not padded and there was no head support. His sleep and internal temperature were continuously recorded using polysomnography (Grael, Compumedics) and an orally swallowed temperature sensitive capsule (Bodycap) with temperature sampling every 2min. AP slept an average of 355.1min/24h, composed of light slow-wave sleep (N1: 47.1min, N2: 192.2min), deep slow-wave sleep (N3: 100.4min), and REM sleep 4,3 % (15.4min). Sleep, although mostly nocturnal, was split into periods of no more than 20min. Deep sleep was therefore remarkably resistant to the uncomfortable experimental conditions, while REM sleep was markedly impaired, lasting only a few short minutes and followed by rapid awakening. This is probably due to the head position within the sculpture which was unsupported, so REM sleep with its inherent muscle atonia led to involuntary head flexion and was impossible to sustain for long. The thermal minimum was between 5:17 a.m. and 6:35 a.m. The amplitude of the core temperature decreased by more than 30 % between the beginning and the end of the protocol. Despite the immobility induced by the confined experimental conditions, there was no desynchronization of circadian rhythms. The sleep time was surprisingly long given the conditions, and slow-wave sleep was relatively preserved with an amount typically found in normal subjects while REM sleep was markedly impaired. Slow-wave sleep is clearly preserved underlying its central role in physical and mental homeostasis. REM sleep is clearly more fragile. The reduction in REM sleep linked to position has been found in a study of sleep in the sitting position in airplanes where loss of muscle tonus in the neck fragments REM sleep. Techniques for selective REM sleep deprivation also use muscle atonia: one of the initial techniques of selective REM sleep deprivation relied on muscle atonia in REM causing a cat to fall from a small perch into water. In man, the lack of head support is clearly a source of REM fragmentation. However in the case of this study, we cannot exclude an effect of other factors, notably the meditative techniques used by the performer to maintain attention on the painting, described as a dream state punctuated by visual hallucinations. Surprisingly, despite physical isolation within the sculpture, AP's biological rhythms remained stable. However, the conditions were not those of complete isolation: noise, the presence of the public in the gallery who occasionally talked to AP through the sculpture, and variations in light during the day were all temporal cues. In addition, a heatwave during the performance raised the temperature in the room with reduced total sleep time on the hottest night. Although the phase of the circadian rhythm measured by the internal temperature did not change, the amplitude fell which is compatible with reduced physical activity. In conclusion, under physically constraining and uncomfortable sleep conditions, deep sleep is maintained while REM sleep is starkly reduced. From a homeostatic point of view, this means that over a short period of time, in a survival situation, energy recovery through deep slow-wave sleep takes priority over REM sleep.

Low cycle fatigue and fatigue-creep interaction effects on softening behavior and life prediction of cast aluminum alloy at elevated temperature

In this study, a series of strain-controlled low-cycle-fatigue (LCF) and low-cycle-fatigue-creep (LCFC) experiments were conducted on a cast Al-Si-Cu alloy. LCF and LCFC experiments were performed at 250 ℃, 300 ℃ and 350 ℃ with three different strain amplitudes. The results showed significant softening behavior, with temperature affecting both the softening behavior and fatigue life. Interestingly, coupling creep at 250 ℃ was found to increase fatigue life. Microstructure evolution was investigated by using scanning electron microscopy, and it was found that the introduction of strain-dwell at the tensile peak caused the interaction of fatigue and creep, resulting in a large amount of plastic deformation that affected fatigue life. Two fracture models were proposed for LCF and LCFC tests at different temperatures, based on the microstructure evolution. Using the experimental data, a modified life prediction model was proposed, which demonstrated a better prediction ability than other traditional models in fatigue-creep life prediction under different temperature and strain amplitudes.

The low cycle fatigue property, damage mechanism, and life prediction of additively manufactured Inconel 625: Influence of temperature

AbstractSymmetrical high‐temperature low‐cycle fatigue tests were performed in this study to examine the influence of temperature on the fatigue failure mechanism of the additively manufactured Inconel 625. According to the fracture analysis, cracks initiate from the crystallographic plane at room temperature. At 600°C, oxidation of carbides leads to crack initiation. The strengthening effect of γ″ precipitation prevents crack propagating within the matrix. At 750°C, the crack becomes transgranular propagating, as a consequence of γ″‐δ transformation. Geometrically necessary dislocations distribution on the fracture supports this result. Furthermore, a modified life prediction formula considering effect of temperature and strain amplitude was established. It was observed that the modified model predicted the fatigue life of the studied materials well in both test conditions.

An experimental study on aging effects of the air–fuel ratio swing on modern gasoline three-way catalysts

Today’s governmental legislations require region specific emission standards for passenger vehicles. Continuously increasing legal requirements demand the development of more complex exhaust gas after treatment systems to further reduce harmful gases like carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx). Due to specific load profiles and other boundary conditions, the efficiency of the aftertreatment system declines over lifecycle, so that the emissions might increase. Consequently, the durability of the system becomes a critical design parameter with upcoming legislation demanding emissions stability over the vehicle life cycle. Within this publication, catalyst aging effects due to air–fuel ratio (AFR) swing are analyzed experimentally. To create catalyst aging conditions, a modern eight-cylinder turbocharged engine was modified and specific aging cycles with a variation of AFR swing amplitude and frequency were conducted. Light-off curves were used to depict the negative impact of the AFR swing on the aging catalyst systems. A higher swing frequency resulted in an increased temperature amplitude within the entrance area of the catalyst, while an elevated amplitude lead to more exothermic heat release and stronger aging over the complete catalyst, as visualized via conversion maps. A theoretical calculation of thermal loads by Arrhenius equation supports the results and indicates the direction of supplementary experimental approaches.

Research on thermal- humidity -force coupling characteristics of mass concrete structures under temperature control

Hydraulic mass concrete has been in a temperature and humidity cycle environment for a long time, reducing the performance and service life of its structure. Under the premise of temperature control, we use the Soret effect as the basis of heat- humidity coupling, and then use thermal conductivity, diffusion coefficient and elastic modulus to evaluate the coupling effect between temperature, relative humidity, and stress of mass concrete, and establish a thermal – humidity -force coupling model. Using the embedded temperature and humidity sensor to conduct experiments on mass concrete, this study explores the temperature control pipeline's influence on the temperature and relative humidity distribution inside the concrete and the feasibility of the coupling model. Through experimental results and model analysis, this study found that, under temperature control, the prediction results of the coupled model are more consistent with the experimental results, and its accuracy is higher than that of the uncoupled model. In the process of temperature control, temperature has a significant effect on surface water diffusion, whereas humidity has little effect on temperature conduction, and temperature conduction is mainly affected by temperature gradient. Temperature control can effectively reduce the temperature amplitude inside the concrete, reducing the stress inside the concrete. Moreover, the coupled thermal-moisture-force model can accurately predict the variation trend of temperature, relative humidity, and stress with time at each point inside the concrete under temperature control. The theoretical results of this study can provide a reference for the design, construction, and maintenance of hydraulic engineering structures in the future and better grasp the internal temperature, relative humidity, and stress of hydraulic concrete in different environments and the change law.

Optimization of Ultrasound-Assisted Cold-Brew Method for Developing Roselle (Hibiscus sabdariffa L.)-Based Tisane with High Antioxidant Activity

Edible flowers, including roselle, contain a varied composition of phenolic compounds that may inhibit the oxidative stress mechanism. Roselle-based tisane with appealing sensory properties is commonly consumed worldwide. However, the conventional hot-brew method may ruin the stability of thermolabile phenolic compounds during the tisane preparation. Hence, this study aimed to develop a new alternative brewing method linked with the new cold-brew method, which involves a lower temperature and applying ultrasound to maximize the extraction of phenolic compounds and to avoid degradation during the tisane preparation. The brewing factors, including particle size (10, 20, 30 mesh), temperature (4, 15, 26 °C), time (10, 20, 30 min), and ultrasound amplitude (20, 60, 100% of the maximum amplitude) have been optimized simultaneously using Box–Behnken design in conjunction with response surface methodology. Seven major phenolic compounds were identified by HPLC-DAD and classified into hydroxycinnamic acid derivatives (HCA) and flavonoids. The optimum extraction condition to reach the highest level of the studied phenolic compounds was set to brew roselle with particle size of 30 ± 3.25 mesh at 26 ± 1.32 °C for 18 ± 2.00 min applying 78 ± 5.64% ultrasound amplitude. This method successfully extracted almost all HCA and flavonoid during the first cycle with less than 10% CV and provided higher antioxidant activity in terms of DPPH (IC50 9.77 ± 0.01 µg mL−1), ABTS (IC50 8.05 ± 0.02 µg mL−1), and FRAP (IC50 10.34 ± 0.03 µg mL−1) than the roselle tisane prepared using the conventional method. Additionally, the resulting cold-brew product was stable for up to five days of storage.

Thermal Fatigue Crack Propagation Process and Mechanism of Multicomponent Al-7Si-0.3Mg Alloy

The thermal fatigue behavior of multicomponent Al-7Si-0.3Mg alloys in four different treatment states at typical temperature amplitudes 20 °C→350 °C was studied. The morphology of the second phase particles and crack propagation, and distribution characteristics of dislocations in the thermal fatigue specimens of multicomponent Al-7Si-0.3Mg alloys, were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX spectrum), and transmission electron microscopy (TEM). The influencing factors, the process, and the mechanism of thermal fatigue crack propagation were mainly studied. The results show that under the same temperature amplitude, the thermal fatigue properties and dislocation densities of the new aluminum alloy and the new aluminum alloy under T6 heat treatment are significantly higher than that of the multicomponent Al-7Si-0.3Mg alloy in cast and refined and modified treatment. The crack growth of thermal fatigue specimen depends on three factors: the temperature amplitude, oxidation, and residual stress. The process of thermal fatigue crack propagation mainly experiences crack initiation and the formation of microcracks, but only a few microcracks continue to expand rapidly or preferentially expand into main cracks. The mechanism of thermal fatigue crack propagation is mainly under the action of thermal stress, the crack tip undergoes a cycle of repeated alternation of sharpening → passivation → sharpening, and the crack continues to move forward from its tip intermittently in the way of propagation → stopping → propagation until fracture failure.

Tests and Micro–Macro Cross-Scale Model of High-Performance Acrylate Viscoelastic Dampers Used in Structural Resistance

This study aims to develop a high-performance acrylate viscoelastic damper (HAVED), which is suitable for the low-frequency vibration control of building structures. To reveal the influence of ambient temperature, excitation frequency, and displacement amplitude on the dynamic mechanical performance and energy dissipation capacity of a HAVED, a series of dynamic mechanical performance tests were performed on a HAVED within the extensive temperature (10°C–50°C), frequency (0.1–3 Hz), and displacement (0.5–4 mm) range. The analysis results show that a HAVED has excellent energy dissipation capacity and good adaptability to the external environment. The loss factor of a HAVED can reach up to 1.85, and it remains above 0.28 even in a high-temperature environment of 50°C. The dynamic mechanical properties and energy dissipation capacity of a HAVED show strong dependences and obvious coupling effects on temperature, frequency, and displacement amplitude. Based on the experimental research of a HAVED, the micromechanical properties of viscoelastic materials are analyzed, and the high-order fractional derivative model is used to comprehensively describe the mechanical characterization of microscopic molecular chains. The Kraus theory is introduced to consider the influence of filler particles, and the high-order fractional derivative micro–macro cross-scale mathematical model is proposed by combining with the temperature-frequency equivalence principle. Through the experimental results, the prediction capabilities of the model that have been established have been verified. The analysis results show that the proposed model can comprehensively describe the influence of ambient temperature, excitation frequency, displacement amplitude, microscopic molecular chain structure, and filler particles on the mechanical properties of a HAVED.