Effects Of Different Ambient Temperatures Research Articles

Relationship between Ambient Temperature and Reasonable Heat Dissipation Coefficient of Mass Concrete Pouring Blocks.

In engineering practice, similar surface insulation measures are typically applied to different parts of mass concrete surfaces. However, this can lead to cracking at the edges of the concrete surface or the wastage of insulation materials. In comparison to flat surfaces, the edges of mass concrete structures dissipate heat more rapidly, leading to more pronounced stress concentration phenomena. Therefore, reinforced insulation measures are necessary. To reduce energy consumption and enhance overall insulation effectiveness, it is essential to study the specific insulation requirements of both the flat surfaces and edges of concrete separately and implement targeted surface insulation measures. Taking the bridge abutment planned for pouring in Nanjing City as the research object, this study established a finite element model to explore the effects of different ambient temperatures and different surface heat dissipation coefficients on the early-age temperature and stress fields of different parts of the abutment's surface. Based on simulation results, reasonable heat dissipation coefficients that meet the requirements for crack prevention on both the structure's plane and edges under different ambient temperatures were obtained. The results indicate that under the same conditions, the reasonable heat dissipation coefficient at the edges was smaller than that on the flat surfaces, indicating the need for stronger insulation measures at the edges. Finally, mathematical models correlating ambient temperature with reasonable heat dissipation coefficients for the structure's plane and edges at these temperatures were established, with high data correlation and determination coefficients (R2) of 0.95 and 0.92. The mathematical models were validated, and the results from finite element calculations were found to be consistent with those from the mathematical models, validating the accuracy of the mathematical models. The conclusions drawn can provide references for the insulation of similar engineering concrete planes and edges.

Ethanol Inhomogeneous Lean Combustion Under Different Ambient Temperatures and Pressures with Hydrogen Enrichment

ABSTRACT The effects of different ambient temperatures and pressures on the combustion of hydrogen-enriched liquid ethanol spray were studied in a constant-volume vessel, using experimental and numerical methods. The inhomogeneous combustion experiment was conducted under ultra-lean conditions at an overall equivalence ratio of 0.3 (33% spray ethanol/67% premixed hydrogen). The spray and flame images and combustion pressures were obtained. The spray simulation models used were the RANS k-ε turbulence model, KH-RT model, and wall film interaction model. The experimental results showed that the inhomogeneous combustion of the liquid ethanol spray can be divided into two stages: a rapid-burning and a slow-burning stage. The slow-burning stage was sensitive to changes in ambient temperature and pressure. Combustion duration decreased with elevated pressure and declined temperature. Under low pressure and medium temperature conditions, the flame reached its fastest propagation speed. The simulation results showed that the fuel concentration and concentration gradient around the ignition position are the key factors that affect inhomogeneous lean combustion. When the equivalence ratio was over 0.8 around the ignition position and the gradient of the equivalence ratio increased no less than 0.1/mm, the optimal combustion characteristics were achieved.

A data-driven performance analysis and prediction method for electric vehicle cabin thermal management system

Urban conditions and passenger behaviors primarily affect the performance of the electric vehicle (EV) cabin thermal management system (CTMS). The systematic analysis and accurate prediction of performance variations are crucial for the holistic optimization of the system. This study evaluated the effect of different ambient temperatures, solar radiations, driving patterns, and preset temperatures in Beijing, China. Energy analysis, exergy analysis, and the adaptive predictive mean vote method were employed to comprehensively analyze the performance of air conditioning (AC) system and cabin thermal comfort. A support vector machine model based on the multi-improved snake optimizer (MISO-SVM) was proposed to predict the CTMS performance. Chaotic mapping, subtraction-average-based optimizer, and lens imaging reverse learning strategy were applied to enhance the optimization capabilities of the traditional snake optimizer. A CTMS model was developed and validated to facilitate analysis and dataset acquisition. The results indicate that the energy consumption increases dramatically with elevated ambient temperatures (9.27 times increase from 26 °C to 40 °C) and solar radiation (11.42 times increase from 0 to 1200 W/m2). Conversely, high-speed driving patterns and higher preset temperatures (16 °C to 26 °C) are associated with improved AC system performance, leading to a reduction in energy consumption by up to 79.59 %. Moreover, the MISO-SVM model outperforms the traditional prediction models regarding CTMS performance prediction efficiency. The optimized MISO algorithm reduces the average convergence iterations by 20.59 % and achieves an average reduction of 18.92 % in fitness values. Across diverse prediction tasks, the MISO-SVM consistently maintains R2 above 0.99 and the lowest mean squared error. This study may provide new insights into the performance analysis and prediction of CTMS in EVs.

Numerical and experimental research on electromagnetic-thermal and leakage defects characteristics of the high voltage cable terminal

Thermal and insulation performance of the High Voltage Cable Terminal (HVCT) could effectively improve the reliability and economy of power energy transmission. In this paper, a numerical model of the electromagnetic heat flow field was proposed to analyze the heat transfer and temperature characteristics of HVCT under oil leakage defects. This model was the first validated using operation data from the actual equipment and the relative error was less than 1.51%. The effects of oil leakage fault on the global and local temperature distribution of the HVCT were then investigated under different load currents. In addition, the local temperature rise effect of different ambient temperatures on the HVCT oil leakage defect was also considered. Finally, combined with reference indicators such as oil level, temperature, and temperature gradient, a qualitative and quantitative evaluation of the oil leakage fault of HVCT was performed. The results showed that the temperature of the core, surface, and their maximum temperature gradient were linearly related to the ambient temperature. However, the temperature of the core at the oil leak exceeded the normal temperature by up to 7.2 °C with 1000A load current, and the temperature gradient change reaches 681.3 °C/m, which indicated that the convection heat dissipation effect of the oil-deficient part was poor, and the heat accumulates near the cable core. Therefore, the numerical model and analytical results presented in this paper provided an important method for online temperature monitoring and fault analysis of HVCTs.

Cold exposure protects against medial arterial calcification development via autophagy

Medial arterial calcification (MAC), a systemic vascular disease different from atherosclerosis, is associated with an increased incidence of cardiovascular events. Several studies have demonstrated that ambient temperature is one of the most important factors affecting cardiovascular events. However, there has been limited research on the effect of different ambient temperatures on MAC. In the present study, we showed that cold temperature exposure (CT) in mice slowed down the formation of vitamin D (VD)-induced vascular calcification compared with room temperature exposure (RT). To investigate the mechanism involved, we isolated plasma-derived exosomes from mice subjected to CT or RT for 30 days (CT-Exo or RT-Exo, respectively). Compared with RT-Exo, CT-Exo remarkably alleviated the calcification/senescence formation of vascular smooth muscle cells (VSMCs) and promoted autophagy by activating the phosphorylation of AMP-activated protein kinase (p-AMPK) and inhibiting phosphorylation of mammalian target of rapamycin (p-mTOR). At the same time, CT-Exo promoted autophagy in β-glycerophosphate (β-GP)-induced VSMCs. The number of autophagosomes and the expression of autophagy-related proteins ATG5 and LC3B increased, while the expression of p62 decreased. Based on a microRNA chip microarray assay and real-time polymerase chain reaction, miR-320a-3p was highly enriched in CT-Exo as well as thoracic aortic vessels in CT mice. miR-320a-3p downregulation in CT-Exo using AntagomiR-320a-3p inhibited autophagy and blunted its anti-calcification protective effect on VSMCs. Moreover, we identified that programmed cell death 4 (PDCD4) is a target of miR-320a-3p, and silencing PDCD4 increased autophagy and decreased calcification in VSMCs. Treatment with CT-Exo alleviated the formation of MAC in VD-treated mice, while these effects were partially reversed by GW4869. Furthermore, the anti-arterial calcification protective effects of CT-Exo were largely abolished by AntagomiR-320a-3p in VD-induced mice. In summary, we have highlighted that prolonged cold may be a good way to reduce the incidence of MAC. Specifically, miR-320a-3p from CT-Exo could protect against the initiation and progression of MAC via the AMPK/mTOR autophagy pathway.Graphic

Incremental capacity analysis (dQ/dV) as a tool for analysing the effect of ambient temperature and mechanical clamping on degradation

This work presents a comprehensive degradation study of two types of large lithium-ion pouch cells; 26 NMC532/Graphite (64 Ah) and 9 NMC433/Graphite (31 Ah) pouch cells. The cells were degraded under different cycling conditions and periodically characterized at room temperature. Specifically, the effect of different ambient temperatures and constraining the cells by clamping was studied. Incremental capacity analysis is an in situ, non-invasive characterization technique that allows the identification of battery degradation modes, and is a technique that does not require additional and advanced equipment. Therefore, in this study we also look into applying the analysis technique on an existing data set. This is done by combining incremental capacity analysis on a qualitative level with the tracking of features of interest in the incremental capacity curve as a function of State of Health and utilizing the simulation of different degradation modes for a more in-depth analysis. We combine simulation and experimental incremental capacity analysis with conclusions from capacity loss and resistance changes with a focus on understanding the benefit and limitations of the incremental capacity analysis for large cells. This is important, as incremental capacity analysis is a relatively fast analysis to qualify large commercial batteries for 2nd life applications. Specifically in this study, we found that degradation and capacity loss do not always correlate. For the 64 Ah Cells cycled at 15 °C and 25 °C, the rate of capacity loss appeared to be similar, although the degradation modes and mechanisms are found to be very different. The clamping was the most important factor for impeding degradation. The 31 Ah Cell cycled at low temperatures showed a very poor cycling performance, where the incremental capacity analysis revealed that Loss of Lithium Inventory from fast and irreversible plating was responsible.

Effect of Different Ambient Temperatures on Reproductive Outcome and Stress Level of Lactating Females in Two Mouse Strains.

Simple SummaryThe optimal temperature for laboratory mice has been under discussion for some time. Current standard temperature is 20 °C–24 °C but it has been suggested to elevate the standard to 30 °C, which is the thermoneutral zone for mice. In this study, the effect of different cage temperatures (20 °C, 25 °C, 30 °C) on reproduction and stress hormone metabolite excretion was evaluated in lactating females of two commonly used mouse strains. Pup loss was higher, and weights of mothers and pups were reduced at 30 °C compared to the lower temperatures. In addition, pups showed increased tail length at weaning under the high temperature (30 °C). There was no difference in stress hormone metabolite excretion in mice between temperature groups. We could not show any detrimental effects of the lower or higher cage temperature on stress hormone metabolite excretion, but found decreased reproductive outcome under the higher temperature.Ambient temperature is an important non-biotic environmental factor influencing immunological and oncological parameters in laboratory mice. It is under discussion which temperature is more appropriate and whether the commonly used room temperature in rodent facilities of about 21 °C represents a chronic cold stress or the 30 °C of the thermoneutral zone constitutes heat stress for the animals. In this study, we selected the physiological challenging period of lactation to investigate the influence of a cage temperature of 20 °C, 25 °C, and 30 °C, respectively, on reproductive performance and stress hormone levels in two frequently used mouse strains. We found that B6D2F1 hybrid mothers weaned more pups compared to C57BL/6N mothers, and that the number of weaned pups was reduced when mothers of both strains were kept at 30 °C. Furthermore, at 30 °C, mothers and pups showed reduced body weight at weaning and offspring had longer tails. Despite pronounced temperature effects on reproductive parameters, we did not find any temperature effects on adrenocortical activity in breeding and control mice. Independent of the ambient temperature, however, we found that females raising pups showed elevated levels of faecal corticosterone metabolites (FCMs) compared to controls. Peak levels of stress hormone metabolites were measured around birth and during the third week of lactation. Our results provide no evidence of an advantage for keeping lactating mice in ambient temperatures near the thermoneutral zone. In contrast, we found that a 30 °C cage temperature during lactation reduced body mass in females and their offspring and declined female reproductive performance.

Experimental Study on Shear Strengths of Ice-Roof Interface Aiming the Study of Roof Snow Sliding

Snow sliding of roofs is a threat to the structural safety of roof structures by causing a surcharge of local snow load on the lower roof and may pose a serious threat to pedestrians and vehicles on the ground. Therefore, it is of great significance to study the mechanism of snow sliding on roofs. Under the action of ambient temperature, solar radiation, internal heating of the building, etc., the bottom layer of roof snow is often presented in the form of porous ice after a complicated phase transition of the snow particles. Under this circumstance, the interface between roof snow and the roof can be seen as the contact between porous ice and the roofing material. In order to investigate the initialization of roof snow sliding from the material point of view, the shear performance of the interface between different roofing materials and ice with different porosities was carried out in this study. The effects of different ambient temperatures (−4, −6, and −8°C), different normal stress (0, 50, and 100 kPa), and different ice porosities (represented by the contact area ratio of 1.0, 0.8, and 0.6) on this shear performance were analyzed by direct shear tests. The test results showed that the shear failure between the ice and the roofing material was brittle, and the interface shear strength was affected by the ambient temperature, normal stress, contact area ratio, as well as the material type: the strength increases with the decrease of ambient temperature, the increase of normal stress, the increase of contact area ratio, and the increase of surface roughness of the material. Based on the test results, a quantitative relationship between the interface shear strength and the related factors was given in the article, which provides a useful reference for future experimental or simulation studies on roof snow sliding.

Viscoelastic-Thermodynamic Model and Crack Propagation in Asphalt Concrete Pavement

Asphalt concrete pavement has a wide range of applications in the construction of high-grade highways. Asphalt concrete pavement has elastic properties, and its viscoelasticity and viscoplasticity are obviously affected by temperature. To determine whether a structure can continue to be used safely, it is most important to determine whether microscopic or macroscopic cracks present in the structure continue to propagate and cause structural failure. The purpose of this study was to study the effects of different ambient temperatures and mobile vehicles on the stress around the crack tip and the propagation path of different types of asphalt pavements. Based on the theory of fracture mechanics and viscoelasticity, this work studies the problem of crack propagation from a macroscopic perspective. It proposes to use the finite element method to analyze the crack problem in the pavement structure. With the help of ABAQUS software, a curved beam model with cracks was established for calculation, and moving loads and ambient temperature fields were added for analysis. The experimental results in this study show that with the decrease in the ambient temperature, the stress at the crack tip increases continuously. As the analysis time increases, the stress also increases. When the crack is smaller, the stress value at the tip is larger. When a = 15 mm, the stress value at the crack tip is the largest. However, when a = 20 mm and a = 25 mm, the stress at the crack tip is significantly reduced. It shows that the crack is easier to crack when the crack value is smaller. After the crack has grown to a certain length, the growth rate will slow down.

Development of Chrysomya albiceps (Wiedemann, 1819) (Diptera: Calliphoridae) from the Jazan region of Southwest Saudi Arabia under different laboratory temperatures: applications in forensic entomology

BackgroundChrysomya albiceps (Wiedemann, 1819) (blowflies), family Calliphoridae, is important in forensic entomology, where the minimum and maximum postmortem intervals (PMI) are estimated on the basis of the developmental stages of Diptera larvae that consume dead tissue. The present study was designed to estimate the effects of different ambient temperatures (20, 25, and 30 °C) under controlled laboratory conditions on the developmental stages of C. albiceps from the Jazan region, Saudi Arabia.ResultsThe present study showed that the larval body weight and length were significantly increased when larvae were reared at 30 °C compared with corresponding values at 24 h, 48 h, and 72 h at rearing temperatures of 20 °C and 25 °C; however, the weight and length were significantly decreased compared with corresponding values at 96 h at 20 °C and 25 °C. The pupation time was inversely related to the rearing temperature, occurring at 144, 124, and 120 h at rearing temperatures of 20 °C, 25 °C, and 30 °C, respectively. The pupal weight and length were significantly increased in larvae reared at 30 °C compared with those reared at 20 °C and 25 °C. At 20 °C, 25 °C, and 30 °C, larval durations of 5.00, 5.00, and 4.00 days were recorded, respectively. Pupae and adults showed gradual decreases in life stage durations, at 6.00, 5.30, and 4.80 days in pupae and 20.00, 18.70, and 16.90 days in adults, with increasing rearing temperatures. Average adult longevity at 30 °C (194.40 h) was significantly less than adult longevity at 20 °C (216.00 h) and 25 °C (204.60 h). The results showed an inverse relation between durations of developmental stages and rearing temperatures.ConclusionsInsect laboratory colonization for the determination of biological characteristics of insects is economically viable for forensic entomology and as a technique for evaluating insect evidence.

Effects of Different Ambient Temperatures on Caecal Microbial Composition in Broilers.

Short-term or acute temperature stress affect the immune responses and alters the gut microbiota of broilers, but the influences of long-term temperature stress on stress biomarkers and the intestinal microbiota remains largely unknown. Therefore, we examined the effect of three long-term ambient temperatures (high (HC), medium (MC), and low (LC) temperature groups) on the gene expression of broilers’ heat shock proteins (Hsps) and inflammation – related genes, as well as the caecal microbial composition. The results revealed that Hsp70 and Hsp90 levels in HC group significantly increased, and levels of Hsp70, Hsp90, IL-6, TNF-α, and NFKB1 in LC group were significantly higher than in MC group (p < 0.05). In comparison with the MC group, the proportion of Firmicutes increased in HC and LC groups, while that of Bacteroidetes decreased in LC group at phylum level (p < 0.05). At genus level, the proportion of Escherichia/Shigella, Phascolarctobacterium, Parabacteroides,and Enterococcus increased in HC group; the fraction of Faecalibacterium was higher in LC group; and the percentage of Barnesiella and Alistipes decreased in both HC and LC groups (p < 0.05). Functional analysis based on communities’ phylogenetic investigation revealed that the pathways involved in environmental information processing and metabolism were enriched in the HC group. Those involved in cellular processes and signaling, metabolism, and gene regulation were enriched in LC group. Hence, we conclude that the long-term temperature stress can greatly alter the intestinal microbial communities in broilers and may further affect the host’s immunity and health.

The Impact of Temperature and Humidity on the Performance and Physiology of Laying Hens.

Simple SummaryThe present study investigated whether the temperature-humidity index (THI) influences the production parameters and physiology of laying hens. Two environmental conditions combining high temperature with low relative humidity (TLHH75) or vice versa (THHL75), with the same THI value (75), were considered. The same THI value indicated equal thermal stress for laying hens. Neither TLHH75 nor THHL75 affected laying performance, including egg production, egg weight, and egg mass, feed intake, feed conversion ratio, plasma biochemical parameters, and stress indicators. Our study suggests that laying hens exposed to the same THI values will receive similar thermal stresses. The results of this study will serve as a scientific basis for management decisions and handling laying hens under thermally challenging conditions.We investigated the effect of different ambient temperatures and relative humidity (RH) with the same temperature-humidity indices (THI) on laying performance, egg quality, heterophil to lymphocyte ratio (H/L ratio), corticosterone (CORT) concentration in blood, yolk, and albumen, and plasma biochemical parameters of laying hens. Commercial hens (Hy-Line Brown; n = 120), aged 60 weeks, were allocated to two environmental chambers. Laying hens were subjected to either one of two thermal treatments—26 °C and 70% RH (TLHH75) or 30 °C and 30% RH (THHL75) for 28 days—with the same THI of 75. Neither TLHH75 nor THHL75 affected laying performance, including egg production, egg weight, egg mass, feed intake, and feed conversion ratio (p > 0.05). Plasma biochemical parameters such as total cholesterol, high-density lipoprotein cholesterol, triglycerides, calcium, magnesium, and phosphorus were not altered by the environmental treatments (p > 0.05). As for stress indicators, both environmental regimes failed to affect blood H/L ratio and CORT levels in plasma, yolk, and albumen (p > 0.05), although albumen CORT levels were elevated (p < 0.05) in TLHH75 group at day 7. Hence, our study suggests that laying hens performed and responded similarly when exposed to either TLHH75 or THHL75 characterized by the same THI. These results can serve as a scientific basis for management decisions and handling laying hens under thermally challenging conditions.

Effect of ambient temperature on the productive and carcass traits of growing rabbits divergently selected for body fat content

Rabbits are particularly sensitive to heat stress which can affect productive performance, with rabbit breed/line possibly playing a role on the response to this condition. The study aimed at evaluating the effect of different ambient temperatures on the live performance and carcass traits of growing rabbits divergently selected for total body fat content. The two genetic lines (Lean and Fat) were selected based on the total body fat content estimated by computer tomography during five generations. From birth to slaughter (13 weeks of age), the rabbits were housed in two rooms where the temperature was controlled with air conditioners: in the control room the average ambient temperature was 20 °C and in the high temperature room it was 28 °C. After weaning (35 d), 60 Lean and 60 Fat rabbits/room were housed by two in wire-mesh cages and fed ad libitum with commercial pellets. The BW and feed intake (FI) were measured at 5, 7, 9, 11 and 13 weeks of age to calculate the daily weight gain (DWG) and feed conversion ratio (FCR). Mortality was recorded daily. At the end of the experiment, rabbits were slaughtered and carcass traits were measured. Mortality was independent of temperature and line. The temperature significantly influenced the FI, DWG, BW and the fat deposits: they were lower at higher ambient temperature. The effect of temperature differed according to the rabbits' total body fat content. At control temperature, the FI (165 vs 155 g/day; P < 0.05) and FCR (4.67 vs 4.31; P < 0.05) were higher in Fat rabbits, which also had more perirenal (36.2 vs 23.1 g; P < 0.05) and scapular fat (10.8 vs 7.1 g; P < 0.05). At high temperature, no differences in fat depots (14.5 vs 9.8 g; 5.3 vs 3.5 g) were found between the two lines. It can be concluded that temperature × genetic line interaction had an important role in productive and carcass traits, as the effect of temperature differs between Lean and Fat rabbits.

PCB thermal reliability characteristics analysis under ambient temperature

PCB is an important component for electronic devices – Mechanical connections and electrical transmission, thermal failure is its main failure mode, the heat flow analysis and thermal design is the basis and premise to improve thermal characteristics of PCBs. In this paper, based on the principles of fluid mechanics, using the finite volume method, the thermal characteristics of the PCB is modeled, and we obtain the maximum junction temperature of the PCB, PCB’s thermal distribution and effect of different ambient temperatures on the PCB thermal characteristics. The study provides a theoretical basis for the PCB thermal design.

Effect of temperature, resting time and brick dust (Horasan) on the rheological properties of hydraulic lime-based grouts

This paper aims to analyze the effect of different ambient temperatures on the time-dependent rheological properties of brick dust blended hydraulic lime-based grouts. Since there are limited studies about the rheological properties of lime-based grouts produced with brick dust (Horasan), the presence of this material (pozzolanic or non-pozzolanic) in the hydraulic lime-based grouts was investigated in terms of rheological parameters. Fluidity, volume stability, penetrability, water retention capacity and setting time of the grouts were determined. Moreover, the rheological measurements were performed with a rotational rheometer and yield stress and plastic viscosity of grouts were calculated from shear stress-shear rate curves. The common result of the methods reveals that the rheological properties of lime-based grouts were dramatically affected by temperature and resting time. Although the yield stress, plastic viscosity, and water retention capacity of lime-based grouts increased with the presence of brick dust, stable and homogenous grouts were obtained for a sufficient injectability. Finally, the temperatures between 20 °C to 30 °C were designated as threshold temperatures to apply the grout without the loss of fresh properties.

Rollover Phenomenon in Liquefied Natural Gas Storage Tank

Liquefied natural gas (LNG) rollover refers to the sudden mixing of stratified LNG layers, which can cause the generation of significant amounts of boil-off gas which create safety issues significantly in LNG storage tanks. Therefore, understanding of the phenomenon is very important for prevention purpose. Heat leak is a major challenge as it causes slow LNG boil-off leading to LNG stratification and LNG rollover phenomenon which has negative impact on people, environment, company asset and reputation. In this work, rollover phenomenon evolution is modeled and simulated using ANSYS FLUENT 16.0 software to study and analyze the effect of different ambient temperatures on the rollover phenomenon in LNG storage tanks and to study the stress distribution due to rollover and its effects on inner wall of the tank and determine the rollover time. This study examined the effect of different ambient temperatures ranged from 283 to 323 K on the LNG rollover inside a 5000 m3 LNG storage tank. Results show that higher temperature will cause higher heat transfer leaks to the LNG tank. The heat transfer through the tank walls is higher than the heat leaks to the tank through tank base. The pressure inside the LNG storage tank is strongly affected by the surrounding temperature. Higher temperature will cause higher pressure to build up in the tank especially along the area between the roof of the tank and the side walls. The simulations results show that significant initial density differences (∆ρ) between the stratified layers lead to late rollover events but last for longer time. At ∆ρ = 30, 15 and 7 kg/m3, the rollover will last for 3.1, 2.5 and 2.2 h, respectively.

Thermoeconomic optimization and comparison of the simple single-stage transcritical carbon dioxide vapor compression cycle with different subcooling methods for district heating and cooling

The transcritical carbon dioxide vapor compression cycle is commonly used for heating and cooling applications because of the high discharge temperature and large evaporation heat. Whereas, high return water temperature is usually required by the heating demands, which significantly degrades the system performances. Nowadays, various kinds of subcooling methods have been proposed for the transcritical carbon dioxide vapor compression cycle, but a systematic comparative study based on the trade-off between the thermodynamic efficiency and economic cost is needed to analyze the applicability of these methods for large-scale district heating and cooling applications. In this work, the hot water temperature increases from 323.15 K to 343.15 K for district heating, and chilled water temperature reduces from 285.15 K to 280.15 K for district cooling. The simple single-stage transcritical carbon dioxide vapor compression cycles using subcooling methods with and without expansion work recovery, including internal heat exchanger, dedicated mechanical subcooling, cooling tower and dry cooler, are respectively modeled from the energetic, exergetic and economic perspectives. Based on the dual-objective Jaya algorithm and Technique for Order of Preference by Similarity to Ideal Solution decision-making method, the parametric study is conducted with optimized system performances to analyze the effects of different ambient conditions, namely the winter mode with ambient temperature from 248.15 K to 278.15 K and the summer mode with ambient temperature from 288.15 K to 318.15 K, and the relative humidity from 30% to 90%. Afterwards, the optimal subcooling methods under different ambient temperatures are selected based on the overall optimization and comparative study. The effects of different ambient temperatures on the system performances vary with different subcooling methods without expansion work recovery, and the dry cooler is the optimal subcooling method at the ambient temperatures from 248.15 K to 268.15 K, while the cooling tower is suggested under ambient temperatures higher than 278.15 K in spite of the performance degradation with high relative humidity. Insignificant differences of system performances using different subcooling methods can be observed with expansion work recovery, and the internal heat exchanger is selected as the optimal subcooling method for winter-mode operations, while the cooling tower is also suggested as the suitable subcooling method in the summer mode.

Variable impact by ambient temperature on fatigue resistance of heat-treated nickel titanium instruments.

The purpose of this study was to evaluate the effect of different ambient temperatures on cyclic fatigue (CF) life of two NiTi rotary systems and correlate the results with martensitic transformation temperatures. Heat-treated NiTi Vortex Blue (VB) and EdgeSequel Sapphire (SP) instruments (tip sizes no. 20, 25, 30, 35, 40) were tested for CF resistance at room and body temperature (n = 20 each group) in a simulated canal (angle of curvature 60°; radius 3mm; center from instrument tip 4.5mm) with a motor controlled by an electric circuit. Mean half-life, beta and eta Weibull parameters were determined and compared. Two further instruments of each brand were subjected to differential scanning calorimetry (DSC). Temperature had an effect on fatigue behavior: all instruments lasted significantly longer at room than at body temperature. All VB significantly outlasted those of SP at body temperature; while smaller diameters of VB (size no. 20) were also significantly more resistant than SP when tested at room temperature; SP with larger diameters (sizes no. 30, no. 35, and no. 40) lasted significantly longer than VB did. Immersion in water at body temperature was associated with a marked decrease in the fatigue life of all rotary instruments tested. VB instruments were significantly more CF resistant at body temperature and showed the highest predictability in terms of fracture resistance. Rotary instruments manufactured with different post-machining heat treatment responded differently to changed ambient temperatures. DSC assessment of martensitic conversion temperatures helps to predict the behavior of nickel titanium rotaries in different environments.

Circadian rhythms of locomotor activity in captive Emin’s mole-rats,Heliophobius emini(Rodentia: Bathyergidae)

Many African mole-rats (Bathyergidae) exhibit distinct circadian rhythms, despite the fact that they are strictly subterranean and are very infrequently exposed to light. We investigated the circadian system of Emin’s mole-rats ( Heliophobius emini ) by exposing 13 individuals to different lighting regimes. The mole-rats were subjected to a standard 12-h light:12-h dark light cycle, followed by a constant darkness (DD) cycle to evaluate entrainment and endogenous rhythms of locomotor activity. After allowing the mole-rats to re-entrain to a 12L:12D light cycle, the light cycle was inverted to examine the duration of re-entrainment following a drastic change in the light cycle. Furthermore, we investigated the effect of different ambient temperatures on the locomotor activity of the mole-rats, and they were thus subjected to a 12D:12L light cycle at 20°C, 25°C, and 30°C. Lastly, mole-rats were presented with a long-day (16L:8D) and a short-day (8L: 16D) light cycle to look at the effect on preferred active time. The animals showed a preference for diurnal activity with 9 mole-rats entraining to the light cycle, and maintaining clear endogenous rhythms throughout DD. Subjects were excessively slow to re-entrain their activity to the inverted light cycle. When subjected to different ambient temperatures, individuals showed marked increases in average activity at 20°C, with the lowest average activity occurring at 30°C. The mole-rats maintained their diurnal preference regardless of day length, condensing their activity during the short-day light cycle, while extending their active period during the long-day cycle. These results suggest that Emin’s mole-rats are able to perceive light and entrain their locomotor activity to light cycles, albeit weakly. In addition, ambient temperature influenced the level of overall activity, indicating that these animals may use behavioral thermoregulation to maintain a constant body temperature.

Thermomechanical modeling and experimental investigation of transformation-induced creep and stress relaxation in shape memory alloy wires

Creep and relaxation phenomena are being observed in shape memory alloys, not only at high temperatures but also at room temperature, due to their martensitic transformation. Transformation-induced creep and stress relaxation in shape memory alloys occur due to temperature variations during loading and unloading cycles. In this work, a one-dimensional fully coupled thermomechanical model was employed to develop a continuum framework for studying these behaviors in shape memory alloy wires. A decrease or increase in stress was observed during forward or reverse transformation at a constant amount of strain, showing the stress relaxation and stress recovery, respectively. Similarly, the model predicts that strain increases or decreases when stress is held fixed in the course of forward or reverse transformation, meaning the phenomena of creep and creep recovery, respectively. This model provides the ability of investigating the effects of different ambient temperatures, strain rates, applied stresses and strains, and wire radii on the creep and relaxation responses of shape memory alloys. Relaxation and creep experiments at different ambient temperatures and loading or unloading rates were also done on NiTi wires, and the theoretical predictions were shown to be in a good agreement with the empirical observations.