Large Temperature Fluctuations Research Articles

Characterization of carbon dioxide on Ganymede and Europa supported by experiments: Effects of temperature, porosity, and mixing with water

The surfaces of icy moons are primarily composed of water ice that can be mixed with other compounds, such as carbon dioxide. The carbon dioxide (CO$_2)$ stretching fundamental band observed on Europa and Ganymede appears to be a combination of several bands that are shifting location from one moon to another. We investigate the cause of the observed shift in the CO$_2$ stretching absorption band experimentally. We also explore the spectral behaviour of CO$_2$ ice by varying the temperature and concentration. We analyzed pure CO$_2$ ice and ice mixtures deposited at 10 K under ultra-high vacuum conditions using Fourier-transform infrared (FTIR) spectroscopy and temperature programmed desorption (TPD) experiments. Laboratory ice spectra were compared to JWST observation of Europa's and Ganymede's leading hemispheres. The simulated IR spectra were calculated using density functional theory (DFT) methods, exploring the effect of porosity in CO$_2$ ice. Pure CO$_2$ and CO$_2$-water ice show distinct spectral changes and desorption behaviours at different temperatures, revealing intricate CO$_2$ and H$_2$O interactions. The number of discernible peaks increases from two in pure CO$_2$ to three in CO$_2$-water mixtures. The different CO$_2$ bands were assigned to $ nu $ (2351 cm$^ $, 4.25 mu m) caused by CO$_2$ dangling bonds (CO$_2$ found in pores or cracks) and $ nu $ (2345 cm$^ $, 4.26 mu m) due to CO$_2$ segregated in water ice, whereas $ nu $ (2341 cm$^ $, 4.27 mu m) is due to CO$_2$ molecules embedded in water ice. The JWST NIRSpec CO$_2$ spectra for Ganymede and for Europa can be fitted with two Gaussians attributed to $ nu $ and $ nu $. For Europa, $ nu $ is located at lower wavelengths due to a lower temperature. The Ganymede data reveal latitudinal variations in CO$_2$ bands, with $ nu $ dominating in the pole and $ nu $ prevalent in other regions. This shows that CO$_2$ is embedded in water ice at the poles and it is present in pores or cracks in other regions. Ganymede longitudinal spectra reveal an increase of the CO$_2$ $ nu $ band throughout the day, possibly due to ice cracks or pores caused by large temperature fluctuations.

Interfacial modulation of hollow ZnS-SnS2 microboxs by Ti3C2Tx MXene to construct three-dimensional hybrid anodes for lithium-ion batteries with ultra high stability at low temperature

Metal sulfides exhibit obvious volume expansion due to the inherent poor conductivity and large temperature fluctuations, leading to reduced storage capacity. Herein, an electrostatic self-assembly strategy was proposed to fabricate a three-dimensional (3D) polyaniline (PANI) encapsulated hollow ZnS-SnS2 (H-ZSS) heterojunction confined on Ti3C2Tx MXene nanosheets (H-ZnS-SnS2@MXene@PANI, denoted as H-ZSSMP), which exhibits remarkable reversible capacity and cyclic stability (520.3 mAh/g at 2 A/g after 1000 cycles) at room temperature. Additionally, specific capacity can stabilized at 362.5 mAh/g for 250 cycles at −20 °C. A full cell with the configuration of H-ZSSMP//lithium iron phosphate (LiFePO4) can retain a satisfactory reversible capacity of 424.7 mAh/g after 100 cycles at 0.1 C. Theory calculations confirm heterogeneous interface can accelerate the transfer of ions through the interfacial regulation effect of MXene on H-ZSS. Our work provides a simple strategy to improve the capacity and stability of lithium-ion batteries (LIBs), as well as the new applications of MXene and bimetallic sulfides as anode materials, which will facilitate the development of MXene based composites for energy storage.

Modelling fuel oil transformation on geographically different seacoasts and assessing their self-cleansing capacity.

The present paper considers the results of long-term (up to 17years) in situ and laboratory research carried out on oiled French, Spanish, and Russian seacoasts. The objective of this research is to quantify the influence of geographical factors on the rates of natural transformation of the heavy fuel oil stranded ashore and to develop an empirical statistical model in order to evaluate the self-cleansing capacity of the coastal environment. In a number of field campaigns, 363 samples of weathered oil slicks and tar balls have been collected and analysed with the use of thin-layer chromatography combined with optical and gravimetric methods. The results obtained have been subjected to multiple nonlinear regression analyses. It has been shown that heavy fuel oil natural attenuation is more active in continental or estuarine environments influenced by nutrient-rich freshwater runoff and characterised by a higher number of sunny days, solar irradiation, and large temperature fluctuations. On the oceanic coasts, especially in sectors with low hydrodynamic energy, these processes take more time. The resulting model allows for the identification and mapping of the most vulnerable seacoasts, characterised by a low potential to degrade oil pollution. This information may be used in the contingency plans in order to optimise clean-up techniques and associated costs.

Bilateral passive thermal management for dynamical temperature regulation

Space heating and cooling of buildings account for ∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim $$\\end{document} 30% of energy consumed globally. As a result, efforts to reduce the carbon footprint associated with building temperature regulation are crucial to achieving sustainability goals. Passive radiative cooling and sun heating are two promising innovations that can help reduce the energy consumption associated with building temperature regulation. However, these methods are constrained by factors such as climate zones and seasonal changes. In this work, we demonstrate numerically that bilateral photonic metamaterials enabled by vanadium dioxide (VO2) nanoparticles embedded into polyethylene nanogratings can achieve dynamically modulate solar absorptance at one side in winter and achieve radiative cooling on another side. In cold weather, the solar absorptance of this metastructure can change from 0.93 to 0.2 at a critical temperature when VO2 changes from a metallic to an insulating state. This metastructure consists of broadband transparent polyethylene (PE) gratings on the reflective silver (Ag) gratings with the same period and filling ratio. These gratings are deposited on top of the Polydimethylsiloxane (PDMS) thin film. The VO2 nanoparticles enable dynamic solar absorptance modulation for winter space heating, while the PDMS with strong infrared emittance derived from molecular vibrations over the atmospheric window for summer radiative cooling. Temperature response simulations validate that this bilateral design achieves   6 °C subambient temperature drop at noontime in the summer and stabilizes its temperature around 22 °C during the daytime in the winter. This passive dynamical thermal regulation technique can be deployed for energy-saving targets of buildings, vehicles, and greenhouses in areas with large temperature fluctuations.

Biparental incubation behaviour under temperature extremes in sandbank nesting black skimmers.

Birds nesting on riverine beaches are exposed to large temperature fluctuations, while changing water levels pose flooding risks. We used miniature temperature loggers (iButtons®) placed in nests and on the beach surface combined with time-lapse photography to study incubation behaviour in the black skimmer (Rynchops niger) on the Manu River, Peru. Since the species exhibits sexual size dimorphism, we could identify partner switches in images and the contribution to incubation effort by each pair member. Results of the study documented that nest temperature was less affected by ambient temperature and fluctuated less than the surroundings. Despite shorter incubation bouts at midday, black skimmers maintained a close to constant presence at the nest by more frequent nest exchanges. In fact, while female black skimmers generally incubated more and for longer than males, pairs shared incubation most consistently during the hottest part of the day. Incubation probability decreased around dusk, a peak foraging time for the species and a time when beach temperature overlapped with nest temperature. A biparental incubation strategy across the diel cycle appears to allow black skimmers breeding at the Manu River to incubate in challenging thermal conditions, but further studies are needed to determine proximity to thermal limits.

Heat shocks during egg incubation led to developmental, morphological, and behavioral differences in Arctic charr (Salvelinus alpinus).

Temperature variation is affecting fish biodiversity worldwide, causing changes in geographic distribution, phenotypic structure, and even species extinction. Incubation is a critical stage for stenothermic species, which are vulnerable to large temperature fluctuations, and its effects on the phenotype at later developmental stages are understudied, despite the fact that the phenotype being essential for organism ecology and evolution. In this study, we tested the effects of heat shocks during the embryonic period on the phenotype of Arctic charr (Salvelinus alpinus). We repeatedly quantified multiple phenotypic traits, including morphology, development, and behavior, over a period of 4 months, from hatching to juvenile stage in individuals that had experienced heat shocks (+ 5°C on 24 h, seven times) during their embryonic stage and those that had not. We found that heat shocks led to smaller body size at hatching and a lower sociability. Interestingly, these effects weakened throughout the development of individuals and even reversed in the case of body size. We also found an accelerated growth rate and a higher body condition in the presence of heat shocks. Our study provides evidence that heat shocks experienced during incubation can have long-lasting effects on an individual's phenotype. This highlights the importance of the incubation phase for the development of ectothermic organisms and suggests that temperature fluctuations may have significant ecological and evolutionary implications for Arctic charr. Given the predicted increase in extreme events and the unpredictability of temperature fluctuations, it is critical to further investigate their effects on development by examining fluctuations that vary in frequency and intensity.

Successive responses of three coral holobiont components (coral hosts, symbiotic algae, and bacteria) to daily temperature fluctuations

Corals and their associated microbiota form a “holobiont,” which includes symbiotic algae and other associated microbiota dominated by bacteria. The composition of holobiont is influenced by various environmental factors, such as increasing sea water temperatures. Previous studies of the effects of temperature changes on coral physiology and associated bacterial communities have been conducted based on stable water temperatures set by mean temperatures, or by slowly increasing/decreasing temperatures. However, the daily temperature fluctuations that corals experience in nature are not stable. The current understanding of the effects of large daily temperature fluctuations on coral and associated bacterial community dynamics is limited. Hence, we conducted a four-week tank experiment using different large daily temperature fluctuations (±5 °C and ±7 °C) accompanied by continuous warming conditions (26 °C to 29 °C) to investigate the effects on two common reef-building corals, Stylophora pistillata and Pocillopora acuta. During the experiment, the activity of coral host catalase and superoxide dismutase were measured, the photosynthetic ability of symbiotic algae was recorded, and the variation in bacterial communities was analyzed using the V6-V8 region of 16S rDNA. According to the results, different parts of the holobionts of two coral species exhibited varying response rates to the continuous warming conditions and diurnal temperature fluctuations. Additionally, it was found that diurnal temperature fluctuations may mitigate the heat stress on the host and reduce the changes in bacterial response to warming. Therefore, it is suggested that the holobionts of different coral species may adopt different adaptation and survival strategies in response to diurnal temperature fluctuations and warming. Finally, based on the response of these two coral species under the conditions of diurnal temperature fluctuations and continuous warming, Acinetobacter and Rhodobacteraceae were identified as potential indicator coral-associated bacteria. This is the first study to investigate the tripartite dynamic response of coral, symbiotic algae and bacteria to daily temperature fluctuations.

A TEMPERATURE PRE-RECTIFIER WITH CONTINUOUS HEAT STORAGE AND RELEASE FOR WASTE HEAT RECOVERY FROM PERIODIC FLUE GAS

Flue gas from periodic furnaces with large temperature fluctuation is difficult to be recovered by regular heat exchangers. To recover that unstable waste heat, a temperature pre-rectifier (TPR) with honeycombed structure is developed to smooth down the temperature fluctuation by continuous heat storing and heat releasing. A three-dimensional model of TPR is constructed to analyze the heat transfer process. Temperature rectification rate η is defined to quantify the smoothing-down effect of TPR on temperature fluctuation. The relative size <i>s</i>* as the ratio of hole size to inner wall thickness (i.e., <i>s</i>* = <i>s/δ</i>), can be used to measure the capacity of heat release compared to that of heat storage. The quantity η reaches the highest value when the relative size <i>s</i>* is 1.0, and is increased with dimensionless length <i>l</i>*. When <i>s</i>* = 1.0, η firstly rises and then drops with the increment of <i>s</i>. The peak value of η can be achieved by an optimized hole size <i>s</i><sub>opt</sub>. The <i>s</i><sub>opt</sub> value increases exponentially with the inlet temperature fluctuation intensity. The TPR with segmented structure can enhance n with relatively short length. The three-segment structure with a proportion of 0.18:0.33:0.49 makes η > 0.947, which is recommended for application. Industrial experiments showed that the temperature fluctuation of flue gas can be rectified from 568-1709 K to 1089-1174 K (η = 0.926) by TPR, which verified that the TPR is an effective method for waste heat recovery from periodic flue gas.

Preparation of V2O5 thin films on AA6061 alloy using thermal evaporation

Spacecrafts often operate in severe environments with large exterior temperature fluctuations varying from −150 °C to +150 °C. Spacecraft internal parts work at their optimal efficiency between a range of temperatures, most likely between −10° C to 40 °C, beyond which they suffer damage. Consequently, good thermal management of spacecraft is required. The current technologies may become inadequate in the future owing to stringent requirements of micro- and nanosatellites, which entail the necessity of smaller and smarter thermal control subsystems. Traditional thermal technologies such as heaters, thermostats, heat pipes, coolers, and louvers will almost probably not be adequate to satisfy the requirements, since they are typically heavy and consume more electricity. Hence, Variable emittance coatings, which may modify the effective infrared emissivity and hence the radiative heat transfer rate, will be the inevitable potential choice for flexible or intelligent thermal management of spacecraft. Among all vanadium oxides, VO2 has been shown to exhibit a reversible phase shift at positive temperatures at 68 °C. This phase shift modifies its thermo-optical properties. Thermal evaporation was used to create V2O5 thin films on an AA6061 substrate, and subsequent reduction with N2 gas resulted in the creation of VO2. SEM, EDAX, and XRD were used to characterize the materials.

A self-driven solar air heater integrated with a thermal energy storage unit: Design and experiment study

The Self-driven solar air heater (SDSAH) can operate independently without reliance on an external power grid through the incorporation of photovoltaic (PV) panels, however it is still subject to intermittent operation and large temperature fluctuations. In this study, a novel SDSAH integrated with a thermal energy storage (TES) unit was proposed and the operational thermal and electrical performance of the SDSAH with TES unit were experimentally investigated. The results showed that the SDSAH could output heat continuously throughout the day (24 h) in a self-sustaining mode and automatically adjust the airflow rate according to solar irradiance. The overall thermal efficiency of this system averages at 52.73 % throughout the day. The introduction of the TES unit could lower the peak temperature of the outlet air by more than 9 K and improve the electrical efficiency of PV panels. However, due to heat loss at night, the whole-day thermal efficiency will be slightly lower than that of SDSAH without a TES unit. The energy payback time for this system was 42 months. This study offers new ideas and solutions for a distributed agricultural drying system.

Field investigation of non-uniform environment in a Venlo-type greenhouse in Yangling, China

Non-uniform environmental conditioning has established substantial energy-saving and conditioning effects in residential buildings, however, few studies on the technology applied in greenhouses have been conducted. Semi-enclosed greenhouse development is hindered by energy consumption. To better apply non-uniform environmental conditioning technology in greenhouses, it is necessary to investigate the non-uniform characteristics of field environment parameters. Therefore, spatial and temporal measurements of indoor temperature and relative humidity in a Venlo-type greenhouse in Yangling, China, were conducted on June 5–11, 2022. Temperature and humidity sensors were arranged in the greenhouse at 4.5 m intervals, in the canopy, cultivation, center, and root areas. Temperature and humidity measurement points on the greenhouse walls were selected. The measurement results showed large fluctuations in the indoor temperature and relative humidity over time. The difference between indoor and outdoor average temperatures ranged from -5–10 °C and temperatures unsuitable for tomato growth were identified, although some passive conditioning methods such as ventilation and water spraying were employed, which indicates the necessity of active heating and cooling. Based on the measured data, the nonuniformity coefficients of temperature and relative humidity in different directions in the greenhouse were calculated. A larger non-uniformity in the vertical direction was found compared to that in the horizontal direction. These results suggest the possibility of non-uniform environmental conditioning. A rough estimation of the energy consumption by the two different condition modes, namely zone-specific and overall conditioning, was made. A huge energy saving of 69.6 % by the zone-specific conditioning mode was revealed compared to the overall conditioning. This implies a huge advantage in energy efficiency by non-unform environmental conditioning technologies applied in greenhouses. The study provides useful data for understanding non-uniform environments in greenhouses and the application of non-uniform environmental conditioning technologies.

Modeling and numerical analysis of PID-controlled phase-change transpiration cooling

This paper innovatively introduces PID control to the phase-change transpiration cooling process and numerically investigates the multi-physics process of coupled control, flow, and heat transfer through mathematical modeling. Based on numerical simulations, the critical equal-amplitude oscillation characteristics in PID-controlled phase-change transpiration cooling, the PID tuning method for the cooling system's fast stabilization, and the applicability of PID tuning strategies at various control conditions are discussed. The discussions show that liquid phase change significantly influences the PID-controlled response process. The response process is prone to large temperature fluctuations and overshoots when the final phase change position is far from that in the corresponding open-loop process. In addition, the classical tuning parameters from the Ziegler-Nichols critical proportional tuning method are not fully applicable due to the significant heat transfer hysteresis in the liquid phase change and must be revised. After revision, the PID tuning strategy can contribute to excellent control consistency and reliability when the target temperature keeps away from the saturated temperature of the coolant or the feedback location moves within the superheated vapor area.

Hygrothermal and Economic Analysis of an Earth-Based Building Using In Situ Investigations and Artificial Neural Network Modeling for Normandy’s Climate Conditions

This paper investigates the in situ hygrothermal behavior of a cob prototype building equipped with multiple sensors for measuring temperature, relative humidity inside the building, and water content within its walls. The experimental results show that the earth-based prototype building presents interesting thermal insulation performance. Without any heating system, the indoor temperature was found to remain stable, near 20 °C, despite large fluctuations in the outdoor temperature. This study also illustrated the ability of cob to absorb and regulate indoor relative humidity. The use of a neural network model for predicting the hygrothermal behavior of the cob prototype building was an additional objective of this work. This latter was centered on investigating the indoor ambience and moisture content within the walls. In this sense, a long short-term memory model (LSTM) was developed and trained. The validation results revealed an excellent agreement between the model predictions and experimental data, with R2 values of 0.994 for the indoor air temperature, 0.960 for the relative humidity, and 0.973, 0.925, and 0.938 for the moisture content at three different depths in the building’s walls. These results indicate that the LSTM model is a promising approach for predicting the indoor ambience of an earth-based building, with potential applications in building automation and energy management. Finally, an economic discussion of the CobBauge system is presented.

Transcriptional and translational dynamics underlying heat shock response in the thermophilic crenarchaeon Sulfolobus acidocaldarius.

Heat shock response is the ability to respond adequately to sudden temperature increases that could be harmful for cellular survival and fitness. It is crucial for microorganisms living in volcanic hot springs that are characterized by high temperatures and large temperature fluctuations. In this study, we investigated how S. acidocaldarius, which grows optimally at 75°C, responds to heat shock by altering its gene expression and protein production processes. We shed light on which cellular processes are affected by heat shock and propose a hypothesis on underlying regulatory mechanisms. This work is not only relevant for the organism's lifestyle, but also with regard to its evolutionary status. Indeed, S. acidocaldarius belongs to the archaea, an ancient group of microbes that is more closely related to eukaryotes than to bacteria. Our study thus also contributes to a better understanding of the early evolution of heat shock response.

The effects of winter cold acclimation on acute and chronic cadmium bioaccumulation and toxicity in the banded killifish (Fundulus diaphanus)

Temperate freshwater fishes can experience large seasonal temperature fluctuations that could affect their exposure and sensitivity to trace metals. Yet, temperature effects are overlooked in ecotoxicology studies, especially for cold temperatures typical of the winter. In the present study, the effects of long-term cold acclimation on Cd bioaccumulation and toxicity were investigated in a freshwater fish, the banded killifish (Fundulus diaphanus). Killifish were acclimated to 14 °C or gradually cooled (2 °C/week) to 4 °C and cold acclimated for 6 weeks. Then, both acclimation groups were exposed to environmentally realistic waterborne Cd concentrations (0, 0.5 or 5 µg Cd L−1) for a further 28 d at their respective acclimation temperatures. Tissue metal bioaccumulation, fish survival, condition, and markers of oxidative and ionoregulation stress, were measured after 0, 2, 5 and 28 days of Cd exposure. Cadmium tissue accumulation increased over the exposure duration and was typically lower in cold-acclimated fish. In agreement with this lower bioaccumulation, fewer Cd toxic effects were observed in cold-acclimated fish. There was little evidence of a difference in intrinsic Cd sensitivity between 4 °C- and 14 °C-acclimated fish, as Cd toxicity appeared to closely follow Cd bioaccumulation. Our study suggests that current environmental water quality guidelines would be protective in the winter for the abundant and ecologically-important banded killifish.

Adaptation strategies of relatively high-latitude marginal reef corals in response to severe temperature fluctuations

The large seasonal temperature fluctuations caused by global warming and frequent marine heatwaves pose new challenges to survival of relatively high-latitude marginal reef corals. However, the adaptation strategies of high-latitude marginal corals are not fully understood. We employed integrated approach to investigate the response mechanism of hosts, Symbiodiniaceae, and symbiotic bacteria of marginal reef corals Acropora pruinosa and Pavona decussate in response to large seasonal temperature fluctuations. The coral holobiont maintained a high level of immunity to adapt to seasonal pressure by increasing Symbiodiniaceae energy supply. The symbiotic Symbiodiniaceae of two coral was dominated by C1 subgroup, and was stable across seasons. The α-diversity of symbiotic bacteria P. decussata and A. pruinosa in summer was higher than that in winter. The symbiotic bacterial community of two coral reorganized during different seasons. Scleractinian corals improve adaptability to seasonal stress by increasing energy supply to maintain high levels of immunity, increasing symbiotic bacterial α-diversity, and changing dominant bacteria. This study demonstrates the adaptation strategies of marginal reef corals to seasonal temperature fluctuations and provides novel insights into the study of the adaptation of corals and relatively high-latitude coral refuges in the context of global warming and intensified marine heatwaves.

Confounding effects of snow cover on remotely sensed vegetation indices of evergreen and deciduous trees: An experimental study.

Located at northern latitudes and subject to large seasonal temperature fluctuations, boreal forests are sensitive to the changing climate, with evidence for both increasing and decreasing productivity, depending upon conditions. Optical remote sensing of vegetation indices based on spectral reflectance offers a means of monitoring vegetation photosynthetic activity and provides a powerful tool for observing how boreal forests respond to changing environmental conditions. Reflectance-based remotely sensed optical signals at northern latitude or high-altitude regions are readily confounded by snow coverage, hampering applications of satellite-based vegetation indices in tracking vegetation productivity at large scales. Unraveling the effects of snow can be challenging from satellite data, particularly when validation data are lacking. In this study, we established an experimental system in Alberta, Canada including six boreal tree species, both evergreen and deciduous, to evaluate the confounding effects of snow on three vegetation indices: the normalized difference vegetation index (NDVI), the photochemical reflectance index (PRI), and the chlorophyll/carotenoid index (CCI), all used in tracking vegetation productivity for boreal forests. Our results revealed substantial impacts of snow on canopy reflectance and vegetation indices, expressed as increased albedo, decreased NDVI values and increased PRI and CCI values. These effects varied among species and functional groups (evergreen and deciduous) and different vegetation indices were affected differently, indicating contradictory, confounding effects of snow on these indices. In addition to snow effects, we evaluated the contribution of deciduous trees to vegetation indices in mixed stands of evergreen and deciduous species, which contribute to the observed relationship between greenness-based indices and ecosystem productivity of many evergreen-dominated forests that contain a deciduous component. Our results demonstrate confounding and interacting effects of snow and vegetation type on vegetation indices and illustrate the importance of explicitly considering snow effects in any global-scale photosynthesis monitoring efforts using remotely sensed vegetation indices.

Active junction temperature control of IGBTs for electric vehicle drive system based on hybrid control strategy

Junction temperature swing is the most important factor to induce the IGBTs failure due to the associated internal temperature gradient acting on the mismatch of coefficients of thermal expansion between adjacent layers and internal temperature gradients, and smoothing the junction temperature fluctuation is a valid way to prolong the lifespan of IGBT modules. This paper investigates the dependency of the junction temperature fluctuation smoothing effect on the stator current and switching frequency, and presents a hybrid control strategy to smooth the junction temperature swing. Depending on the heating up or cooling down stages of IGBTs, the proposed strategy adjusts the stator current and switching frequency respectively. For simulation, Urban dynamometer driving schedule (UDDS) for the VEH_SMCAR model in ADVISOR is used to verify the effectiveness, where the evaluated result shows that the proposed method can effectively reduce the number of the large junction temperature fluctuation cycles and the life-span increases by 90 %. Meanwhile, the experimental results also validate the effectiveness of the proposed hybrid control strategy in smoothing junction temperature fluctuation.

Cosmic-ray driven galactic winds from the warm interstellar medium

ABSTRACT We study the properties of cosmic-ray (CR) driven galactic winds from the warm interstellar medium using idealized spherically symmetric time-dependent simulations. The key ingredients in the model are radiative cooling and CR-streaming-mediated heating of the gas. Cooling and CR heating balance near the base of the wind, but this equilibrium is thermally unstable, leading to a multiphase wind with large fluctuations in density and temperature. In most of our simulations, the heating eventually overwhelms cooling, leading to a rapid increase in temperature and a thermally driven wind; the exception to this is in galaxies with the shallowest potentials, which produce nearly isothermal $T \approx 10^4\,$ K winds driven by CR pressure. Many of the time-averaged wind solutions found here have a remarkable critical point structure, with two critical points. Scaled to real galaxies, we find mass outflow rates $\dot{M}$ somewhat larger than the observed star-formation rate in low-mass galaxies, and an approximately ‘energy-like’ scaling $\dot{M} \propto v_{\rm esc}^{-2}$. The winds accelerate slowly and reach asymptotic wind speeds of only ∼0.4vesc. The total wind power is $\sim 1~{{\ \rm per\ cent}}$ of the power from supernovae, suggesting inefficient preventive CR feedback for the physical conditions modelled here. We predict significant spatially extended emission and absorption lines from 104–105.5 K gas; this may correspond to extraplanar diffuse ionized gas seen in star-forming galaxies.

High-Resolution Two-Dimensional Numerical Simulation of n-Heptane/Air Autoignition Under the Influence of Temperature Fluctuation

ABSTRACT High-resolution two-dimensional numerical simulations are performed to investigate n-heptane/air autoignition process under different initial temperatures with varied levels of temperature fluctuations. It is found that temperature fluctuation has an important impact on the autoignition process, and its effects depend on the initial mean temperature. When is located at the upper turning point of the negative temperature coefficient (NTC) regime, as the temperature fluctuation increases, the autoignition mode evolves from a single-stage ignition mode controlled by high-temperature chemistry (HTC) to a mode characterized by the coexisting of multi-stage and single-stage ignition. Both the first-stage heat release and ignition delay increase, but the overall heat release and the total ignition delay decrease. In the presence of a large temperature fluctuation, the low-temperature chemistry (LTC), and HTC reactions, single-stage and two-stage ignitions could coexist in the domain. Chemical explosive mode and sensitivity analyses are performed to identify the reaction mode and the key element reactions in the mutli-stage autoignition process. The temperature fluctuation has a significant promotion effect on the overall ignition except when is located at the lower turning point of the NTC regime. Overall, the NTC phenomenon is weakened under the influence of temperature fluctuation, approaching to zero temperature coefficient (ZTC) phenomenon.