Transient Conduction Research Articles

High resolution optical mapping of cardiac electrophysiology in pre-clinical models

Optical mapping of animal models is a widely used technique in pre-clinical cardiac research. It has several advantages over other methods, including higher spatial resolution, contactless recording and direct visualisation of action potentials and calcium transients. Optical mapping enables simultaneous study of action potential and calcium transient morphology, conduction dynamics, regional heterogeneity, restitution and arrhythmogenesis. In this dataset, we have optically mapped Langendorff perfused isolated whole hearts (mouse and guinea pig) and superfused isolated atria (mouse). Raw datasets (consisting of over 400 files) can be combined with open-source software for processing and analysis. We have generated a comprehensive post-processed dataset characterising the baseline cardiac electrophysiology in these widely used pre-clinical models. This dataset also provides reference information detailing the effect of heart rate, clinically used anti-arrhythmic drugs, ischaemia-reperfusion and sympathetic nervous stimulation on cardiac electrophysiology. The effects of these interventions can be studied in a global or regional manner, enabling new insights into the prevention and initiation of arrhythmia.

Role of quenching method on cooling rate and microstructure of steels: Variations in coolant and its flow arrangement

During quenching of steel, the rate of heat removal from the surface and the local cooling rate of steel determine its microstructure. Here these rates are controlled by the extent of the force flow (e.g., single and multiple jets, forced and unforced immersion), coolant (e.g., water and oil), and steel (e.g., stainless or alloy). The steel plate is initially at 900°C is cooled with room-temperature coolants. The recorded temperature distribution within the object is used to compute the surface temperature and heat flux by solving the inverse heat conduction problem (IHCP). The high Biot number analytic solution of 1-D transient conduction in semi-infinite slab with prescribed surface temperature is also used as a reference for the ideal cooling condition. It is shown that the multiple water jet cooling results in the highest heat transfer rate (largest Biot number) and cooling rate, thus the desired martensite phase of the microstructure. On the other hand, the water forced immersion, water immersion, and oil immersion have a progressively lower cooling rate (smaller Biot number), and therefore, a smaller fraction of the martensite phase. Comparison of the IHCP and analytic results for the multiple water jets show that the IHCP underpredicts the cooling rate for the first 0.5 s.

Modeling Thermal Behavior of Mass Concrete Structures at Early Age

In this study, a three-dimensional (3D) mathematical model based on conduction heat transfer in a solid is developed to predict the temperature profile of large concrete elements during the hydration process at early ages. Four different concrete mix designs are tested in the laboratory and on site. Heat of hydration and activation energy of each concrete mix is determined in the laboratory and temperature dependent thermo-physical parameters are considered in the simulations. The transient 3D conduction heat transfer equation with a heat generation source term is discretized by using finite volume method. The mathematical model is validated with temperature-time histories measured from four 1.8 m cube concrete blocks that are cast on site. Results obtained from the 3D model show that variable thermal properties are considered to accurately predict the temperature gradients. According to the analysis, the numerical model demonstrates that it can produce accurate predictions for temperature analysis within the 1.8 m large concrete elements.

Simultaneous laser-induced fluorescence, particle image velocimetry and infrared thermography for the investigation of the flow and heat transfer characteristics of nucleating vapour bubbles

Boiling is an effective heat removal process, used for heat exchange and thermal management purposes in many technological applications, from the scale of microelectronic devices to nuclear reactors. However, the physical mechanisms involved in this process are not fully understood yet due to the complexity that arises from the many interacting underlying sub-processes involved in the nucleation, growth and detachment of bubbles that occur during the process. Here, we present an advanced methodology based on combined, synchronized high-speed infrared (IR) thermometry, ratiometric two-colour laser-induced fluorescence (2cLIF) and particle image velocimetry (PIV), along with sample results of an experimental investigation conducted in deionized water, aimed at elucidating the mechanisms involved in the bubble lifecycle. IR thermometry is used to measure the time-dependent 2-D temperature and heat flux distributions over a boiling surface, and 2cLIF is used to measure the time-dependent temperature-field in a vertical plane, in the liquid phase around developing bubbles. Furthermore, PIV is used to measure the velocity fields around the bubbles, in the same plane as 2cLIF. The investigation reveals and allows us to quantify fundamental heat transfer aspects such as the contribution of triple contact line evaporation to the bubble growth process, the dynamics of the near-wall superheated liquid layer, the mixing effect produced by bubble growth and departure, convection effects around the bubble, and quenching heat transfer. Specifically, we observe that, in our experiment, with slowly growing bubbles, the microlayer does not form, and the evaporation at the solid-liquid-vapour contact line contributes to approximately one third of the total heat transferred to the bubble. We also observed that the fluid that rewets the dry spot at the bubble base, as the bubble departs from the boiling surface, comes from the near-wall superheated thermal boundary layer adjacent to the bubble, i.e., it is warmer than the fluid in the bulk. We confirm this finding by modelling this quenching heat transfer phase as a transient conduction process.

Hearing Outcomes of Transmastoid Plugging for Superior Canal Dehiscence Syndrome by Underwater Endoscopic Surgery: With Special Reference to Transient Bone Conduction Increase in Early Postoperative Period.

To investigate the influence on hearing of transmastoid plugging of the superior semicircular canal accompanied with membranous superior canal transection by underwater endoscopic ear surgery (UWEES) for the superior semicircular canal dehiscence syndrome. Retrospective case review. Tertiary referral center. Seven patients underwent plugging with membranous superior canal transection with UWEES from 2017 to 2019. Bone conduction (BC) thresholds (250, 500, 1000, 2000, 4000 Hz) were repetitively examined in early postoperative period. Subjective symptoms and pure-tone audiometry. Transient BC threshold increase was detected in all cases in early postoperative period and hearing levels were ameliorated in 1 to 2 months. The mean maximum BC threshold elevations (dB) during the early postoperative period (within 1 mo) and the postoperative stable hearing period (after 2 mo) were 18.6 and 2.9 at 250 Hz, 24.3 and 8.6 at 500 Hz, 26.4 and 8.6 at 1000 Hz, 28.6 and 7.1 at 2000 Hz, and 30.0 and 0.8 (except for scale-out cases) at 4000 Hz. respectively. The mean maximum BC thresholds in the early period were significantly elevated compared with those in the stable period at each frequency (p < 0.01). Hearing outcomes of transmastoid plugging with transection of the membranous superior canal by using UWEES were found favorable in a long-term follow-up. However, it caused transient reversible hearing loss in all cases. The BC increase in early postoperative period may not cause permanent hearing loss but improvement for the surgical technique may still be necessary.

Fuel Particle Heat Transfer Part 1: Convective Cooling of Irradiated Fuel Particles

ABSTRACT Wildfire spread requires fuel particles heated to ignition but the roles of radiation and convection heat transfer have not before been examined in detail. This paper reports on laboratory experiments and numerical modeling of wood particle response when subjected to a fixed radiant flux. The experiments used a propane-fueled radiant panel with an elliptical mirror system to focus a constant radiant flux on fuel particles of different sizes and cross-sectional shapes. Particle temperature was measured with fine-wire thermocouples embedded on the surface. Particle heating during free and forced convection with ambient air was found to depend on particle size, specifically the convective length of the irradiated surface. Ambient convection cooled 1 mm square particles sufficiently to prevent ignition but not 3 mm particles and larger. Surface area-to-volume ratio did not govern particle surface heating but did determine a particle’s thermal response rate. A finite difference, numerical method was developed to solve a two-dimensional, transient conduction model with radiative and convective boundary conditions. Model results were reliable when compared to experimental results and confirmed particle surface length (convection) as a principal determining factor governing fuel particle heating and fuel particle ignition.

Nanotexturing-enhanced heat transfer and interfacial evaporation for energy-efficient solar-thermal water desalination

Seawater desalination based on nano-interface-enhanced evaporation is one of the promising energy-effective solutions to alleviate global clean water scarcity. However, the heat and mass transfer mechanisms from the absorber surface to the surrounding liquid, which is critically significant to improve the evaporation performance in practical applications, are still unclear. Here, we develop an all-carbon hierarchical architecture via engineering of vertically oriented graphenes on a graphite felt monolith, and simultaneously, gain new insights into the effects of the surface morphology on the heat and mass transfer at the absorber/liquid interface by manipulating the graphene texturing from microscale to nanoscale. In the visualization experiments, compared with the microstructured and smooth surfaces, a higher-density bubble distribution with a smaller departure diameter on the nanostructured surface is observed, leading to the significant enhancement of heat transfer through the micro-convection and transient conduction mechanisms. Specifically, the heat transfer coefficient value of the nanostructured surface is more than 1.5 times that of the microstructured surface, thus achieving an increment of ∼5% in freshwater productivity.

A dataset of dual calcium and voltage optical mapping in healthy and hypertrophied murine hearts

Pathological hypertrophy underlies sudden cardiac death due to its high incidence of occurrence of ventricular arrhythmias. The alteration of transmural electrophysiological properties in hypertrophic cardiac murine tissue has never been explored previously. In this dataset, we have for the first time conducted high-throughput simultaneous optical imaging of transmembrane potential and calcium transients (CaT) throughout the entire hypertrophic murine hearts at high temporal and spatial resolution. Using ElectroMap, we have conducted multiple parameters analysis including action potential duration/calcium transient duration, conduction velocity, alternans and diastolic interval. Voltage-calcium latency was measured as time difference between action potential and CaT peak. The dataset therefore provides the first high spatial resolution transmural electrophysiological profiling of the murine heart, allowing interrogation of mechanisms driving ventricular arrhythmias associated with pathological hypertrophy. The dataset allows for further reuse and detailed analyses of geometrical, topological and functional analyses and reconstruction of 2-dimensional and 3-dimentional models.

Modelling of heat transfer within heterogeneous media by Brownian walkers

This work concerns the modelling of transient thermal conduction within a heterogeneous medium by the movement of Brownian walkers. The material structure is voxelised, and each walker transports an elementary enthalpy during its displacement within the structure. This enthalpy transport represents the conductive flow and makes it possible to simulate the conduction in a transient state with a quantitative stochastic approach. A study of the impact of the value of the time step is carried out to fix the choice conditions of this parameter, in particular in the presence of strong contrasts in thermophysical properties, and as such to define a validity framework of the diffusion model. Then several academic problems related to the behaviour of walkers are resolved in order to be able to account for different thermal solicitations and conditions at the boundaries (Dirichlet, Neumann, Newton) with Brownian walkers. These results have in particular made it possible to reproduce the so-called “rear face flash” experimental technique using a model by Brownian walkers over a homogeneous medium. Then, a stochastic transmission criterion based on the thermal effusivities is demonstrated to treat the meeting of a walker with an interface between two constituents within a heterogeneous medium. This work, focused on the mastery of the dynamics of Brownian walkers within heterogeneous media for the correct simulation of transient conduction, is a first step towards the modelling of the transient conduction-radiation coupling by means of Brownian walkers coupled to ray tracing techniques at the local scale of a voxelised structure.

Heat transfer behavior in ultrahigh-speed continuous casting mold

AbstractThe growth rate of the shell thickness in the funnel mold for ultrahigh-speed continuous casting of steel has a significant effect on the shell surface quality. By using the node temperature inheritance algorithm, a three-dimensional transient thermal conductivity model of the liquid steel solidification inside the mold was established, and the effects of casting temperature and speed on the heat transfer behavior of the thin slab were investigated. The results show that with an increase in the casting speed from 4.0 to 6.0 m·min−1, the maximum thickness of the shell at mold exit was reduced from 26 to 12.8 mm, and the maximum temperature of the slab surface at mold exit increased from 1,210 to 1,305°C. However, the increase of casting temperature from 1,550 to 1,560°C had little effect on the surface temperature and thickness of the slab shell.

Late-onset atrioventricular block after transcatheter aortic valve replacement.

BackgroundConduction disturbances leading to permanent pacemaker implantation (PPI) rarely occur late after transcatheter aortic valve replacement (TAVR). The clinical features of this phenomenon and its association with periprocedural conduction disturbances remain uncertain.ObjectivesWe aimed to determine the incidence and characteristics of late-onset atrioventricular block (AVB) after TAVR.MethodsThis single-center study included 246 patients undergoing TAVR. Late-onset AVB was defined as AVB ≥1 month after the TAVR.ResultsPeriprocedural AVB (periAVB) occurred in 43 patients (17%). Patients with periAVB had a higher rate of right bundle branch block (47% vs 7%, P < .0001). Of the 43 patients with periAVB, 15 underwent PPI (35%) at a median duration of 6 days, whereas 1 of the remaining 203 patients without periAVB underwent PPI within 1 month (0.5%). During a median follow-up duration of 365 days, late-onset AVB occurred in 10 of 230 patients without PPI within 1 month (4%) at a median duration of 76 days. All 10 patients presented transient periprocedural atrioventricular conduction disturbances, including 8 patients with periAVB (80%), all of whom recovered within 1 month, and 9 patients underwent self-expanding valve implantation (90%). The mortality rate in patients with PPI within 1 month was higher than in those without, although the difference was not statistically significant (hazard ratio 2.68, 95% confidence interval 0.97–9.05, log-rank P = .09).ConclusionLate-onset AVB occurred in a minority of patients undergoing TAVR. Greater vigilance is warranted, particularly in patients with transient conduction disturbances during the periprocedural period following self-expanding valve implantation.

Investigation of transient coupled conduction and radiation heat transfer in the linearly anisotropic scattering cylindrical medium by spectral collocation method

In this paper, a spectral collocation method (SCM) is developed to solve transient conduction and radiation heat transfer problems in infinitely long annular cylinders with participating medium. The participating medium is an absorbing, emitting and linearly anisotropic scattering medium. To avoid the complex calculation of ray tracing, the radiative transfer equation and the transient heat conduction equation are expressed in eulerian coordinates. In the solving process, for the radiative transfer equation, both spatial and angular domains are discretized by the SCM; for the transient heat conduction equation, the spatial domain is discretized by the SCM, and the time domain is discretized by the fully implicit Euler scheme. The spatial derivative term, angular derivative term and scattering source integral term are approximated by the high order spectral collocation scheme. Compared with available data in references, the SCM can achieve very good accuracy even using few nodes. Thus, the SCM is a very effective method to achieve high order accuracy for transient coupled conduction and radiation heat transfer in an anisotropic scattering cylindrical medium. Moreover, the effects of conduction-radiation parameter, optical thickness, and wall emissivity on the transient temperature distribution and energy flow rate have also been comprehensively investigated.

Preparation and Physicochemical Properties of Inorganic Two-dimensional Nanomaterial/Fullerene Composites

Atomically thin two-dimensional (2D) materials have attracted significant scientific interest because of their outstanding physicochemical properties. In contrast to semimetal graphene composed of carbon atoms, mono-elemental 2D materials exfoliated from layered crystals are semiconductors with finite electronic bandgaps, rendering them promising components for next-generation electronic and optoelectronic devices. Among them, nanosheets of black phosphorus (BP) with a puckered honeycomb structure have been predominantly explored due to its layer-controlled direct bandgap, from 0.3 eV in the bulk to 2.0 eV in monolayers. A high carrier mobility of BP exceeding 10000 cm2 V−1 s−1 also enhances its utility. However, BP is extremely sensitive to its environment and can be easily degraded by exposure to light, moisture, and oxygen, which severely limits its applications.Considering its outstanding stability under ambient conditions, molybdenum disulfide (MoS2), tungsten disulfide (WS2), and antimonene (Sb) are attractive alternatives that have a similar structure to that of BP. Theoretical and experimental studies have revealed their various remarkable physicochemical properties, such as tunable bandgap and high electrical conductivity.In this talk I will give an overview of our recent studies on two-dimensional nanomaterial/fullerene composites. In particular, the composites on SnO2 exhibited enhanced transient conductivity relative to single components, which demonstrates that the composites promoted the photoinduced charge separation.[1] J. Baek, T. Umeyama, W. Choi, Y. Tsutsui, H. Yamada, S. Seki, and H. Imahori, Chem. Eur. J., 24, 1561-1572 (2018).[2] T. Umeyama, T. Ohara, Y. Tsutsui, S. Nakano, S. Seki, and H. Imahori, Chem. Eur. J., 26, 6726-6735 (2020).

Multiscale analysis of thermal problems in heterogeneous materials with Direct FE2 method

AbstractMultiscale thermal analysis is motivated by efficient modeling of complex microstructural response (nonlinear conduction, transient conduction, coupled thermomechanics, etc.) without resorting to fully resolved simulations, direct numerical simulation (DNS). It is typically conducted with an FE method that couples two levels of finite element simulations in a nested manner. This article presents a Direct FE method for modeling heat transfer problems in heterogeneous solids. The proposed method is developed based on the same theoretical framework as the FE method, namely downscaling and upscaling rules. However, the scale transitions are achieved through temperature/nodal thermal force in Direct FE rather than temperature gradient/heat flux in common FE implementations. The two‐level simulations can be solved in a monolithic scheme where the macroscopic and microscopic DOFs are coupled through multi‐point constraints. This feature allows an easy implementation in standard FE packages without resorting to repeated transfer of data between two scales. For transient thermal problems, the implementation provides an option to either incorporate or exclude thermal inertial effects and heat generation at the microscale. The performance of the Direct FE is demonstrated by several numerical examples including coupled thermal‐mechanical analysis and transient heat conduction, and the results are compared with DNSs.

Prevention of Frost Heave in the Surrounding Rocks of Tunnel for Ski Resorts

Taking the four-season ski resort in Jilin Beishan as an example, this paper analyses the temperature field of surrounding rocks by applying the theory of transient thermal conductivity of semi-infinite large objects, and explains the necessity of insulation isolation layer and heating system setting. The structure and insulation performance of the insulation isolation layer are specified, and the flat wall steady-state thermal conductivity theory is used to calculate that the heat transfer on both sides of the insulation layer is about 29.66kW. This heat is not only a part of the cooling load of the snow resort refrigeration system, but also a part of the heat load of the wall heating system. For the refrigeration system, the COP value of the chiller is 2.5kW/kW. Even excluding the energy consumption of the transmission and distribution process, the annual power consumption of the cooling load alone is about 104,000 KWH, which explains the importance of the temperature control system and insulation layer. The heat source of the heating system of this project innovatively adopts the waste heat of cooling generated in the refrigeration process. This measure makes the heating source of this project no longer consume fossil energy, resulting in significant energy saving and emission reduction benefits. As described, a tunnel ski resort similar to a new or rebuild one can be used as a reference. Some of the results can be applied to prevention of frost heave of traffic tunnels in high-cold and high-latitude areas.

Deducing flux from single point temperature history when relative spatial variation of flux is prescribed

Surface heat transfer in convective and radiative environments is sometimes measured by recording the surface temperature history in a transient experiment and interpreting this surface temperature with the aid of a suitable model for transient conduction within the substrate. The semi-infinite one-dimensional model is often adopted, and several well-developed techniques for application of this model to surface temperature data are available. However, when a spatial variation of heat flux exists across the surface, the application of the semi-infinite one-dimensional approach may not always be a reasonable approximation because the errors are transient and typically increase with time. In this paper we introduce a method for treatment of the measured surface temperature history that is more accurate than the semi-infinite one-dimensional approximation when substrate lateral conduction is significant and the relative spatial distribution of the flux is known a priori. This new method uses the so-called Neumann heat kernel, which evolves a temperature over an insulated domain with unit energy initially deposited at a specified point. A useful impulse response function is formed by integrating this Neumann heat kernel against the spatial variation of flux over the surface of the domain. By applying the heat kernel result for the sphere to the analysis of a convective experiment using hemispherical-nosed probes, we demonstrate how the theoretical results enhance the practical analysis of transient surface temperature measurements. The current approach is superior to former methods relying on semi-empirical approximations because the multi-dimensional heat conduction within the substrate is modelled with greater fidelity using the heat kernel analysis.

RETRACTED ARTICLE: Nanoparticle effect of heat conduction mechanism during solidification of PCM

In this modeling investigation, freezing of NEPCM inside a chamber with triangular cold cylinder has been scrutinized. With mixing copper oxide nano-powders and H2O, new material has been generated. To include the impact of nano-powder shape, empirical correlations were utilized. For simulation of such transient conduction mechanism, finite element approach was applied with considering grid adaption. Amplitude of top wall and shape coefficient were two active factors and simulations were demonstrated their effects. Examination of accuracy of code shows nice agreement. Adding nano-powders enhances the conduction and style of powders can affect the freezing process. The minimum time for full freezing is 197.0352 s which can be achieved when A = 0.3 and m = 5.7. Augment of shape factor leads to decrement of time by 8.36%. With rise of A, freezing time declines by 11.78% because PCM volume decreases inside the chamber.

Acute coronary syndrome with ST-segment elevation caused by in-stent thrombosis in the setting of COVID-19 infection

We present a case of a 75-year-old male who underwent percutaneous coronary intervention in the setting of acute myocardial infarction with ST-segment elevation and who was hospitalized 12 days afterwards with COVID-19 pneumonia. Later the patient presented himself again with acute coronary syndrome with ST-segment elevation in the same region due to in-stent thrombosis. Transient atrioventricular conduction disorders were registered before and after the percutaneous coronary intervention. Possible pathophysiological mechanisms of the in-stent thrombosis following COVID-19 infection are discussed.

Impact of Persistent vs. Transient Conduction Abnormalities Within 7 Days Post-TAVR on Mortality: Results of a Single-Center Prospective Registry

Impact of Persistent vs. Transient Conduction Abnormalities Within 7 Days Post-TAVR on Mortality: Results of a Single-Center Prospective Registry

Spectroscopic view of ultrafast charge carrier dynamics in single- and bilayer transition metal dichalcogenide semiconductors

The quasiparticle spectra of atomically thin semiconducting transition metal dichalcogenides (TMDCs) and their response to an ultrafast optical excitation critically depend on interactions with the underlying substrate. Here, we present a comparative time- and angle-resolved photoemission spectroscopy (TR-ARPES) study of the transient electronic structure and ultrafast carrier dynamics in the single- and bilayer TMDCs MoS2 and WS2 on three different substrates: Au(111), Ag(111) and graphene/SiC. The photoexcited quasiparticle bandgaps are observed to vary over the range of 1.9–2.5 eV between our systems. The transient conduction band signals decay on a sub-50 fs timescale on the metals, signifying an efficient removal of photoinduced carriers into the bulk metallic states. On graphene, we instead observe a fast timescale on the order of 170 fs, followed by a slow dynamics for the conduction band decay in MoS2. These timescales are explained by Auger recombination involving MoS2 and in-gap defect states. In bilayer TMDCs on metals we observe a complex redistribution of excited holes along the valence band that is substantially affected by interactions with the continuum of bulk metallic states.