Thermal Constraints Research Articles

Shape and size of large-scale vortices: A generic fluid pattern in geophysical fluid dynamics

Planetary rotation organizes fluid motions into coherent, long-lived swirls, known as large-scale vortices (LSVs), which play an important role in the dynamics and long-term evolution of geophysical and astrophysical fluids. Here, using direct numerical simulations, we show that LSVs in rapidly rotating mixed convective and stably stratified fluids, which approximates the two-layer, turbulent-stratified dynamics of many geophysical and astrophysical fluids, have a generic shape and that their size can be predicted. We show that LSVs emerge in the convection zone from upscale energy transfers and can penetrate into the stratified layer. At the convective-stratified interface, the LSV cores have a positive buoyancy anomaly. Due to the thermal wind constraint, this buoyancy anomaly leads to winds in the stratified layer that decay over a characteristic vertical length scale. Thus LSVs take the shape of a depth-invariant cylinder with a finite-size radius in the turbulent layer and of a penetrating half dome in the stratified layer. Importantly, we demonstrate that when LSVs penetrate all the way through the stratified layer and reach a boundary that is no-slip, they saturate by boundary friction. We provide a prediction for the penetration depth and maximum radius of LSVs as a function of the LSV vorticity, the stratified layer depth, and the stratification. Our results, which apply for cyclonic LSVs, suggest that LSVs in slowly rotating stars and Earth's liquid core are confined to the convective layer, while in Earth's atmosphere and oceans they can penetrate far into the stratified layer.

Level set topology optimization of structures under stress and temperature constraints

In this paper, we introduce a level set topology optimization formulation considering coupled mechanical and thermal loads. Examples considering stress and compliance minimization under temperature and volume constraints, and mass minimization under stress and temperature constraints, are presented. The p-norm of the stress field and temperature field is used to approximate the maximum stress and temperature, respectively. We show that the minimal compliant topologies under temperature constraints do not necessarily have low stress values, and the stress and temperature requirements can be conflicting. The results also show that designs obtained by ignoring the thermal or structural constraints can result in high values of temperature or stress, respectively, thus demonstrating the importance of using a coupled multi-physics model in the optimization.

CMOS Compatible Atomic-Precision Donor Devices

Atomic precision advanced manufacturing (APAM) is a technique for placing dopant atoms with single atomic-lattice site precision on silicon surfaces. APAM devices are created by patterning the placement of dopants into a two-dimensional sheet of phosphorus atoms on the silicon surface, incorporating the dopants into the lattice, and then capping the device in silicon. The dopant atoms are incorporated into the silicon lattice through a surface-activated chemical reaction, as opposed to a thermally activated bulk process, which allows for electrically active doping above the solubility limit for phosphorus in silicon. The two-order of magnitude higher doping levels and two-dimensional nature of the dopant sheet enable new device physics and the potential for new device types with superior performance under specific tasks.Atomic precision fabrication requires atomically clean surfaces. Historically the APAM technique has required temperatures in excess of 1200 °C to prepare device surfaces, which has severely limited the ability to combine APAM with other manufacturing techniques such as CMOS. Recent work by our group and others has shown that the surface preparation process can be achieved at temperatures near 800 °C, greatly improving integration possibilities with CMOS [1,2]. Once fabricated, APAM devices have low thermal budgets to minimize vertical diffusion of the phosphorus dopants out of the non-equilibrium two-dimensional sheet. Temperatures on the order of 450 °C have been shown to be permissible for long periods of time.In this talk we report on the initial development of a CMOS process flow that incorporates APAM device fabrication. Based on the thermal budget and processing constraints, our basic process flow involves building the APAM device between CMOS Front-end-of-line (FEOL) and the CMOS Back-end-of-line (BEOL) steps. This is a natural insertion point based upon both thermal budget limitations and the need to directly access the device silicon to build the APAM device. Borrowing from CMOS nomenclature, we introduce the concept of “APAM select” and “APAM active” to indicate where the window for APAM device patterning will be opened and the actual APAM device area, respectively. These are the only additional mask layers needed to introduce APAM into a CMOS layout cell. An APAM cell was created that has the appropriate source/drain placement and targeting reticle in poly-Si to enable alignment of the APAM lithography tool to the wafer.Two classes of challenges exist in developing a CMOS-APAM process flow. The first is related to the APAM process itself and limitations of current fabrication tools. The APAM surface preparation, patterning, dopant incorporation, and silicon capping all occur in a scanning tunneling microscope (STM). Devices must be processed at the die level to fit into the STM sample holders. Die level processing puts restrictions on the BEOL processing including minimum feature size and available processes, such as a lack of chemical-mechanical polish (CMP) to planarize metal layers. The second class of challenges is related to the impacts of the APAM process, such as surface preparation, on CMOS devices, which has not been previously explored. We discuss our strategy for integration with CMOS, by including test structures to mimic the APAM device, and sequential implementation and testing of the APAM fabrication steps with CMOS chips.We conclude with a discussion of future integration challenges such as wafer level processing of APAM devices in a CMOS foundry flow. Direct integration of APAM components into CMOS circuits opens the door for devices with enhanced functionality.ACKNOWLEDGMENTThis work is supported by Sandia’s Lab Directed Research and Development Program, and was performed in part at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Structural shear performance of insulated precast concrete sandwich panels with steel plate connectors

Precast concrete sandwich panels are an increasingly popular means of building cladding. They can be designed with high thermal resistance by embedding abundant insulation between two concrete wythes. Steel, in the form of thin plate connectors, remains one of the most common tie materials to support the outer wythe of concrete vertically, and transmit lateral forces from the external rain-screen to the internal structural wythe. The optimum design of steel shear connectors must satisfy thermal and strength capacity constraints. An extensive experimental study analyses the structural shear performance of precast concrete sandwich panels with steel plate connectors of various dimensions that give rise to different load capacities, stiffnesses and failure modes.

Beaver (Castor fiber) activity and spatial movement in response to light and weather conditions

Animal behaviour can affect individual fitness and is influenced by exogenous and endogenous factors. Here, we investigated how light (daylight length and moonlight), weather (precipitation and temperature), age, sex and social status affected activity and movement of a semiaquatic mammal, the Eurasian beaver (Castor fiber), using GPS relocation data from 47 individuals in south-eastern Norway. Independent of daylight length, beavers had a mean daily activity time of 9:42 h and reduced their activity periods when they were older, most likely due to senescence. In line with this, older individuals also spent less time in water and moved shorter distances. Furthermore, beavers reduced their activity periods in drier weather conditions and spent less time on land during brighter nights and drier conditions, indicating a predation risk avoidance strategy. Individuals spent less time in the water during the colder parts of the year and moved shorter distances with decreasing temperature, suggesting thermal constraints. Our study adds to the increasing amount of evidence that animal behaviour is modulated by various endogenous and exogenous factors, and that weather conditions can affect their behaviour. It remains to be tested, however, how climate variability together with hunting and predation pressure affect space use and demography in species such as the Eurasian beaver.

Pigeons in the sun: Thermal constraints of eumelanic plumage in the rock pigeon (Columba livia).

In wild vertebrates, several species exhibit eumelanic color polymorphism with the coexistence of dark and light morphs. The maintenance of such polymorphism suggests the existence of a selective balance between the morphs and a large body of literature has reported the costs and benefits of darker plumage coloration in birds. Among them, it has been suggested that melanin and dark plumage could entail high energetic costs especially under hot and sunny climates. However, to my knowledge, the thermal constraints of sun exposure have rarely been studied in polymorphic species. Here, we tested the impact of eumelanic plumage coloration on plumage and body temperatures, and evaporative cooling behavior in the polymorphic rock pigeon (Columbia livia). We experimentally exposed light and dark pigeons to direct sun radiation for 1h while a few birds were maintained in the shade as controls. We found that sun exposure was associated with increased plumage temperature, and this effect was greater for darker pigeons. In addition, we found that sun exposure was also associated with higher cloacal temperature but for dark pigeons only. Finally, light and dark pigeons were more likely to show cooling evaporative behavior when exposed to sun and as their cloacal temperature increases. Altogether, these results suggest that darker pigeons may have a lower ability to cope with heat and solar radiations and that dark plumage can be associated with thermal costs in this polymorphic species.

Optimal peak flux density model (OPFDM) for non‐iterative design of high‐frequency gapped transformer (HFGT) in LLC resonant converters

In LLC resonant converters, litz-wire high-frequency gapped transformer (HFGT) is one of the most critical components, responsible for efficient operation. However, it is also a major contributor to overall weight and volume. Therefore, designers perform multi-objective optimisation for minimising its losses and size, which is itself complex and cumbersome. This usually requires many iterations because the losses vary non-linearly with the decrease in size. The selection of initial-setup parameter (ISP) values, plays a vital role in overall performance improvement of the optimisation. The closer the ISPs to optimal values, the smaller are the iterations required for convergence. Therefore, this study proposes an optimal peak flux density model (OPFDM), considering the voltage excitation waveform, duty cycle, core material parameters, and the response of litz-wire to high-frequency. The aim is to obtain an optimised HFGT design through a non-iterative approach by directly estimating optimal values of ISPs through OPFDM. The designed HFGT results in minimised losses and size, while keeping the thermal constraints within limits. Moreover, the impact of frequency and duty cycle on OPFDM is also presented. The proposed model is implemented to design HFGT for 380 VDC/12 VDC LLC converter. Comparison-based analytical, finite-elements method and experimental results validate the model.

Efficacy of Topology Scaling for Temperature and Latency Constrained Embedded ConvNets

Embedded Convolutional Neural Networks (ConvNets) are driving the evolution of ubiquitous systems that can sense and understand the environment autonomously. Due to their high complexity, aggressive compression is needed to meet the specifications of portable end-nodes. A variety of algorithmic optimizations are available today, from custom quantization and filter pruning to modular topology scaling, which enable fine-tuning of the hyperparameters and the right balance between quality, performance and resource usage. Nonetheless, the implementation of systems capable of sustaining continuous inference over a long period is still a primary source of concern since the limited thermal design power of general-purpose embedded CPUs prevents execution at maximum speed. Neglecting this aspect may result in substantial mismatches and the violation of the design constraints. The objective of this work was to assess topology scaling as a design knob to control the performance and the thermal stability of inference engines for image classification. To this aim, we built a characterization framework to inspect both the functional (accuracy) and non-functional (latency and temperature) metrics of two ConvNet models, MobileNet and MnasNet, ported onto a commercial low-power CPU, the ARM Cortex-A15. Our investigation reveals that different latency constraints can be met even under continuous inference, yet with a severe accuracy penalty forced by thermal constraints. Moreover, we empirically demonstrate that thermal behavior does not benefit from topology scaling as the on-chip temperature still reaches critical values affecting reliability and user satisfaction.

Palaeoproterozoic Mafic magmatism in the Indian Shield: Petrologic, Geochemical and Thermal constraints on Proterozoic Mantle

Palaeoproterozoic Mafic magmatism in the Indian Shield: Petrologic, Geochemical and Thermal constraints on Proterozoic Mantle

Simultaneous Management of Peak-Power and Reliability in Heterogeneous Multicore Embedded Systems

Analysis of reliability, power, and performance at hardware and software levels due to heterogeneity is a crucial requirement for heterogeneous multicore embedded systems. Escalating power densities have led to thermal issues for heterogeneous multicore embedded systems. This paper proposes a peak-power-aware reliability management scheme to meet power constraints through distributing power density on the whole chip such that reliability targets are satisfied. In this paper, we consider peak power consumption as a system-level power constraint to prevent system failure. To balance the power consumption, we also employ a Dynamic Frequency Scaling (DFS) method to further reduce peak power consumption and satisfy thermal constraints on the chip. We illustrate the benefits of our scheme by comparing it with state-of-the-art schemes, resulting in average in 26.5 percent less peak power consumption (up to 54.3 percent).

Standardized Heat Spreader Design for Passive Cooling of Interconnects in the BEOL of ICs

The back-end components of integrated circuits (ICs) are susceptible to self-heating deteriorating effects due to the microscale interconnects carrying large current densities, and thus require innovative passive cooling strategies. This article investigates the cooling effect of the high conductivity metallization (MET) fill that is used in conjunction with the chemical mechanical planarization (CMP) process. Thermal simulation models are developed for a three-level back end of line (BEOL) stack and then validated experimentally using high-resolution thermal imaging. A coupled approach is used to optimize the numerical model and fully characterize the BEOL embedded passive cooling solution. Results indicate that stricter thermal constraints are present for devices higher in the BEOL stack and exhibit the highest cooling potential from the use of CMP fill in the underlying MET layers. As a thermal improvement strategy for such thermally critical interconnects, a CMP fill-based cooling solution is presented by modifying the fill pattern in order to maximize heat dissipation within the BEOL. The resulting heat spreader (HS) design achieved up to 30% reduction in temperature for 10- $\mu \text{m}$ -wide interconnects and can reach 43% for narrower interconnects. The gained cooling makes it possible to extend the activation limits of interconnects by 15% and 25%, respectively. The experimentally validated HS simulation model is used to conduct parametric analysis for a range of interconnect dimensions with an eye on standardizing the HS design within the BEOL stage of ICs.

The Neodymium Stable Isotope Composition of the Oceanic Crust: Reconciling the Mismatch Between Erupted Mid-Ocean Ridge Basalts and Lower Crustal Gabbros

The trace element and isotopic compositions of mid-ocean ridge basalts (MORB) provide an important cornerstone for all studies seeking to understand mantle evolution. Globally there is a significant over-enrichment in the incompatible trace element concentrations of MORB relative to levels which should be generated by fractional crystallization. Thermal and geochemical constraints suggest that MORB require generation in open system magma chambers. However, the petrology of lower oceanic crustal rocks suggests instead that these enrichments maybe formed through reactive porous flow (RPF). Stable isotope compositions are process dependent and therefore provide an excellent mechanism to compare these contrasting models. This study presents the first neodymium (Nd) stable isotope compositions of Indian MORB and well characterized gabbroic rocks from the lower oceanic crust sampled at the Southwest Indian Ridge (Hole 735B). Indian MORB is extremely homogenous with a mean δ146Nd of −0.025 ±0.005‰ which is identical to the composition of Pacific MORB. Despite significant variability in the source composition of MORB globally (i.e. 143Nd/144Nd) their indistinguishable δ146Nd compositions suggests they were homogenized through the same process along the global ridge network. In stark contrast, oceanic gabbros have δ146Nd ranging from −0.026‰ to −0.127‰, doubling the natural variability in Nd stable isotopes observed in terrestrial rocks. Clinopyroxene separates possess variable δ146Nd but are isotopically heavier than the gabbroic whole rocks at the same major element compositions. These large variations in δ146Nd cannot be generated solely by the fractionation or accumulation of clinopyroxene and/or plagioclase. Hole 735B preserves widespread evidence of RPF which could induce kinetic isotopes fractionation during crystal growth. In clinopyroxene kinetic isotope fractionations will only induce ca. 0.02‰ variations therefore several cycles of dissolution and reprecipitation of isotopic signatures at grain boundaries are required to explain the range of δ146Nd observed in the gabbros. Given the large disconnect between the average composition of the lower crust (δ146Nd = −0.076‰) and MORB globally and the evidence of limited melt extraction into the upper crust at Hole 735B it is highly unlikely that the melts involved in RPF contributed in a substantial way to the Nd isotope composition of erupted MORB.

Activity niches outperform thermal physiological limits in predicting global ant distributions

AbstractAimThermal physiology is commonly used in mechanistic models to predict species distribution and project distribution change. Such thermal constraints for ants are often measured under laboratory conditions as critical thermal limits (CTmax and CTmin), but have also been observed in the field as foraging thermal limits (FTmin and FTmax). Here we compared distribution projections based on ant physiological and behavioural thermal limits with their realized distributions to assess the validity of using ecophysiological models to predict species ranges over large scales.LocationGlobal.TaxonAnts.MethodsFrom published literature, we compiled a database of 148 lab‐measured critical thermal limits and 137 field‐observed foraging thermal limits for 20 ant genera distributed around the world. We projected their potential ranges using active hour thresholds by matching their thermal limits or preferred thermal breadth (incorporating thermal optima) with hourly surface temperature data. We then compared the projections against a comprehensive global database of ant distributions to assess the validity of physiologically and behaviourally based models.ResultsWe found that surface temperature plays a clear role in generic‐level ant biogeography. Projections based on foraging thermal limits were more conservative in constraining ranges to observed distributions, while projections based on critical thermal limits often overestimated ranges. Furthermore, thermal limit models can be improved by incorporating behaviourally derived thermal optima.Main conclusionsOur results suggest that temperature‐dependent activity niches and thermal optima better reveal species realized thermal niches than critical thermal limits, and hence can improve predictions of species distributions and future distribution changes under climate change.

Comprehensive Finite Element Modeling for Pulsed Magnet Design Using COMSOL and Java

Ultra-high field pulsed magnets must simultaneously satisfy a number of often competing electrical, electromagnetic, structural, thermal, and economic constraints. To produce the highest field possible, nondestructive pulsed magnets are designed to operate at the limits of mechanical strength and electrical capacity of conductors. In this presentation, we will introduce a coupled multi-engineering finite element method (FEM) implemented in COMSOL Multiphysics package for detailed and accurate calculations of the mechanical, thermal and electromagnetic performances in entire longitudinal cross-section of the pulsed magnet. These transient FEM simulations are performed for entire pulse length and take into account the temperature and magnetic field dependences of electrical conductivity and mechanical properties of all the materials to provide better accuracy. Application Programming Interface (API) feature of COMSOL was used to automate repetitive modeling steps to significantly reduce the necessary time to create FEM models for a pulsed magnet which may consists up to thousands of turns and insulation/reinforcement layers. Computational results for our signature 100T non-destructive pulsed magnet will be presented.

Enhancing the mechanical and thermophysical properties of highly oriented graphite flake composites by formation of a uniform three dimensional tungsten carbide skeleton reinforcement

Tungsten carbide (WC) reinforced highly oriented graphite flake composites were obtained using a combined process of surface-coating and spark plasma sintering techniques. Uniform and continuous three-dimensional WC skeleton was formed in the samples with WC concentration higher than 7 vol%, rendering the resulting dense composites light, mechanical strong, high thermal conductive and with low thermal expansion. The skeleton architecture played a role of thermal expansion constraint which remarkably reduced the thermal expansion from 28 × 10−6 K−1 for highly oriented graphite matrix to ~5 × 10−6 K−1 for the composite with 26 vol% WC in the direction parallel to the sintering pressure. Concurrently, the composite with 26 vol% WC exhibited bending strength up to ~95 MPa, thermal conductivity up to ~381 W·m−1·K−1 in direction perpendicular to the sintering pressure. The created highly oriented graphite-based composites with uniform 3D ceramic reinforcement are expected to be applied in thermal management of current demanding situation.

ELECTRICITY INDUSTRIAL ORGANIZATION: WHAT ABOUT THE STRATEGIC BEHAVIOR OF HYDRO AND THERMAL OPERATORS?

In this paper, we develop a two-period model where we analyze and compare a hydro/thermal electrical system under different industrial organization: monopoly, Cournot competition and collusion; under storage constraint, water availability constraint and thermal turbine capacity constraint. First, we prove that the technological complementarity has an important role in satisfying electricity demand in the different industrial organizations. Second, we show by the analytical resolution, that intertemporal private monopoly water transfer from off-peak season to peak season is not as high as the same transfer under a public monopoly and therefore this increases the market price. Under Cournot competition, an increase in the peak season demand implies a water transfer strategy from off-peak to peak season. The results of collusion show that the electricity price is less dependent on the hydropower capacity. Keywords : Electricity market; Monopoly; Competition; Collusion; Hydro; Thermal. JEL Classifications : L20; Q40; Q25. DOI: https://doi.org/10.32479/ijeep.8775

Night conditions affect morning incubation behaviour differently across a latitudinal gradient

Intermittently incubating birds alternate between sessions of egg warming and recesses for foraging during the day, but stay on the nest continuously at night. Hence, energy costs of nocturnal incubation (which increase during longer and colder nights) cannot be replenished until the next day. Night conditions might therefore be expected to affect morning incubation behaviour the day after. We tested this prediction by exploring latitudinal and seasonal trends in characteristics of the first recess in Eastern Bluebirds Sialia sialis over a 1400‐km latitudinal gradient in the continental USA. The time from civil dawn to leaving the nest (latency) increased with latitude early in the breeding season but decreased with latitude late in the season. Birds breeding at higher latitudes also took longer first recesses throughout the season, which led to a larger drop in nest temperature. At the local scale, birds rose earlier after longer nights if the night was also cold, but night length did not predict latency following warm nights. The first recess was longer if the night was warmer, probably because birds could replenish reserves at lower risk of low egg temperature. Our study shows that characteristics of the night led to behavioural changes in features of early morning incubation that were evident at both continental and local scales. These responses also affected nest temperature. Hence, night conditions carry over to incubation behaviour the following morning, which in turn may impose thermal constraints on embryonic development.

Runtime Performance Optimization of 3-D Microprocessors in Dark Silicon

Because the increasing power density is limited by the thermal constraint, multi-core integrated systems have stepped into the dark silicon era recently, meaning not all parts of the system can be powered on at the same time. Dark silicon effects are, especially severe for 3-D microprocessors due to the even higher power density caused by the stacked structures, which greatly limit the system performances. In this article, we propose a greedy based core-cache co-optimization algorithm to optimize the performance of 3-D microprocessors in dark silicon at runtime. The new method determines many runtime settings of the 3-D system on the fly, including the active core and cache bank positions, active cache bank number, and the voltage/frequency (V/f) level of each active core, which optimizes the performance of the 3-D microprocessor under thermal constraint. Because the core-cache settings are co-optimized in the 3-D space and the power budgets are computed dynamically according to the running state of the 3-D microprocessor, the new method leads to a higher system performance compared with the existing methods. Experiments on two 3-D microprocessors show the greedy-based core-cache co-optimization algorithm outperforms the state-of-the-art 3-D dark silicon microprocessor performance optimization method by achieving a higher processing throughput with guaranteed thermal safety.

Hatchling Emergence Ecology of Ouachita Map Turtles (Graptemys ouachitensis) on the Lower Wisconsin River, Wisconsin

Despite its biological importance in shaping both individual fitness and population structure, much remains to be learned about the hatchling emergence ecology of most freshwater turtles. Here, we provide some of the first details on these early life stages for the Ouachita map turtle (Graptemys ouachitensis) obtained during 2015–2017 along the lower Wisconsin River, Iowa County, Wisconsin, and integrate our results into related research within the genus Graptemys. Dedicated trail cameras over in situ turtle nests provided otherwise difficult to obtain observational data relevant to natural hatchling emergence without disturbing nests or hatchlings. In contrast to some earlier reports for Graptemys, hatchling emergence was mostly diurnal and synchronous, primarily in the morning soon after soil temperatures began to rise from overnight low values. Data suggest a temperature change model of cueing hatchling emergence, which may represent a local or regional adaptation to reduce nocturnal predation risks, mostly from raccoons (Procyon lotor), or may simply reflect default diurnal hatchling activity patterns when not affected by thermal constraints. Aside from predation, hatchlings on this small study site are affected by vegetative shading, leading to relatively long times to first emergence periods (mean, 82.3 d), low mean nest temperatures (25.9°C), and a likely male-biased sex ratio. These findings highlight the value of hatchling emergence studies in revealing important influences on population viability and in guiding appropriate habitat management in conservation efforts.

Analysis and elimination of noise-induced temperature error in processor thermal control

Processor thermal control in real-time systems is crucial because overheated processors may result in critical performance degradation or even system failure. The main challenges in processor thermal control in real-time systems are as follows: (i) the need to satisfy both real-time and thermal constraints; (ii) uncertain system dynamics; and (iii) thermal sensor noise. The first two issues have been resolved in substantial studies while the issue of sensor noise has not been thoroughly addressed. In this paper, we experimentally identify that even a small zero-mean sensor noise can induce a significant steady-state error in processor thermal control. This steady-state temperature error is contrary to the intuition that zero-mean sensor noise normally induces zero-mean fluctuations around the target temperature. We rigorously analyze the phenomenon based on the stochastic averaging theory and quantify the error in a closed form in terms of noise statistics and system parameters. We propose a thermal control architecture for effectively eliminating the thermal error and tightly controlling the processor temperature. Through extensive experiments, we validate the proposed architecture.