Heat Dissipation Limit Research Articles

Investigation of spontaneous capillary flow and heat transfer characteristics in parallel microchannels based on phase-field model

• The mechanism of liquid surface oscillation in capillary flow is revealed. • Effect of channel structure on capillary flow and heat transfer is discussed. • A novel heat sink based on parallel capillary microchannels is constructed. • Non-circular heat sink obtains better capillary flow and heat transfer performance. Passive heat dissipation based on capillary flow has excellent applications in the thermal management of electronic devices and spacecraft due to its advantages of spontaneity and high stability. However, the conflicting relationship between capillary pressure and permeability in conventional sintered capillary wick severely limits its heat dissipation limit, and the complex and tortuous flow path is the key limiting factor. In this study, a novel close-packed capillary microchannel is constructed to provide an unobstructed flow path, and based on the phase-field model, the capillary flow and heat transfer characteristics of capillary microchannels with different structures are investigated. First, for the single channel, the oscillatory mechanism of phase interface in the initial stage of capillary flow, which has received little attention before, is revealed, which is mainly caused by the reconstruction of the advancing meniscus. This provides more nuanced insights into the initiating mechanism of capillary flow. In the noncircular channel, due to the change in curvature of the liquid surface at the acute angle and the expansion of the adsorption layer on the wall surface, the capillary velocity and heat transfer capacity improve compared to circular channels of equal hydraulic diameter. In addition, the effects of channel diameter and wettability on capillary flow and heat transfer are discussed. Capillary microchannels with better wettability and larger diameter achieve better capillary flow and heat transfer capabilities. On this basis, the parallel capillary microchannels inside the block are analyzed, and the non-circular channels achieve a higher capillary velocity while ensuring capillary pressure. Furthermore, the design of the noncircular section obtains a smaller thermal resistance and greater heat transfer efficiency, where the triangular microchannels show the best results. For the same hydraulic diameter and total block area, the performance decreases continuously as the inner angle of the channel increases. These results provide new ideas and a theoretical basis for designing high-performance passive heat sinks based on capillary flow.

Utilizing the Refrigerants R134a and Mixed Nano- Particle Refrigerant in a Comparison Study and Analysis of a Vapour Compression Refrigeration System

Abstract: Fundamentally, a vapour compression refrigeration system (VCRS) is a device that absorbs heat from a lower internal heat level and rejects it to the body or environment at a higher temperature in exchange for some external work being done on it. It is widely used everywhere, from commercial use in homes and stores to extensive scope and significant cooling loads in companies. They vary in size as well, but only to the extent necessary for cooling. to operate with top blowers, provide large cooling loads with minimal energy or force consumption Manyanalysts working in the subject of warm designing have always been interested in it. The area of refrigeration is similarly changing as a result of the introduction of nanotechnology in all research and technological fields. not anymore left clean of it. It has been observed that severalmetals and their combinations have high heat dissipation limits, which formed the basis for their use in refrigeration. Numerous nano size metal mixes have been tested with numerous refrigerants, and suitable fixes have been discovered to ensure an increased VCRS Coefficient of Execution. In this endeavour as well, a unique mixture is used, and research on VCRS will be conducted. Here, the task of finding the best fixations is completed afterthe mixing of metalCuO nanoparticles with the refrigerant R134a is complete.

Manipulation of Heat Dissipation Capacity Affects Avian Reproductive Performance and Output

Animal life requires hard work but the ability to endure such workload appears to be limited. Heat dissipation limit (HDL) hypothesis proposes that the capacity to dissipate the excess of body heat during hard work may limit sustained energy use. Experimental facilitations of heat loss rate via feather-clipping in free-living birds seem to support HDL hypothesis but testing of HDL through laboratory experiments under controlled conditions is not reported. We employed a two-factorial experimental design to test HDL hypothesis by manipulating the capacity to dissipate heat through exposure of captive zebra finches (Taeniopygia guttata) to a cold and warm ambient temperature (14°C and 25°C), and through manipulation of the insulating layer of feathers around the brood patch in females (clipped and unclipped). To simulate foraging costs encountered in the wild we induced foraging effort by employing a feeding system that necessitated hovering to access food, which increased energetic costs of reproduction despitead libitumconditions in captivity. We quantified the outcome of reproductive performance at the level of both parents, females, and offspring. Thermal limitations due to warm temperature appeared at the beginning of reproduction for both parents with lower egg-laying success, smaller clutch size and lower egg mass, compared to the cold. After hatching, females with an enhanced ability to dissipate heat through feather-clipping revealed higher body mass compared to unclipped females, and these clipped females also raised heavier and bigger nestlings. Higher levels for oxidative stress in plasma of females were detected prior to reproduction in warm conditions than in the cold. However, oxidative stress biomarkers of mothers were neither affected by temperature nor by feather-clipping during the reproductive activities. We document upregulation of antioxidant capacity during reproduction that seems to prevent increased levels of oxidative stress possibly due to the cost of female body condition and offspring growth. Our study on reproduction under laboratory-controlled conditions corroborates evidence in line with the HDL hypothesis. The link between temperature-constrained sustained performance and reproductive output in terms of quality and quantity is of particular interest in light of the current climate change, and illustrates the emerging risks to avian populations.

Reversible sweat cooling on mobile electronic devices by metal-organic frameworks-based moisture sorption-desorption process

The continuous improving performance of mobile electronic devices urges a larger heat dissipation capacity, while its improvement is encountering a bottleneck due to the limited cooling area and inherent property of natural convection and radiation. Fortunately, a novel passive cooling technique realized by the moisture sorption-desorption process offers new opportunities for enhancing heat dissipation. This article demonstrates the practical application of sorption-based reversible sweat cooling on a commercial 5G smartphone. In specific, about 1.7 g MIL-101(Cr) is coated on the back cover of the device. Comprehensive benchmarks are employed to evaluate the effectiveness of the moisture sorption-desorption process. Experimental results show that the proposed cooling strategy can bring an extra 0.59 W heat dissipation capacity (about 10% improvement), causing a maximum of 25% performance improvement in graphics-intensive gaming benchmarks. This sorption-based cooling strategy can break the heat dissipation limitation caused by heat radiation and natural convection, providing tremendous potential in the cooling of future electronics.

Heat Dissipation Characteristics of IGBT Module Based on Flow-Solid Coupling.

With the increase of power level and integration in electric vehicle controllers, the heat flux of the key silicon-based IGBT (Insulated Gate Bipolar Transistor) device has reached its physical limit. At present, third-generation semiconductor devices including SiC MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistor) are gradually replacing the dominant IGBT module. The hybrid IGBT module consists of both and can improve the performance and reduce the cost of controllers. Limits due to the installation space, location, and other conditions in the car make it difficult to meet the requirements of controllers with an air-cooled heatsink due to their large size and limited heat dissipation capacity. A smaller and more powerful water-cooled heatsink case is required to ensure the heat dissipation of the IGBT in the controller. Based on previous experience in finite element numerical simulation, hydrodynamics calculation, and heat transfer calculation, ANSYS Workbench finite element software was used to analyze the thermal resistance of each structure inside the module and the heatsink structure. The fluid characteristics and heat transfer performance of three different flow channel structures were analyzed, and the design of the cooling flow fin was improved to provide a reference for the heat dissipation of the hybrid IGBT module.

Keeping your cool: thermoregulatory performance and plasticity in desert cricetid rodents.

Small mammals in hot deserts often avoid heat via nocturnality and fossoriality, and are thought to have a limited capacity to dissipate heat using evaporative cooling. Research to date has focused on thermoregulatory responses to air temperatures (Ta) below body temperature (Tb). Consequently, the thermoregulatory performance of small mammals exposed to high Ta is poorly understood, particularly responses across geographic and seasonal scales. We quantified the seasonal thermoregulatory performance of four cricetid rodents (Neotoma albigula, Neotoma lepida, Peromyscus eremicus, Peromyscus crinitus) exposed to high Ta, at four sites in the Mojave Desert. We measured metabolism, evaporative water loss and Tb using flow-through respirometry. When exposed to Ta≥Tb, rodents showed steep increases in Tb, copious salivation and limited evaporative heat dissipation. Most individuals were only capable of maintaining Ta-Tb gradients of ∼1°, resulting in heat tolerance limits (HTLs) in the range Ta=43-45°C. All species exhibited a thermoneutral Tb of ∼35-36°C, and Tb increased to maximal levels of ∼43°C. Metabolic rates and rates of evaporative water loss increased steeply in all species as Ta approached Tb. We also observed significant increases in resting metabolism and evaporative water loss from summer to winter at Ta within and above the thermoneutral zone. In contrast, we found few differences in the thermoregulatory performance within species across sites. Our results suggest that cricetid rodents have a limited physiological capacity to cope with environmental temperatures that exceed Tb and that a rapidly warming environment may increasingly constrain their nocturnal activity.

Design and Evaluation of High-Speed FESS Converter for 1500 VDC Urban Rail Transit System

The urban rail transit system has the characteristics of wide voltage fluctuation, intermittent and strong impact load, limited heat dissipation capacity. The high-speed flywheel energy storage system (FESS) is used to provide network voltage stability and regenerative braking energy recovery due to its high power density, unlimited number of charge-discharge cycles, fast response and environmental friendliness. When considering the design of high-speed FESS converter with 3.6 kHz fundamental frequency and 330 kW rated power used in 1500 VDC urban rail transit system, the two-stage topological converter reduces the efficiency and increase the cost and size, meanwhile, the series-connected converters and the multilevel converter increase the difficulties of control and insulation, so the two-level and I-type three-level converters of high-speed FESS are designed and evaluated. Several comparisons are made by detailed experimental data from the perspective of the traction load characteristics of the 1500 VDC urban rail transit system and the technical and economical requirements of the high-speed FESS. It is found that the three-level converter has significant advantages in matching the traction load characteristics for its higher duty cycle capability, as well as improving the technical and economical performances such as efficiency, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">du/dt</i> value, THD, voltage stability, and reducing the cost by 40% when compared to the two-level converter. While in the future MW class high-speed FESS development, the maximum output power capacity of the three-level FESS is relatively lower than that of the two-level FESS. The theoretical analyses were verified by experiments.

The sputtering of titanium magnetron target with increased temperature in reactive atmosphere by gas injection magnetron sputtering technique

This paper presents a Gas Injection Magnetron Sputtering technique as a target temperature-controlling method. This technique is based on the generation of discrete plasmoids by injecting gas into the inter-electrode region. It provides control over the target temperature with limited heat dissipation by using various frequencies of plasma pulse generation. TiN and TiO2 coatings were selected as test materials for the study. Reactive sputtering processes with limited capability to cool the titanium target were carried out by generating a series of 500-ms plasma pulses at frequencies ranging from 0.5 to 1 Hz. The process variants allowed to achieve target temperatures ranging from 720 to 1210 °C. The results of structural, chemical and phase composition studies showed that the temperature of the target sputtering process did not influence the coatings' chemical and phase state. We have observed slight differences in the structure of TiO2 with the temperature since it is a material with a lower melting temperature than TiN. The differences in the thickness of fabricated coatings have been determined. In all the hot sputtering process cases, the deposited layers’ thickness was increased compared to the cold process. The growth kinetics normalized to the power effectivity decreases with the temperature due to the poisoning of the target material.

The role of flexural coupling in heat dissipation from a two-dimensional layered material to its hexagonal boron nitride substrate

Understanding the limits of phononic heat dissipation from a two-dimensional layered material (2DLM) to its hexagonal boron nitride (h-BN) substrate and how it varies with the structure of the 2DLM is important for the design and thermal management of h-BN-supported nanoelectronic devices. We formulate an elasticity-based theory to model the phonon-mediated heat dissipation between a 2DLM and its h-BN substrate. By treating the h-BN substrate as a semi-infinite stack of harmonically coupled thin plates, we obtain semi-analytical expressions for the thermal boundary conductance (TBC) and interfacial phonon transmission spectrum. We evaluate the temperature-dependent TBC of the N-layer 2DLM (graphene or MoS2) on different common substrates (h-BN vs. a-SiO2) at different values of N. The results suggest that h-BN is substantially more effective for heat dissipation from MoS2 than a-SiO2 especially at large N. To understand the limitations of the our stack model, we also compare its predictions in the limit to those of the more exact atomistic Green’s function model for the graphite–BN and molybdenite–BN interfaces. Our stack model provides clear insights into the key role of the flexural modes in the TBC and how the anisotropic elastic properties of h-BN affect heat dissipation.

A critical investigation into spontaneous combustion in coal storage bunkers

SYNOPSIS Spontaneous combustion (SC) is a cold oxidation reaction that generates heat, causing a temperature rise of the reactant and leading, with limited heat dissipation, to self-ignition of the reactant, which occurs without an external heat source. Although not limited to coal, the most significant hazard of SC are the fires that occur in coal mining operations around the world. These fires pose a serious risk to the safety of workers in the mines as well as adverse effects on the environment, and can affect the quality of life for current and future generations. We investigated the occurrence of SC in raw coal storage bunkers with the purpose of compiling a decision analyser for engineers designing or working with coal storage bunkers. Specific experts were interviewed from different backgrounds and companies, followed by field research at a coal mine. The important factors affecting the possibility of SC occurring were the type of coal supplied to the bunker, the mining practice, and physical conditions around the bunker. The information presented here will assist in reducing the SC risk in raw coal storage bunkers. These findings, together with the systematic decision analyser developed, will assist design engineers and mine personnel to take early preventative steps in managing SC. The decision analyser was tested for many different scenarios and gave good guidance on how to minimize and prevent SC in bunkers. Keywords: bunkers, coal storage, spontaneous combustion.

Suppression of self-heating in nanoscale interfaces using h-BN based anisotropic heat diffuser

Thermal management of integrated circuits (ICs) is becoming increasingly important as the feature-size of transistors is now comparable to the phonon mean free path, and the power density is reaching a critical level. The thermal effect is especially pronounced in 3D ICs with limited heat dissipation paths due to stacked transistors with insulators interposed between them. Hexagonal boron nitride (h-BN) is an insulating 2D material with a strong anisotropy in its heat-conducting property; the heat transfer coefficient is very high in the lateral direction, rivaling that of copper, but relatively low in the vertical direction. In this work, we studied the heat dissipation efficiency of integrated h-BN gate dielectrics with varying thicknesses in an environment similar to that of a stacked IC. High-power GaN transistors were interposed between thick insulators to emulate the hotspot propagation in a confined environment with minimized convective and radiative heat transfer. Devices were compared via in situ thermographic imaging, and at least a 20 K decrease in hotspot temperature was observed at the power density of 10 to 12.5 Wmm−1. Importantly, the drain current which was suppressed due to the self-heating effect was restored to its normal level after the heat conduction rate increased.

Forced convection in finned metal foams: The effects of porosity and effective thermal conductivity

Metal foams are promising candidates for enhancing the thermal performance of heat exchangers due to their unique features such as high surface-area-to-volume ratio and stochastic orientation. However, limited heat dissipation in high porosity metal foams is found to be a significant constraint on the heat transfer enhancement. To overcome this issue, metal foam structures with fins were proposed. On the other hand, the enhancement of heat transfer obtained by the addition of fins is connected to the porosity and effective thermal conductivity of metal foams. This relationship needs to be considered in the design of the structures with finned metal foams properly. This study, accordingly, investigates the effects of porosity and effective thermal conductivity on flow and heat transfer in a channel with finned metal foams. First, a numerical model was established and validated with the experimental data in the literature. Next, the flow and heat transfer characteristics of metal foams with different porosities and effective thermal conductivities were investigated under different fin configurations. The numerical results show that the addition of fins does not yield a considerable increase in the friction factor, and heat transfer shows a considerable increase up to the addition of a certain number of fins. When the fin number is further increased, the enhancement in heat transfer becomes relatively limited for all metal foams considered in this study. The effective fin number depends on the porosity and effective thermal conductivity. The results also show that the contribution of fins to the heat transfer in the parameter range considered in the study varies between 40-115% and 70–150% at the lowest and highest velocities, respectively.

The Ability to Dissipate Heat Is Likely to Be a More Important Limitation on Lactation in Striped Hamsters with Greater Reproductive Efforts under Warmer Conditions

The limitations on energy availability and outputs have been implied to have a profound effect on the evolution of many morphological and behavioral traits. It has been suggested that the reproductive performance of mammals is frequently constrained by intrinsic physiological factors, such as the capacity of the mammary glands to produce milk (the peripheral limitation [PL] hypothesis) or that of the body to dissipate heat (the heat dissipation limitation [HDL] hypothesis). Research on a variety of small mammals, however, has so far failed to provide unequivocal support for one hypothesis over the other. We tested the PL and HDL hypotheses in female striped hamsters (Cricetulus barabensis) with artificially manipulated litter sizes of two (three or four pups removed from natural litter size), five, eight (two or three pups added to natural litter size), and 12 (five to seven pups added to natural litter size) pups at ambient temperatures of 21° and 30°C. Energy intake and milk output of mothers, litter size, and litter mass were measured throughout lactation. Several markers indicating digestive enzyme activity and the gene expression of hypothalamic neuropeptides related to food intake were also measured. Food consumption and milk output increased with increasing litter size but reached a ceiling at 12 pups, causing 12-pup litters to have significantly lower litter mass and pup body mass than litters composed of fewer pups. Litter mass and maternal metabolic rate, milk output, maltase, sucrase, and aminopeptidase activity in the small intestine, and gene expression of hypothalamic orexigenic peptides were significantly lower at 30°C than at 21°C, and these differences were considerably more pronounced in 12-pup litters. These results suggest that PL and HDL can operate simultaneously but that the HDL hypothesis is probably more valid at warmer temperatures. Our results suggest that increased environmental temperatures in future climates may limit reproductive output through heat dissipation limits.

Thermal biology and growth of bison (Bison bison) along the Great Plains: examining four theories of endotherm body size

AbstractBody size of bison (Bison bison) declines with rising global temperature across the fossil record and rising annual temperatures across the Great Plains, but what are the underlying drivers? Body size depends on growth, which depends on maximizing net energy and nutrient flows for the production of tissues at seasonal scales across the range of the species. We measured thermoregulation costs of body surface temperature (°C) and heat exchanges (W and W/m2) of 350 adult and 345 adolescent Bison from 19 herds in summer and winter along the Great Plains from Saskatchewan (52° N) to Texas (30° N). At the smallest scale, daily body surface temperature increased with solar radiation and decreased with relative humidity and wind speed, which is consistent with Kooijman’s dynamic energy budget theory. Total surface heat transfer (W) increased with body mass (kg) at an exponent of 0.63 ± 0.03, which is consistent with Schmidt‐Nielsen’s principle of surface‐area‐to‐volume ratios (b = 0.67). On an annual scale, growth (kg/yr) of adolescent Bison decreased with increasing total surface heat transfer (W) during summer, which supports Speakman and Król’s heat dissipation limit theory. On the largest scale, heat flux was weakly related to latitude in summer and winter for adolescent Bison, which provides support for Bergmann’s rule and suggests a role for local primary production along the Great Plains. Cooler summers are more optimal for Bison growth because of reduced heat loads during the growing season. Rising temperatures are likely to constrain body size and productivity of Bison and other large endotherms in North America.

Waveform Control of Multi-Pulse Flat-Top High Magnetic Field Based on Pulsed Generator System

Multi-pulse flat-top high magnetic field (MFHMF) can promote neutron diffraction, terahertz source and other research fields. Due to the limited heat dissipation capability of pulsed magnet, the magnet resistance gradually increases, which leads to inconsistencies of the waveforms and limits the quantity of flat-top magnetic field waveforms. For the sake of getting the MFHMF with high consistency, a pulsed generator-rectifier system is used as the power supply by analyzing the impedance characteristic of multi-pulse magnet in this paper. Based on the accurate external characteristics modeling of power supply, a control method of generalized model predictive control (GPC) is proposed. In this GPC method, a 3-level least square method (LSM) is designed to calculate the real-time magnet resistance, and the influence of disturbance by the magnetic resistance is eliminated by the controller. Finally, the results based on MATLAB/ Simulink simulation verified the feasibility and validity of the waveform control method of MFHMF.

Limits to sustained energy intake. XXXII. Hot again: dorsal shaving increases energy intake and milk output in golden hamsters (Mesocricetus auratus).

Golden hamsters have four times the body size of mice, raise very large litters and are required to produce large quantities of milk during the 18-day lactation period. We have previously proposed that they may be prone to being limited by their heat dissipation capacity. Studies where lactating females are shaved to elevate their heat dissipation capacity have yielded conflicting data so far. With their short pregnancy of ∼18 days, the large litters and the reported high skin temperatures, they may serve as an ideal model to elucidate the role of epilation for energy budgets in lactating mammals. We shaved one group of lactating females dorsally on the sixth day of lactation, and tested if the elevated heat dissipation capacity would enable them to have higher energy intakes and better food-to-milk conversion rates. Indeed, we observed that females from the shaved group had 6% higher body mass and 0.78°C lower skin temperature than control females during lactation. When focusing on the phase of peak lactation, we observed significantly higher (10%) gross energy intake of food and 23.4% more milk energy output in the shaved females, resulting in 3.3 g higher individual pup weights. We conclude that shaving off the females' fur, even though restricted to the dorsal surface, had large consequences on female energy metabolism in lactation and improved milk production and pup growth in line with our previous work on heat dissipation limitation. Our new data from golden hamsters confirm heat dissipation as a limiting factor for sustained metabolic rate in lactation in some small mammals and emphasise the large effects of a relatively small manipulation such as fur removal on energy metabolism of lactating females.

Experimental facilitation of heat loss affects work rate and innate immune function in a breeding passerine bird.

The capacity to get rid of excess heat produced during hard work is a possible constraint on parental effort during reproduction [heat dissipation limit (HDL) theory]. We released hard-working blue tits (Cyanistes caeruleus) from this constraint by experimentally removing ventral plumage. We then assessed whether this changed their reproductive effort (feeding rate and nestling size) and levels of self-maintenance (change in body mass and innate immune function). Feather-clipped females reduced the number of feeding visits and increased levels of constitutive innate immunity compared with unclipped females but did not fledge smaller nestlings. Thus, they increased self-maintenance without compromising current reproductive output. In contrast, feather clipping did not affect the number of feeding visits or innate immune function in males, despite increased heat loss rate. Our results show that analyses of physiological parameters, such as constitutive innate immune function, can be important when trying to understand sources of variation in investment in self-maintenance versus reproductive effort and that risk of overheating can influence innate immune function during reproduction.

Limits to sustained energy intake. XXXI. Effect of graded levels of dietary fat on lactation performance in Swiss mice.

The heat dissipation limit theory predicts that lactating female mice consuming diets with lower specific dynamic action (SDA) should have enhanced lactation performance. Dietary fat has lower SDA than other macronutrients. Here we tested the effects of graded dietary fat levels on lactating Swiss mice. We fed females five diets varying in fat content from 8.3 to 66.6%. Offspring of mothers fed diets of 41.7% fat and above were heavier and fatter at weaning compared with those of 8.3 and 25% fat diets. Mice on dietary fat contents of 41.7% and above had greater metabolizable energy intake at peak lactation (8.3%: 229.4±39.6; 25%: 278.8±25.8; 41.7%: 359.6±51.5; 58.3%: 353.7±43.6; 66.6%: 346±44.7 kJ day-1), lower daily energy expenditure (8.3%: 128.5±16; 25%: 131.6±8.4; 41.7%: 124.4±10.8; 58.3%: 115.1±10.5; 66.6%: 111.2±11.5 kJ day-1) and thus delivered more milk energy to their offspring (8.3%: 100.8±27.3; 25%: 147.2±25.1; 41.7%: 225.1±49.6; 58.3%: 238.6±40.1; 66.6%: 234.8±41.1 kJ day-1). Milk fat content (%) was unrelated to dietary fat content, indicating that females on higher fat diets (>41.7%) produced more rather than richer milk. Mothers consuming diets with 41.7% fat or above enhanced their lactation performance compared with those on 25% or less, probably by diverting dietary fat directly into the milk, thereby avoiding the costs of lipogenesis. At dietary fat contents above 41.7% they were either unable to transfer more dietary fat to the milk, or they chose not to do so, potentially because of a lack of benefit to the offspring that were increasingly fatter as maternal dietary fat increased.

Heat dissipation capacity influences reproductive performance in an aerial insectivore.

Climatic warming is predicted to increase the frequency of extreme weather events, which may reduce an individual's capacity for sustained activity because of thermal limits. We tested whether the risk of overheating may limit parental provisioning of an aerial insectivorous bird in population decline. For many seasonally breeding birds, parents are thought to operate close to an energetic ceiling during the 2-3 week chick-rearing period. The factors determining the ceiling remain unknown, although it may be set by an individual's capacity to dissipate body heat (the heat dissipation limitation hypothesis). Over two breeding seasons we experimentally trimmed the ventral feathers of female tree swallows (Tachycineta bicolor) to provide a thermal window. We then monitored maternal and paternal provisioning rates, nestling growth rates and fledging success. We found the effect of our experimental treatment was context dependent. Females with an enhanced capacity to dissipate heat fed their nestlings at higher rates than controls when conditions were hot, but the reverse was true under cool conditions. Control females and their mates both reduced foraging under hot conditions. In contrast, male partners of trimmed females maintained a constant feeding rate across temperatures, suggesting attempts to match the feeding rate of their partners. On average, nestlings of trimmed females were heavier than controls, but did not have a higher probability of fledging. We suggest that removal of a thermal constraint allowed females to increase provisioning rates, but additionally provided nestlings with a thermal advantage via increased heat transfer during maternal brooding. Our data provide support for the heat dissipation limitation hypothesis and suggest that depending on temperature, heat dissipation capacity can influence reproductive success in aerial insectivores.

Augmented Cross-Entropy-Based Joint Temperature Optimization of Real-Time 3-D MPSoC Systems

3-D multiprocessor system-on-chip (MPSoC) systems can offer higher integration density, lower interaction cost, better bandwidth, and greater performance. However, vertically stacked silicon layers and limited heat dissipation paths result in high peak temperature and large temperature variation, which incur reliability reduction, lifetime decay, and performance degradation. In this article, we propose an offline augmented cross-entropy (CE)-based task scheduling strategy to jointly optimize peak temperature and temperature variation under the constraint of timeliness. Specifically, based on the conventional CE method, a heuristic iterative sampling method is designed to explore task-to-core assignment for balanced heat distribution between the top-layer and the bottom-layer cores. Subsequently, thermal characteristics of 3-D MPSoC systems are used to judiciously swap tasks between the two layers to improve the conventional CE-based task assignment and accelerate the iterative process. The peak temperature of individual cores is further reduced via sequencing, splitting, and slacking task execution. The experimental results demonstrate that compared to the existing state-of-the-art methods, the proposed scheme can reduce peak temperature by up to 8.02 °C and temperature variation by up to 24.78% without violating the timeliness of tasks.