Transport Time Scales Research Articles

Argon doped pellets for fast and efficient radiative power removal in ASDEX Upgrade

Argon doped deuterium pellets with about 1 per mille Ar atomic fraction have been injected into ASDEX Upgrade H-mode discharges and demonstrate fast and efficient power removal from the outer plasma region. Bolometer views directly on the pellet and in its very close vicinity observe a strong, non-toroidally symmetric radiation pattern on a fast, sub-ms time scale. This pattern is explained by the ionisation process of the delivered Ar neutrals, leading to non-coronal radiation by intermediate ionisation stages until the equilibrium He like stage is reached. Subsequently, a toroidally symmetric radiation increase is observed with a fast initial decay time of about 20 ms consistent with the radial particle transport time scale for a source located in the outer plasma. In the following, a radiation pattern related to Ar recycling develops comparable to the pattern observed with Ar midplane gas puffing which decays with the Ar divertor pumping time of about 200 ms. The energy radiated around each pellet is described by the radiative potential of Ar evaluated for non-coronal conditions with the ablation time as the relevant time scale. A factor 4 too low radiated energy is obtained by this simple model, which could be explained by stronger deviations from corona equilibrium and plasma parameter variations in the vicinity of the pellet. Injection of Ar-doped pellets into a no-ELM quasi-continuous exhaust H-mode discharge showed no triggering of ELMs by the pellet. Advantages of the pellet seeding scheme are the faster reaction time of the radiation compared to gas puffing, which may be important to counter-act transient re-attachment in ITER or in a reactor and an elevated radiative efficiency in the outer core plasma due to non-corona effects.

The Fate of Oxygen in the Ocean and Its Sensitivity to Local Changes in Biological Production

AbstractWe investigate the sensitivity of the oxygen content and true oxygen utilization of key low‐oxygen regions Ω to pointwise changes in biological production. To understand how the combined water and biogenic particle transport controls the sensitivity patterns and the fate of oxygen in the ocean, we develop new relationships that link the steady‐state oxygen content and deficit of Ω to the downstream and upstream oxygen utilization rate (OUR), respectively. We find that the amount of oxygen from Ω that will be lost per unit volume at point r is linked to OUR(r) through the mean oxygen age accumulated in Ω. The geographic sensitivity pattern of the Ω‐integrated oxygen deficit is shaped by where the utilization occurs that causes this deficit. The contribution to the oxygen deficit of Ω from utilization at r is controlled by the mean time that water at r spends in Ω before next ventilation at the surface. We illustrate these relationships and the new transport timescales using a simple steady‐state data‐constrained carbon and oxygen model. We focus on Ω being the global ocean, the Pacific Hypoxic Zone (PHZ, [O2] < 62.5 µM), and the North Pacific oxygen minimum zone. The oxygen deficit of the PHZ is most sensitive where mode and intermediate waters form and where increased organic‐matter production directly increases the PHZ's oxygen demand. The fraction of the local oxygen concentration that will be utilized in respiration is as high as 90% in the PHZ and up to 70% in the water column beneath it.

Water Circulation and Transport Time Scales in the Beagle Channel, Southernmost Tip of South America

The Beagle Channel is a long and narrow interoceanic passage within the Tierra del Fuego archipelago in the southernmost tip of South America. A high-resolution 3D hydrodynamic model based on the finite elements method was applied to investigate the residual circulation, water fluxes and transport time scales inside this channel. Numerical solutions were analyzed at seasonal time scale and the model results compared with observed ocean data. The circulation pattern is characterized by a west-to-east residual flow with low intensity and low seasonal variability. The water fluxes through the channel were estimated to be, on average, around 12,700 m3/s, with inflow through its western entrance and eastwards outflow mainly through the Mackinlay Strait. The water residence times vary seasonally with basin averages between 36 and 43 days and maximum values between 53 and 95 days. The results provide an overview of the hydrodynamics and water residence times in the Beagle Channel, a unique ecosystem threatened by recent anthropogenic pressures and climate change.

Controls on surface distributions of dissolved organic carbon and nitrogen in the southeast Pacific Ocean

Here we use data from three meridional survey cruises that took place in 1994, 2007/2008 and 2016/2017 in the southeast Pacific Ocean to investigate controls on surface distributions of dissolved organic carbon and nitrogen (DOC and DON, respectively). While DOC and DON production occur simultaneously in the euphotic layer of the gyre margins, budgets that account for horizontal transport, production and consumption are not balanced across the region. Our results show that while DOC concentrations increase inside the gyre, DON remains at similar levels in comparison to margins. There is little interannual variability in DOC and DON trends, except near the equator, explained by ENSO phases and seasonality. While the effect of evaporation (precipitation) did not significantly contribute to variable DOC and DON concentrations, differences in the naturally occurring 15N/14N isotope ratios from the most recent cruise suggest net consumption of allochthonous DON inside the gyre. In the northernmost and southernmost stations, where surface [NO3−] was detected, 15N-DON showed low signatures in the upper 300 m of 3.8 ± 1.5‰ and 2.5 ± 1.6‰, respectively. Inside the gyre where [NO3−] was undetectable, higher values averaging 5.0 ± 0.9‰ were observed. This suggests that a fraction of DON turns over more rapidly than the time scale of horizontal transport, with the isotopic change reflecting the gradient in 15N-DON of newly produced organic matter. Thus, allochthonous DON is likely a significant source of nitrogen to microbial communities inside this nitrogen-limited environment and should be taken into consideration when closing nutrient budgets to estimate productivity in the South Pacific Subtropical Gyre.

Boosting Efficiency in Light‐Driven Water Splitting by Dynamic Irradiation through Synchronizing Reaction and Transport Processes**

This work elaborates the effect of dynamic irradiation on light‐driven molecular water oxidation to counteract deactivation. It highlights the importance of overall reaction engineering to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogeneous three‐component ruthenium‐based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 31 referring to the external energy efficiency by controlling the local availability of photons. Detailed insights into the mechanism of light driven water oxidation could be obtained using complementary methods of investigation like Raman, IR, and UV/Vis/emission spectroscopy, unraveling the importance of avoiding high concentrations of excited photosensitizers.

Sediment Residence Times in Large Rivers Quantified Using a Cosmogenic Nuclides Based Transport Model and Implications for Buffering of Continental Erosion Signals

AbstractThe weathering of continental surfaces and the transport of sediments via rivers into the oceans is an integral part of the dynamic processes that shape the Earth's surface. To understand how tectonic and climatic forcings control regional rates of weathering, we must be able to identify their effects on sedimentary archives over geologic timescales. Cosmogenic nuclides are a valuable tool to study rates of surface processes and have long been applied in fluvial systems to quantify basin‐wide erosion rates. However, in large rivers, continual processes of erosion and deposition during sediment transport make it difficult to constrain how long sediments spend within the fluvial system. In this study, we examine the role of rivers in buffering erosional signals by constraining the timescales of fluvial transport in large rivers across the world. We apply a stochastic numerical model based on measurements of cosmogenic nuclides concentrations and calculate sediment residence times of 104–105 years in large rivers. These timescales are equal to or longer than climatic cycles, implying that changes to rates of erosion brought on by climatic variations are buffered during transport in large rivers and may not be recognizable in the sedimentary record.

On the molecular mechanism behind the bubble rise velocity jump discontinuity in viscoelastic liquids

Bubbles rising in viscoelastic liquids may exhibit a jump discontinuity of the rise velocity as a critical bubble volume is exceeded. The phenomenon has been extensively investigated in the literature, both by means of experiments as well as via numerical simulations. The occurrence of the velocity jump has been associated with a change of the bubble shape under the formation of a pointed tip at the rear end and to the appearance of a so-called negative wake with the liquid velocity behind the bubble, pointing in the opposite direction to that in viscous Newtonian fluids. We revisit this topic, starting with a review of the state of knowledge on the interrelations between the mentioned characteristic features. In search for a convincing explanation of the jump phenomenon, we performed detailed numerical simulations of the transient rise of single bubbles in 3D, allowing for a local polymer molecular conformation tensor analysis. The latter shows that polymer molecules traveling along the upper bubble hemisphere are stretched in the circumferential direction, due to the flow kinematics. Then, depending on the relaxation time scale of the polymer, the stored elastic energy is either unloaded essentially above or below the bubble's equator. In the former case, this slows down the bubble, while the bubble gets accelerated otherwise. In this latter case, the relative velocity of the polymer molecules against the bubble is increased, giving rise to a self-amplification of the effect and thus causing the bubble rise velocity to jump to a higher level. Detailed experimental velocity measurements in the liquid field around the bubble confirmed the conclusion that the ratio of the time scale of the Lagrangian transport of polymer molecules along the bubble contour to the relaxation time scale of the polymer molecules determines the sub- or supercritical state of the bubble motion.

Benthic Biolayer Structure Controls Whole‐Stream Reactive Transport

AbstractHyporheic zone reaction rates are highest just below the sediment‐water interface, in a shallow region called the benthic biolayer. Vertical variability of hyporheic reaction rates leads to unexpected reaction kinetics for stream‐borne solutes, compared to classical model predictions. We show that deeper, low‐reactivity locations within the hyporheic zone retain solutes for extended periods, which delays reactions and causes solutes to persist at higher concentrations in the stream reach than would be predicted by classical approaches. These behaviors are captured by an upscaled model that reveals the fundamental physical and chemical processes in the hyporheic zone. We show how time scales of transport and reaction within the biolayer control solute retention and transformation at the stream scale, and we demonstrate that accurate assessment of stream‐scale reactivity requires methods that integrate over all travel times.

Vertical Transport Timescale of Surface‐Produced Particulate Material in the Chesapeake Bay

AbstractAccumulation and remineralization of surface‐produced particulate organic matter (POM) in the water column and seabed link closely to hypoxia and the health of aquatic ecosystems. The POM retention time provides a key timescale to interpret biochemical reaction processes. In this study, we investigated the spatiotemporal variations in the vertical particulate age (VPA) of surface‐produced POM, which is the mean time elapsed since the particulates last contact the surface, by incorporating major physical processes including sinking, resuspension, and deposition in the Chesapeake Bay. It was found that the vertical transport time for the particulates (i.e., VPA) is much longer than the dissolved counterparts as the former consists of new material from the surface and the resuspended aged material that has elongated resting on the seabed after deposition. The VPA is sensitive to settling velocity, especially in low‐frequent resuspension environments, and varies over 2 orders of magnitude with settling velocity from 0 to 10 m/day. Slow‐sinking material can remain in suspension and seldom settle to the seabed, thus mainly contribute to pelagic processes, while the fast‐sinking material connects closely with benthic processes. The seasonality of VPA decreases as the settling velocity increases. No significant difference in VPA was found between wet and dry years, yet the episodic strong flood events entrain old materials from the depositional lateral shoals to increase VPA in the channel. The transport age bridges cross disciplinaries by providing the fourth‐dimensional age information as a common currency to compare the physical transport timescale with the timescales for biochemical reactions.

Exploration of Ion Transport in Blends of an Ionic Liquid and a Polymerized Ionic Liquid Graft Copolymer.

In this study, we prepared a composite membrane consisting of a poly(1-butyl-3-vinylimidazolium-tetrafluoroborate) (poly([BVIM]-[BF4])) polymerized ionic liquid graft copolymer (PILGC) and a blend of PILGC and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]-[BF4]) ionic liquid (IL) to explore techniques for improving the conductivity of PILGCs, which is normally three orders of magnitude lower than that of ILs. PILGCs, which are environmentally friendly, have attracted much interest. To gain a better understanding of ion transport in composites, the mechanisms of ion transport in composite components should be explored. We investigated anion transport in ILs and PILGCs and were able to obtain the correct ion transport mechanisms in IL-PILGC blends based on a previous work. We performed molecular dynamics (MD) simulations, which are commonly used to investigate molecular mechanisms. According to the MD simulation results, in most IL-PILGC blends of various compositions, the contributions of cations are greater than those of anions. This is one reason that blends have higher conductivities than their component PILGCs. To the best of our knowledge, we are the first to identify ion transport mechanisms in PILGCs and their blends with ILs by exploring subdiffusive ion motion regimes. The ratio of the number of cages with more than three cationic branch chains in the blend with 50 wt % PILGC, the blend with 80 wt % PILGC, and the PILGC was 0.26:0.39:0.65. Therefore, the ratio of firm cages gets a promotion as the PILGC content increases. Because the ratio of fast ions decreases as the ratio of firm cages increases, the blend with 80 wt % PILGC has lower anion diffusivities than the blend with 50 wt % PILGC. It was inappropriate to probe ion transport in PILGCs (or IL-PILGC blends) solely via analyzing ion association interactions. Analysis of only ion association interactions led to the incorrect conclusion that the time scales of ion transport in PILGCs are given by the continuous ion association time, which is the time when the ion association remains paired rather than the time when an ion is caught inside a cage. Proper methods should be used to obtain more accurate theories.

Shelf Transport Pathways Adjacent to the East Australian Current Reveal Sources of Productivity for Coastal Reefs

The region where the East Australian Current (EAC) separates from the coast is dynamic and the shelf circulation is impacted by the interplay of the western boundary current and its eddy field with the coastal ocean. This interaction can drive upwelling, retention or export. Hence understanding the connection between offshore waters and the inner shelf is needed as it influences the productivity potential of valuable coastal rocky reefs. Near urban centres, artificial reefs enhance fishing opportunities in coastal waters, however these reefs are located without consideration of the productivity potential of adjacent waters. Here we identify three dominant modes of mesoscale circulation in the EAC separation region (~31.5−34.5°S); the ‘EAC mode’ which dominates the flow in the poleward direction, and two eddy modes, the ‘EAC eddy mode’ and the ‘Eddy dipole mode’, which are determined by the configuration of a cyclonic and anticyclonic eddy and the relationship with the separated EAC jet. We use a Lagrangian approach to reveal the transport pathways across the shelf to understand the impact of the mesoscale circulation modes and to explore the productivity potential of the coastal waters. We investigate the origin (position and depth) of the water that arrives at the inner-mid shelf over a 21-day period (the plankton productivity timescale). We show that the proportion of water that is upwelled from below the euphotic zone varies spatially, and with each mesoscale circulation mode. Additionally, shelf transport timescales and pathways are also impacted by the mesoscale circulation. The highest proportion of upwelling (70%) occurs upstream of 32.5°S, associated with the EAC jet separation, with vertical displacements of 70–120 m. From 33 to 33.5°S, water comes from offshore above the euphotic layer, and shelf transport timescales are longest. The region of highest retention over the inner shelf is immediately downstream of the EAC separation region. The position of the EAC jet and the location of the cyclonic eddy determines the variability in shelf-ocean interactions and the productivity of shelf waters. These results are useful for understanding productivity of temperate rocky reefs in general and specifically for fisheries enhancements along an increasingly urbanised coast.

Radiocarbon in the Land and Ocean Components of the Community Earth System Model

AbstractLarge amounts of the carbon‐isotope 14C, entering Earth's carbon cycle, were produced in the atmosphere by atomic bomb tests in the 1950s and 1960s. Here, we forced the ocean and land components of the Community Earth System Model with atmospheric 14CO2 over the historical period to constrain overturning time scales and fluxes. The uptake of bomb 14C by the land model is lower than observation‐based estimates. This mismatch is likely linked to too‐low 14C uptake by vegetation as the model overestimates 14C/C ratios of modern soils. This suggests model biases in forest productivity or wood carbon allocation and turnover, and, in turn, a bias in the forest sink of anthropogenic carbon. The ocean model matches the observation‐based global bomb 14C inventories when applying the quadratic relationship between gas transfer piston velocity and wind speed of Wanninkhof (2014), https://doi.org/10.4319/lom.2014.12.351 and the wind products from Large and Yeager or the Japanese Reanalysis Project. Simulated natural radiocarbon ages in the deep ocean are many centuries older than data‐based estimates, indicating too slow deep ocean ventilation. The sluggish circulation causes large biases in biogeochemical tracers and implies a delayed deep ocean uptake of heat and carbon in global warming projections. Our study suggests that 14C observations are key to constrain carbon fluxes and transport timescales for improved representations of land and ocean biogeochemical cycles and Earth system model projections.

Brief communication: Lower-bound estimates for residence time of energy in the atmospheres of Venus, Mars and Titan

Abstract. The residence time of energy in a planetary atmosphere, τ, which was recently introduced and computed for the Earth's atmosphere (Osácar et al., 2020), is here extended to the atmospheres of Venus, Mars and Titan. τ is the timescale for the energy transport across the atmosphere. In the cases of Venus, Mars and Titan, these computations are lower bounds due to a lack of some energy data. If the analogy between τ and the solar Kelvin–Helmholtz scale is assumed, then τ would also be the time the atmosphere needs to return to equilibrium after a global thermal perturbation.

Timescales of magma transport in the Columbia River flood basalts, determined by paleomagnetic data

Flood basalts represent major events in Earth History, in part because they are linked to large climate perturbations and mass extinctions. However, the durations of individual flood basalt eruptions, which directly impact potential environmental crises, are poorly constrained. Here we use a combination of paleomagnetic data and thermal modeling to create a magnetic geothermometer (MGT) that can constrain the active transport lifetime of magmatic conduits and intrusions. We apply the MGT technique to eight feeder dike segments of the Columbia River basalts (CRB), demonstrating that some dike segments were actively heating host rocks for less than one month, while other segments may have been active for several years. Results suggest that eruption rates, localized spatially along-strike of dike segments, were as high as 1–8 km3day−1. These results help contextualize field evidence for contrasting CRB eruption durations and suggest a pathway for constraining the tempo of global flood basalt magmatism that is beyond the resolution of geochronology.

Process-Dependent Solute Transport in Porous Media

Solute transport under single-phase flow conditions in porous micromodels was studied using high-resolution optical imaging. Experiments examined loading (injection of ink-water solution into a clear water-filled micromodel) and unloading (injection of clear water into an ink-water filled micromodel). Statistically homogeneous and fine-coarse porous micromodels patterns were used. It is shown that the transport time scale during unloading is larger than that under loading, even in a micromodel with a homogeneous structure, so that larger values of the dispersion coefficient were obtained for transport during unloading. The difference between the dispersion values for unloading and loading cases decreased with an increase in the flow rate. This implies that diffusion is the key factor controlling the degree of difference between loading and unloading transport time scales, in the cases considered here. Moreover, the patterned heterogeneity micromodel, containing distinct sections of fine and coarse porous media, increased the difference between the transport time scales during loading and unloading processes. These results raise the question of whether this discrepancy in transport time scales for the same hydrodynamic conditions is observable at larger length and time scales.

Nitrate Transport and Retention in Western European Catchments Are Shaped by Hydroclimate and Subsurface Properties

AbstractExcess nitrogen (N) from anthropogenic sources deteriorates freshwater resources. Actions taken to reduce N inputs to the biosphere often show limited or only delayed effects in receiving surface waters hinting at large legacy N stores built up in the catchments' soils and groundwater. Here, we quantify transport and retention of N in 238 Western European catchments by analyzing a unique data set of long‐term N input and output time series. We find that half of the catchments exhibited transport times with an average riverine concentration peak arriving 5 years after application. Longer transport times were evident in catchments with high potential evapotranspiration and low precipitation seasonality. On average the catchments retained 72% (Interquartile Range: 18%) of the N from diffuse sources with retention efficiency being specifically high in catchments with low discharge and thick, unconsolidated aquifers. The estimated transport time scales do not explain the observed N retention, suggesting a dominant role of biogeochemical legacy in the catchments' soils rather than a legacy store in the groundwater. Future water quality management should account for the accumulated biogeochemical N legacy by fostering denitrifying conditions or soil N recycling to avoid long‐term leaching and water quality deteriorations for decades to come.

An assessment of residence and influence times in Xiamen Bay, China

Water transport time scales are important indicators to assess the renewal of substance inside coastal embayments. Estimates of water renewal efficiency represented by residence and influence times in Xiamen Bay were made via a series of numerical experiments, using the instantaneous tracer injection method. It was found that the average e-folding threshold residence time in the bay is approximately 16.5 days, and that the residence time increases near the entrances to land because water exchange between the bay and the Taiwan Strait is the dominant water-renewal process. The seawater influence time has a similar spatial distribution to the residence time. The freshwater influence time is much shorter in the western region of the bay than in the eastern region, which shows that the influence of Jiulong River freshwater is largely restricted to the western region. The changes in the residence and influence times reveal that increased river discharge mainly accelerates water renewal in the western region of the bay, whereas increased tides mainly accelerate water renewal in the eastern region and the northern part of the western region. The drivers of water renewal were examined using effective transport velocities that were defined based on the decomposition of tracer flux, and showed that tidal residual flow determines the extent of water renewal in Xiamen Bay. The estimation of residence time is sensitive to the operation of instantaneous method. The release of tracer at spring tide results in a shorter residence time and the use of a small threshold can improve the consistency of estimated threshold residence times.

Microplastics and nanoplastics barely enhance contaminant mobility in agricultural soils

Farmland soils are prone to contamination with micro- and nanoplastics through a variety of agricultural practices. Concerns are recurrently raised that micro- and nanoplastics act as vector for organic contaminants to deeper soil layers and endanger groundwater resources. Whether and to what extent micro- and nanoplastics facilitate the transport of organic contaminants in soil remains unclear. Here we calculated the ratio between transport and desorption time scales using two diffusion models for micro- and nanoplastics between 100 nm and 1 mm. To identify micro- and nanoplastics bound contaminant transport we evaluated diffusion and partitioning coefficients of prominent agrochemicals and additives and of frequently used polymers e.g., polyethylene and tire material. Our findings suggest that the desorption of most organic contaminants is too fast for micro- and nanoplastics to act as transport facilitators in soil. Contaminant transport enabled by microplastics was found to be relevant only for very hydrophobic contaminants (logKow >5) under preferential flow conditions. While micro- and nanoplastics might be a source of potentially harmful contaminants in farmland soils this study suggests that they do not considerably enhance contaminant mobility.

Sensitivities of Porous Beds and Plates to Ignition by Firebrands

The increasing occurrence of severe wildfires, coupled with the expansion of the wildland urban interface has increased the number of structures in danger of being destroyed by wildfires. Ignition by firebrands is a significant avenue for fire spread and structure loss; thus, understanding processes and parameters that control the ignition of fuel beds by firebrands is important for reducing these losses. In this study the effect of fuel bed characteristics (i.e., particle size and porous or solid fuel bed) on ignition behavior was considered. Modelling and analysis was conducted to better understand parameters that are dominant in controlling ignition. The fuel beds, made from Douglas-fir shavings, Douglas-fir plates, or cardboard plates, were heated with a cartridge heater (i.e., surrogate firebrand) to observe ignition. Smaller particles were observed to ignite more readily in porous beds than larger particles when heat transfer from the heater is primarily through conduction. This occurs in large part due to differences in contact area between the fuel bed and the heater coupled with thermal properties of the fuel bed. As particle sizes increased, ignition was more likely to occur at extended times (>100 s) due to the increased importance of radiation heat transfer. Douglas-fir plates were primarily observed to ignite at times where conduction was the dominant mode of heat transfer (<10 s). Heat flux delivered to the fuel bed was observed to be a more accurate predictor of ignition likelihood and ignition time than heater temperatures. The characteristic ratio of transport and chemical timescales can be used, in conjunction with the measured heat flux and thermal diffusivity of the fuel beds, as a first approximation to predict ignition for the porous fuel beds. This suggests that future work focusing on these parameters may produce a general characterization of fuel bed ignition probability across fuel beds materials and morphologies.

A General and Predictive Understanding of Thermal Transport from 1D- and 2D-Confined Nanostructures: Theory and Experiment.

Heat management is crucial in the design of nanoscale devices as the operating temperature determines their efficiency and lifetime. Past experimental and theoretical works exploring nanoscale heat transport in semiconductors addressed known deviations from Fourier’s law modeling by including effective parameters, such as a size-dependent thermal conductivity. However, recent experiments have qualitatively shown behavior that cannot be modeled in this way. Here, we combine advanced experiment and theory to show that the cooling of 1D- and 2D-confined nanoscale hot spots on silicon can be described using a general hydrodynamic heat transport model, contrary to previous understanding of heat flow in bulk silicon. We use a comprehensive set of extreme ultraviolet scatterometry measurements of nondiffusive transport from transiently heated nanolines and nanodots to validate and generalize our ab initio model, that does not need any geometry-dependent fitting parameters. This allows us to uncover the existence of two distinct time scales and heat transport mechanisms: an interface resistance regime that dominates on short time scales and a hydrodynamic-like phonon transport regime that dominates on longer time scales. Moreover, our model can predict the full thermomechanical response on nanometer length scales and picosecond time scales for arbitrary geometries, providing an advanced practical tool for thermal management of nanoscale technologies. Furthermore, we derive analytical expressions for the transport time scales, valid for a subset of geometries, supplying a route for optimizing heat dissipation.