Thermal Constraints Research Articles

Dendrocentric learning for synthetic intelligence.

Artificial intelligence now advances by performing twice as many floating-point multiplications every two months, but the semiconductor industry tiles twice as many multipliers on a chip every two years. Moreover, the returns from tiling these multipliers ever more densely now diminish because signals must travel relatively farther and farther. Although travel can be shortened by stacking tiled multipliers in a three-dimensional chip, such a solution acutely reduces the available surface area for dissipating heat. Here I propose to transcend this three-dimensional thermal constraint by moving away from learning with synapses to learning with dendrites. Synaptic inputs are not weighted precisely but rather ordered meticulously along a short stretch of dendrite, termed dendrocentric learning. With the help of a computational model of a dendrite and a conceptual model of a ferroelectric device that emulates it, I illustrate how dendrocentric learning artificial intelligence-or synthetic intelligence for short-could run not with megawatts in the cloud but rather with watts on a smartphone.

An actuator with tuneable resonant frequency for active vibration damping

This paper explores implementing active resonance frequency tuning of adaptive tuned vibration absorbers (ATVA) by coupling a vibration absorber comprising a voice coil actuator (VCA) and a sprung inertial mass to a solenoid actuator (SA). In this device, the DC current flowing through the SA generates negative magnetic stiffness and varies the equilibrium position of the nonlinear spring of the VCA, thus changing the effective stiffness of the system and its resonant frequency. The paper details the analytical design steps and the parametric sizing process of designing the SA to maximize its force density within defined magnetic, dimensions and thermal constraints. The design of the SA was verified using finite element analysis (FEA), manufactured and coupled to a VCA to make the complete ATVA system. The experimental results demonstrate the tunability of the resonance frequency of the ATVA by controlling the SA’s DC current. It is shown that the system’s resonance frequency can be shifted by up to 23% of the fundamental resonance frequency, which improves the effectiveness of the ATVA at damping a broader range of excitation frequencies.

Early snow melt and diverging thermal constraints control body size in arctic–alpine spiders

AbstractTo predict species’ responses to a rapidly changing environment, it is necessary to detect current clines of life-history traits and understand their drivers. We studied body size variation, a key trait in evolutionary biology, of two arctic–alpine lycosid spiders and underlying mechanisms controlling this variation. We used long time-series data of body size of spiders sampled in Norway, augmented with museum data. Individuals of both species sampled in areas and years with longer snow-free periods grew larger than individuals in areas and years with shorter snow-free periods. Interestingly, temperatures below 0 °C led to a larger body size in Pardosa palustris, while temperatures above 0 °C led to a larger body size in Pardosa hyperborea. We assume that P. palustris, as the generally larger species, is less sensitive to environmental variability and low temperatures, because it can retain more energy compared with a smaller species and, therefore, can invest more resources in its offspring. With rising temperatures, both species might profit from a higher resource availability. In a rapidly changing arctic–alpine environment, alterations in the life-history traits and adaptation strategies of spiders are expected, which, regarding body size, seem to be highly influenced by early snowmelt and diverging thermal constraints.

Are thermal constraints shaping foraging ant assemblages in tropical regions? Integrating thermal and morphological traits to understand consequences of land‐use transformation

Abstract Understanding mechanistic processes driving biodiversity change in land‐use transformation is paramount but challenging. Functional trait‐based approach provides a framework to understand the environmental filtering process of species composition shifts. Yet, trait selection bias may affect the results on forecasting species dynamics, subsequent analyses and the scope of conclusions, in particular, if most studies on terrestrial arthropods rely exclusively on the use of a subset of morphological traits. The integration of ecophysiological traits could then provide additional dimensions of environmental filtering caused by land‐use conversion. Our study investigates how land‐use conversion from forest to rubber plantation impacts functional traits distribution and trait space in foraging ant assemblages in tropical Thailand by integrating both physiological and morphological traits. The results showed that both physiological and morphological traits may explain, although unevenly, the differences observed in ant assemblages between forest and rubber plantation. The use of Critical Thermal maximum provided an important and unique role for differentiating assemblages encountered in both habitats and in characterising the niche structure of species assemblage from forest. The use of particular traits can thus improve our perception of species dynamic along land‐use gradient. To advance our knowledge on the species responses and consequences of land‐use changes, the use of different types of functional traits is recommended.

Electrothermal Multicriteria Comparative Analysis of Two Competitive Powertrains Applied to a Two Front Wheel Driven Electric Vehicle during Extreme Regenerative Braking Operations

The powertrain performance in an electric vehicle is fully dependent on the electrical and thermal constraints of the static converters ensuring the power transfer taking place between the energy storage systems and the electromechanical machines. These constraints depend on the architectures of the power converters, and their control strategies. Particularly, the maximal limits are reached in maneuvers such as hard regenerative braking circumstances. Indeed, braking recovery is a critical phase in the vehicle’s operation, and its duration and intensity may strongly impact the vehicle’s battery behavior or integrated hybrid storage system. The innovative objective of the paper is to propose an electrothermal multicriteria comparative study based on electrical and thermal criteria for two competitive powertrains. These semi-active power configurations (a 3-level DC/DC converter-based, and a Z-source converter-based) are implemented in a two-front wheel driven electric vehicle during extreme regenerative braking conditions. Open-loop and closed-loop controls were implemented in the Z-source using the maximal constant boost control with 3rd harmonic injection modulation technique. We considered two paralleled IGBT modules instead of the single shoot-through structure. Our approach is based on simulation during an extreme braking maneuver leading to heavy repercussions on the overall powertrain system. The aim is to investigate the challenging structure of the Z-source. Results showed that the proposed 3-level DC/DC-based topology has better performances in terms of power losses, efficiency, thermal behavior, and electromagnetic interference.

A general framework for jointly modelling thermal and hydric constraints on developing eggs

Abstract Eggs are a vulnerable stage because they are sensitive to thermal and hydric conditions and yet cannot behaviourally avoid stressful environments. A general mechanistic model of egg development in natural nests requires microclimatic predictions of temperature, humidity, radiation (if above ground) and water potential (if buried in soil) to be integrated with models of heat and water exchange of the egg and the metabolism of the developmental process. Although all the required pieces for such a model now exist, they have not been integrated into a general modelling framework. We developed such an integration using NicheMapR package for mechanistic niche modelling. Specifically, we took an existing general model of egg water exchange and connected it with the microclimate model in NicheMapR to simulate nest thermal and hydric environments, including the effects of soil water potential on liquid and vapour exchange and moisture‐mediated soil thermal conductivity on heat exchange. We then used the Dynamic Energy Budget model within the ectotherm model of NicheMapR as the mechanistic engine for the developmental process, allowing the explicit computation of the dynamics of metabolic heat production and all aspects of mass exchange. We illustrate the modelling framework using existing laboratory and field data on reptiles, insects, and birds. We show that it can capture laboratory observations of water exchange and metabolic heat production and how it can be used to map potential development and water uptake under natural conditions at the continental scale. The modelling framework can be used to interpret laboratory experiments and allows strong inferences to be made about the abiotic constraints on egg development in natural nests under past, present, and future environmental change.

Temperature shifts associated with bat arousals during hibernation inhibit the growth of Pseudogymnoascus destructans.

Temperature is a critically important factor in many infectious disease systems, because it can regulate responses in both the host and the pathogen. White-nose syndrome (WNS) in bats is a severe infectious disease caused by the temperature-sensitive fungus, Pseudogymnoascus destructans (Pd). One feature of WNS is an increase in the frequency of arousal bouts (i.e. when bat body temperatures are elevated) in Pd-infected bats during hibernation. While several studies have proposed that increased frequency of arousals may play a role in the pathophysiology of WNS, it is unknown if the temperature fluctuations might mediate Pd growth. We hypothesized that exposure to a high frequency of elevated temperatures would reduce Pd growth due to thermal constraints on the pathogen. We simulated the thermal conditions for arousal bouts of uninfected and infected bats during hibernation (fluctuating from 8 to 25°C at two different rates) and quantified Pd growth in vitro. We found that increased exposure to high temperatures significantly reduced Pd growth. Because temperature is one of the most critical abiotic factors mediating host-pathogen interactions, resolving how Pd responds to fluctuating temperatures will provide insights for understanding WNS in bats and other fungal diseases.

Nonlinear Thermal Diffusion and Radiative Stagnation Point Flow of Nanofluid with Viscous Dissipation and Slip Constrains: Keller Box Framework Applications to Micromachines

The radiated flow of magnetized viscous fluid subject to the viscous dissipation phenomenon is numerically studied. The radiative phenomenon is addressed with nonlinear relations. Further, analysis is performed by using the slip effects and convective thermal flow constraints. The transformed problem is numerically evaluated using the Keller Box method. The physical parameter effects, such as the magnetic parameter for the velocity profile, Prandtl number, Brownian motion parameter and Biot number for the energy profile and Lewis number, and the thermophoresis parameter for the concentration profile are discussed. The obtained results suggest applications in enhancing the heat transfer phenomenon, thermal system, energy generation, heat transmission devices, power generation, chemical reactions, etc.

Physical Interpretation of Nanofluid (Copper Oxide and Silver) with Slip and Mixed Convection Effects: Applications of Fractional Derivatives

A fractional model was developed for presenting the thermal assessment of nanoparticles in an inclined moving surface. Water was used as a base fluid, while the nanofluid utilized copper oxide and silver nanoparticles. The modification of the thermal model was further supported by mixed convection, magnetic force, and porous saturated space. Slip effects to the porous surface were also introduced. The fluctuation in temperature at different times was assumed by following the ramped thermal constraints. The fractional computations for the set of flow problems were performed with implementations of the Atangana–Baleanu (AB) and Caputo–Fabrizio (CF) analytical techniques. The integration process for such computations was achieved using the Laplace transformation. The comparative velocity and thermal analysis for the water and kerosene-oil-based nanofluid model is presented. The declining change in the velocity was observed due to the increase in the volume fraction of nanoparticles. It was observed that the increment in the temperature profile was more progressive for the kerosene oil and silver nanoparticle suspension.

A Multi-objective optimization for batch chemical reaction Processes: The trade-off between economy and safety

he thermal safety is always a challenging topic in the case of batch reactors carrying exothermic reactions. To reduce the risk of thermal runaway from both perspectives of likelihood and severity, it is desirable and practicable to develop a multi-objective optimization framework which can achieve trade-off between economy and safety. Therefore, this work provided an optimization framework for batch chemical reactor design with inherent safer operating and equipment parameters through maximizing yield of the target product while minimizing degree of Dow’s fire and explosion index along with thermal runaway constraints. Thermal runaway criteria, including temperature limit and divergence criterion, are employed as safety constraints. The response time is calculated with the optimal schemes selected from the Pareto solutions by a multi-attribute decision-making method (MADM). Finally, two examples for specific reaction systems with given kinetics are performed to demonstrate the feasibility and validity of the proposed method.

On prescribed thermal distributions of bioconvection Williamson nanofluid transportion due to an extending sheet with non-Fourier flux and radiation

Bio-convection, Cattaneo-Christov, and thermal radiation fluxes are accompanied by mixed convection flow of Williamson nano-fluids. The dynamics of the fluid occur due to an extendable surface with two thermal boundary constraints; the prescribed heat flux and surface temperature. The objective of this exploration pertains to effective and efficient thermal distributions. Theoretical layout is formulated in the form of a partial differential format. In order to attain the numerical resolution of this non-linear formulation, similarity transforms are employed to modify them into ordinary differential forms. The computational code for the Runga-Kutta procedure is developed in a MATLAB script. The temperature of fluids enhances with mounting strength of prescribed heat flux, thermophoresis, thermal radiation, magnetic field, Brownian motion and heat source but it descends against thermal relaxation time. The speed of fluids undergoes retardation against exceeding inputs of Williamson parameter λ, parameters of porosity, and magnetic body force. The range of distinct parameters while computing graphically is taken as , , , , , , , , , , , , , , and .

(Invited) Advancing 3D Packaging for Heterogenous Systems Integration

Next generation computing architectures including those for machine learning and AI (Artificial Intelligence) have increasing demands on bandwidth, memory capacity and energy efficiency. All of which can be improved through the increased integration density offered by advanced packaging technologies. In this talk, we will provide an overview of the different 3D integration technologies and cover their scaling and application considerations. These include technologies for direct die to die connections such as advanced solder interconnects at 20 and 10 µm pitch and hybrid bonding or Foveros Direct to support increased interconnect density to below 10 µm pitch or more than 10,000 connections/mm2. The increased interconnect density can dramatically improve the bandwidth capability and energy efficiency. We will also cover some of the considerations for 3D die stacking such as thermal hot spots and power delivery constraints and how these can be addressed through design and packaging technology combinations. Finally, we will discuss some future directions to support continued performance improvement.

Role of crustal fluids and thermo-mechanical structure for lower crustal seismicity: The Gargano Promontory (southern Italy)

Several regions around the globe are characterized by a seismically active lower crust, at depths where lithological and thermal conditions suggest stress release by ductile flow. The Gargano Promontory (GP, southern Italy) is an example where a recently installed seismic network has recorded an intense seismic activity at depths between 20 and 30 km, i.e. in the lower crust. The GP is located in proximity of the Gargano-Dubrovnik lineament, a seismogenic zone separating the central and southern Adriatic basins. These two basins constitute sites of sediments accumulation since Tertiary times. Another important basin in the region is represented by the Apennine foredeep, that includes the Candelaro area. We analyze the possible mechanisms controlling the distribution of seismicity in the GP to identify the factors that make the lower crust seismically active. To this aim, we construct a thermo-rheological model of a layered continental crust, calibrated on the basis of geometrical, lithological and thermal constraints. The model takes into account various crustal lithologies, the presence of fluids in the crystalline basement, lateral variations of geotherm and stress field. The numerical simulations show that the presence of fluids is a key factor controlling the cluster of seismicity in the lower crust. Moreover, the presence of water in the upper crystalline basement and sedimentary cover provides a plausible explanation for upper crustal seismicity in a zone of very high heat flow SW of the GP. The distribution of the seismicity is probably affected by the composition of the crystalline basement, with mafic bodies injected into the crust during the Paleocene magmatic phase that affected the Mediterranean region. In addition, fluid accumulation and overpressure may occur along detachment levels in the lower crust, leading to clustering of the earthquakes. Based on our findings, we hypothesize that the presence of hydrous diapiric upwelling(s) in the upper mantle can feed a deep fluid circulation system, inducing lower crustal seismicity. • A thermo-rheological model to explain lower crustal seismicity in the Gargano Promontory (Italy) is presented. • Fluid presence controls the Gargano seismic activity in the lower crust. • The Gargano crust is injected by mafic bodies at various depths.

Thermal-Aware Design for Approximate DNN Accelerators

Recent breakthroughs in Neural Networks (NNs) have made DNN accelerators ubiquitous and led to an ever-increasing quest on adopting them from Cloud to edge computing. However, state-of-the-art DNN accelerators pack immense computational power in a relatively confined area, inducing significant on-chip power densities that lead to intolerable thermal bottlenecks. Existing state of the art focuses on using approximate multipliers only to trade-off efficiency with inference accuracy. In this work, we present a thermal-aware approximate DNN accelerator design in which we additionally trade-off approximation with temperature effects towards designing DNN accelerators that satisfy tight temperature constraints. Using commercial multi-physics tool flows for heat simulations, we demonstrate how our thermal-aware approximate design reduces the temperature from 139 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C, in an accurate circuit, down to 79 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C. This enables DNN accelerators to fulfill tight thermal constraints, while still maximizing the performance and reducing the energy by around 75% with a negligible accuracy loss of merely 0.44% on average for a wide range of NN models. Furthermore, using physics-based transistor aging models, we demonstrate how reductions in voltage and temperature obtained by our approximate design considerably improve the circuit’s reliability. Our approximate design exhibits around 40% less aging-induced degradation compared to the baseline design.

Plant diversity and functional identity alter ant occurrence and activity in experimental grasslands

AbstractIncreasing plant species richness has been shown to positively affect the diversity of a range of other organisms, both above‐ and belowground. Although ants have a multitude of interactions with other organisms through their role as predators and mutualists, ants are a taxon that has rarely been investigated in studies of biodiversity effects. Ants are known to respond to changes in microclimatic conditions such as temperature and humidity, and these microclimatic conditions are known to be affected by vegetation characteristics such as standing biomass, which in turn can be affected by plant diversity. We investigated the effects of plant species richness (1–60), the number of plant functional groups (FGs; 1–4), and the presence of particular FGs on the occurrence and activity of ants, in the context of a grassland biodiversity experiment. Ant abundance, estimated as the mean number of workers in pitfall traps, and the number of colonies within plots, but not ant species richness, were negatively affected by plant species richness, and also by the identity of plant FGs, particularly legumes (negative effects) and grasses (positive effects). Statistical approaches showed that these effects were largely mediated by biotic (aboveground plant biomass: negative effect) and abiotic variables (soil temperature: positive effect). Notably, ant activity, measured as the mean number of workers foraging on baits and with a disproportionate dominance of a single species (Lasius niger), showed a more complex pattern, where plant species richness and number of FGs interacted to explain differential attractiveness to different resources (represented by sugar and tuna baits), likely representing current nutritional requirements for ants. Similarly, increasing soil temperature increased the level of ant activity, indicating that abiotic factors might impose thermal constraints on ectotherms inhabiting temperate grasslands. Our results indicate that a higher number of plant species and higher plant biomass had a negative effect on ants in experimental grasslands. Understanding the responses of an ecologically important group such as ants will allow us to infer the effects that biodiversity loss could have on animal‐mediated ecosystem processes.

Advances in In-situ Boron and Phosphorous Doping of SiGeSn

Dopant concentrations higher than 1x1019 cm-3 are required to improve the performances of various GeSn based devices such as photodetectors, electrically pumped lasers and so on. In this study, the in-situ Boron and Phosphorous doping of SiGeSn was investigated, building upon recent studies on in-situ B or P doped GeSn. The surfaces of intrinsic and lowly doped pseudomorphic SiGeSn layers were rough. By contrast, a <110> cross hatch was recovered and surfaces as smooth as the Ge Strain-Relaxed Buffers underneath were obtained for the highest B2H6 or PH3 mass-flows. The surface Root Mean Square roughness and Zrange values were then as low as 0.36 nm and 2.86 nm for SiGeSn:B, and 0.47 nm and 4.60 nm for SiGeSn:P. In addition, Si contents as high as 25% were obtained, notably in SiGeSn:B layers. Dopants were almost fully electrically active in those SiGeSn:B and SiGeSn:P layers, with carrier concentrations as high as 2.0x1020 cm-3 and 2.7x1020 cm-3, respectively. For SiGeSn:P, the shortcoming of in-situ doped GeSn:P was overcome, that is the formation of electrically inactive SnmPnV clusters for high PH3 mass-flows. Such electrically active carrier concentrations will be beneficial for (Si)GeSn based devices, but also for all Group-IV based devices with extremely low thermal budget constraints.

Environmental temperature predicts resting metabolic rates in tropidurinae lizards.

Interspecific variation in metabolic rates may be associated with climate, habitat structure, and resource availability. Despite a strong link between ecology and physiology, there is a dearth in the understanding of how the costs of body maintenance change during ecological transitions. We focused on an ecologically diverse group of neotropical lizards (Tropidurinae) to investigate whether and how resting metabolic rate (RMR) evolved under divergent micro- and macrohabitat conditions. Using a phylogenetic framework, we tested whether species from hot and dry habitats had lower RMRs in relation to those from cooler and mesic habitats, and investigated whether microhabitat usage had an effect over body mass-adjusted RMRs. Our results suggest that RMRs are not phylogenetically structured in Tropidurinae. We found no correlation between metabolism, precipitation, and microhabitat usage. Species from warmer habitats had lower RMR compared to those from cooler habitats, supporting a mechanism of negative compensation in metabolic responses to temperature. Ectotherms from warmer habitats can limit energetic demand and expenditure through reduced RMR, whereas those from cooler habitats may sustain activity despite thermal constraints via increased RMR. Our work highlights the role of temperature in shaping metabolic responses in lizards, giving additional support to the notion that physiology and ecological contexts are intertwined.

Core optimization of UO2 fuelled ALLEGRO reactor

Feasibility of UO2 core is investigated considering neutronic and thermal constraints. Calculations showed that the amount of UO2 fuel must be increased significantly to reach criticality. Irradiation time needed to reach the target value of 75dpa increases by increasing fuel amount and keeping total thermal power constant. Changes in fuel composition and design-related differences of fissile isotope vectors in depleted fuel were studied. Beta effective value, void, Doppler and fuel expansion coefficients were calculated. Compliance to the shutdown criteria is demonstrated since reactivity worth of control rods is affected by the modifications of the core design. Assembly and pin-wise power distribution, as well as axial power distribution is examined for different core designs. Reactivity changes were calculated for the case of water ingress to the core as a result of design a basis event PRISE.

A Multilevel Control Approach to Exploit Local Flexibility in Districts Evaluated under Real Conditions

The increasing penetration of renewable energy sources creates a challenge for the stability of current power systems due to their intermittent and stochastic nature. This paper presents the field results of an efficient demand response solution for controlling and adjusting the electric demand of buildings in an energy district through the activation of their thermal mass while respecting the occupants’ thermal comfort constraints. This multilevel control approach aims to support grid flexibility during peak times by constraining the energy exchange with the grid and increasing the self-consumption of the district. The results show a great potential for increasing the self-consumption up to 37% for offices, as well as improving the indoor environment, based on real data collected from a case study in Greece.

Computational study of micro-polar nanofluid past a spinning disk with non-Fourier's heat and non-Fick's mass flux models

In this study, the flow of micro-polar nanofluid past a spinning disk with non-Fourier's heat and non-Fick's mass flux models has been scrutinized. The flow is considered under the effect of the concentration slip, velocity slip, convective heating, and radial magnetic field. Through boundary layer approximations, the acquired system of partial differential equations from conservations of mass, momentum, energy, and nanoparticles concentration was converted into ordinary differential equations using similarity transformation, and thereafter solved numerically by the bvp4c approach. Plots and tables are used to inspect and analyze the role of physical parameters on flow fields. It is evident from the results that the centrifugal, tangential, and angular velocities significantly deteriorate with an escalation of magnetic field constraints. Also, a declination in the motion of fluid flow along with the centrifugal and tangential surfaces happens with higher micro-rotation constraints. It is discovered from the results that the strengthening in angular velocity is caused by a higher micro-rotation slip parameter. Furthermore, heat relocation can be improved by higher magnetic field constraints, Brownian motion constraints, and thermal Biot number. However, it can be illustrated from the results that an enhancement in thermal relaxation constraint causes a reduction in temperature dissemination. The results also showed that an increment in concentration relaxation and concentration slip parameters causes a reduction in dissemination of concentration. The analysis of skin friction, wall couple stress, heat relocation rate, and mass relocation rate are premeditated via tables. This theoretical and numerical exploration is more helpful in industrial areas and in the field of biological research.