Thermal Plateau Research Articles

Systemic microvascular endothelial dysfunction and disease severity in COVID-19 patients: Evaluation by laser Doppler perfusion monitoring and cytokine/chemokine analysis

BackgroundMicrovascular dysfunction, serum cytokines and chemokines may play important roles in pathophysiology of coronavirus disease 2019 (COVID-19), especially in severe cases. MethodsPatients with COVID-19 underwent non-invasive evaluation of systemic endothelium-dependent microvascular reactivity - using laser Doppler perfusion monitoring in the skin of the forearm - coupled to local thermal hyperemia. Maximal microvascular vasodilatation (44 °C thermal plateau phase) was used as endpoint. A multiplex biometric immunoassay was used to assess a panel of 48 serum cytokines and chemokines. Severe COVID-19 (S-COVID) was defined according to WHO criteria, while all other cases of COVID-19 were considered mild to moderate (M-COVID). A group of healthy individuals who tested negative for SARS-CoV-2 served as a control group and was also evaluated with LDPM. ResultsThirty-two patients with COVID-19 (25% S-COVID) and 14 controls were included. Basal microvascular flow was similar between M-COVID and controls (P = 0.69) but was higher in S-COVID than in controls (P = 0.005) and M-COVID patients (P = 0.01). The peak microvascular vasodilator response was markedly decreased in both patient groups (M-COVID, P = 0.001; S-COVID, P < 0.0001) compared to the healthy group. The percent increases in microvascular flow were markedly reduced in both patient groups (M-COVID, P < 0.0001; S-COVID, P < 0.0001) compared to controls. Patients with S-COVID had markedly higher concentrations of dissimilar proinflammatory cytokines and chemokines, compared to patients with M-COVID. ConclusionsIn patients with COVID-19, especially with S-COVID, endothelium-dependent microvascular vasodilator responses are reduced, while serum cytokines and chemokines involved in the regulation of vascular function and inflammation are increased.

Hyper-cooling limit, heat of fusion, and temperature-dependent specific heat of Fe-Cr-Ni melts

Thermophysical properties of Fe-Cr-Ni melts are studied using electrostatic levitation and rapid solidification techniques. Six hypoeutectic Fe0.72CrwNi(0.28−w) alloys with a Cr/Ni ratio of around 0.8 were melted and solidified at different degrees of undercooling. From the observed relationship between the undercooling and thermal plateau time, the hyper-cooling limit and heat of fusion of Fe0.72CrwNi(0.28−w) melts are determined as a function of Cr mass fraction. A ratio of specific heat and total hemispherical emissivity of the Fe-Cr-Ni melts is calculated using the time-temperature profiles. A new method is presented to evaluate the temperature dependence of specific heat for undercooled melts and applied to this alloy family.

Global quantum discord and thermal tensor network in XXZ chains at finite temperatures

We characterize multi-site quantum correlations in 1D finite-size XXZ chains at finite temperatures with global quantum discord. With the help of an exact diagonalization method and a thermal-tensor-network algorithm, the thermal-state discord G(ρˆT) is evaluated efficiently by well-developed optimization algorithms. Firstly, we find that in a finite temperature region, G(ρˆT) shows some footprint of the quantum phase transition of the model. The underlying mechanism is that ρˆT captures the level crossing in the low-lying excited states. Secondly, we study the temperature dependence of G(ρˆT). When the anisotropy is strong, G(ρˆT) will show a broad thermal plateau. We offer a quantitative explanation of the plateau by truncating the thermal-state operator ρˆT with respect to several low-lying states. Thirdly, we investigate the scaling behavior of G(ρˆT). We find that when N is large enough, G(ρˆT) would show a linear scaling. Finally, combined with the thermal tensor networks and the linear scaling behavior, we successfully figure out reliable results for G(ρˆT) in the full-temperature regions with N up to 16. We believe that the thermal tensor networks will play a role in studying general multi-site quantum correlations in 1D chains at finite temperatures.

Influence of the addition of hydrocolloids on the thermal, pasting and structural properties of starch from common vetch seeds (Vicia sativa sp)

Belonging to the leguminous family, the common vetch seeds are a non-conventional starch source that can be exploited to attend the growing demand of the food industry. Thus, the aim of this study was to evaluate the influence of addition of hydrocolloids (5% of: carrageenan, carboxymethylcellulose (CMC), guar, jatahy, xanthan and pectin) on the thermal, pasting and structural properties of starch from common vetch (Vicia sativa) seeds. The interaction with the hydrocolloids was analysed by thermogravimetry and derivative thermogravimetry, differential scanning calorimetry (DSC), viscoamylographic analysis (RVA) and X-ray powder diffraction (DRX). From the thermogravimetry, a similar behaviour was observed for all the studied samples, with three well-defined mass losses and a thermal stability plateau. The addition of guar gum promoted an increase in its thermal stability, unlike the sample added of CMC. From the DSC analysis, it was possible to observe a decrease in onset temperatures with the addition of hydrocolloids, which can be correlated with the decrease in pasting temperatures obtained by RVA, except for the carrageenan gum, which increased these temperatures. By RVA an increase in peak viscosities was achieved, highlighting the addition of CMC, pectin and xanthan. Small variations in the degree of relative crystallinity were noted, but no changes in the diffraction pattern occurred for the samples from the XRD analysis. Although native starch has some limitations, the synergistic effect produced by the addition of gums can optimise its technological properties expanding the industrial use.

Mass ejection in failed supernovae: variation with stellar progenitor

We study the ejection of mass during stellar core-collapse when the stalled shock does not revive and a black hole forms. Neutrino emission during the protoneutron star phase causes a decrease in the gravitational mass of the core, resulting in an outward going sound pulse that steepens into a shock as it travels out through the star. We explore the properties of this mass ejection mechanism over a range of stellar progenitors using spherically-symmetric, time-dependent hydrodynamic simulations that treat neutrino mass loss parametrically and follow the shock propagation over the entire star. We find that all types of stellar progenitor can eject mass through this mechanism. The ejected mass is a decreasing function of the surface gravity of the star, ranging from several $M_\odot$ for red supergiants to $\sim 0.1M_\odot$ for blue supergiants and $\sim 10^{-3} M_\odot $ for Wolf-Rayet stars. We find that the final shock energy at the surface is a decreasing function of the core-compactness, and is $\lesssim 10^{47}-10^{48}$ erg in all cases. In progenitors with a sufficiently large envelope, high core-compactness, or a combination of both, the sound pulse fails to unbind mass. Successful mass ejection is accompanied by significant fallback accretion that can last from hours to years. We predict the properties of shock breakout and thermal plateau emission produced by the ejection of the outer envelope of blue supergiant and Wolf-Rayet progenitors in otherwise failed supernovae.

High Electric Field Carrier Transport and Power Dissipation in Multilayer Black Phosphorus Field Effect Transistor with Dielectric Engineering

This study addresses high electric field transport in multilayer black phosphorus (BP) field effect transistors with self‐heating and thermal spreading by dielectric engineering. Interestingly, a multilayer BP device on a SiO2 substrate exhibits a maximum current density of 3.3 × 1010 A m−2 at an electric field of 5.58 MV m−1, several times higher than multilayer MoS2. The breakdown thermometry analysis reveals that self‐heating is impeded along the BP–dielectric interface, resulting in a thermal plateau inside the channel and eventual Joule breakdown. Using a size‐dependent electro‐thermal transport model, an interfacial thermal conductance of 1–10 MW m−2 K−1 is extracted for the BP–dielectric interfaces. By using hexagonal boron nitride (hBN) as a dielectric material for BP instead of thermally resistive SiO2 (κ ≈ 1.4 W m−1 K−1), a threefold increase in breakdown power density and a relatively higher electric field endurance is obtained together with efficient and homogenous thermal spreading because hBN has superior structural and thermal compatibility with BP. The authors further confirm the results based on micro‐Raman spectroscopy and atomic force microscopy, and observe that BP devices on hBN exhibit centrally localized hotspots with a breakdown temperature of 600 K, while the BP devices on SiO2 exhibit hotspots in the vicinity of the electrode at 520 K.

Peculiarities in the transport characteristics of phonons in glasses and glass-like crystals at helium temperatures

Peculiarities in the transport characteristics of thermal-frequency phonons are analyzed in the region of transition to the thermal conductivity plateau in fused quartz, F-1 glass, glassed based on pentaphosphates of rare-earth metals, and a number of ferroelectrics (relaxors). It is shown that the formation of the plateau region in the temperature dependence of thermal conductivity at T < 10 K for these materials can be associated with the occurrence of a gap in the spectrum of phonon states.

Diffusion and Fokker-Planck-Smoluchowski Equations with Generalized Memory Kernel

Abstract We consider anomalous stochastic processes based on the renewal continuous time random walk model with different forms for the probability density of waiting times between individual jumps. In the corresponding continuum limit we derive the generalized diffusion and Fokker-Planck- Smoluchowski equations with the corresponding memory kernels. We calculate the qth order moments in the unbiased and biased cases, and demonstrate that the generalized Einstein relation for the considered dynamics remains valid. The relaxation of modes in the case of an external harmonic potential and the convergence of the mean squared displacement to the thermal plateau are analyzed.

Signatures of energy flux in particle production: a black hole birth cry and death gasp

It is recently argued that if the Hawking radiation process is unitary, then a black hole's mass cannot be monotonically decreasing. We examine the time dependent particle count and negative energy flux in the non-trivial conformal vacuum via the moving mirror approach. A new, exactly unitary solution is presented which emits a characteristic above-thermal positive energy burst, a thermal plateau, and negative energy flux. It is found that the characteristic positive energy flare and thermal plateau is observed in the particle outflow. However, the results of time dependent particle production show no overt indication of negative energy flux. Therefore, a black hole's birth cry is detectable by asymptotic observers via particle count, whereas its death gasp is not.

Anomalous diffusion and power-law relaxation of the time averaged mean squared displacement in worm-like micellar solutions

We report the results of single tracer particle tracking by optical tweezers and video microscopy in micellar solutions. From careful analysis in terms of different stochastic models, we show that the polystyrene tracer beads of size 0.52–2.5 μm after short-time normal diffusion turn over to perform anomalous diffusion of the form 〈r2(t)〉 ≃ tα with α ≈ 0.3. This free anomalous diffusion is ergodic and consistent with a description in terms of the generalized Langevin equation with a power-law memory kernel. With optical tweezers tracking, we unveil a power-law relaxation over several decades in time to the thermal plateau value under the confinement of the harmonic tweezer potential, as predicted previously (Phys. Rev. E 85 021147 (2012)). After the subdiffusive motion in the millisecond range, the motion becomes faster and turns either back to normal Brownian diffusion or to even faster superdiffusion, depending on the size of the tracer beads.

Hatchling Crocodiles Maintain a Plateau of Thermal Independence for Activity, but at What Cost?

Abstract Crocodilians show a broad plateau of thermal independence for sustained activity. It has been hypothesized that this reflects a performance breadth necessary for carrying out ecologically important behaviors across a range of ambient temperatures. Here, we swam Saltwater Crocodiles (Crocodylus porosus) in a thermally controlled flume at 23, 28, and 33°C and recorded oxygen consumption (VO2) before and after swimming activity. Ambient temperature altered spontaneous VO2 in a positively linear manner, but there was no significant difference in the distance the crocodiles would swim voluntarily. Excess postexercise oxygen consumption (EPOC) increased 10-fold between swimming trials at 28 and 33°C, and the anaerobic debt took 3 times longer to clear at the higher temperature. The results show that, although C. porosus demonstrated a broad thermal breadth for swimming performance, a higher degree of anaerobic metabolism was required to sustain activity at the upper limits of the thermal plateau. Why c...

Assessment of Skin Microvascular Function and Dysfunction With Laser Speckle Contrast Imaging

In recent years, skin microcirculation has been considered an easily accessible and potentially representative vascular bed to evaluate and understand the mechanisms of microvascular function and dysfunction.1–3 Vascular dysfunction (including impaired endothelium-dependent vasodilation) induced by different pathologies is evident in the cutaneous circulation.4–7 It has been suggested that the skin microcirculation may mirror generalized systemic vascular dysfunction in magnitude and underlying mechanisms.1 Furthermore, minimally invasive skin-specific methodologies using laser systems make the cutaneous circulation a useful translational model for investigating mechanisms of skin physiology and skin pathophysiology induced either by skin disease itself or by other diseases such as vascular, rheumatologic, and pneumologic. To date, the skin has been used as a circulation model to investigate vascular mechanisms in a variety of diseased states, including hypercholesterolemia,8 Alzheimer disease,9 carpal tunnel syndrome,10 schizophrenia,11 hypertension,6 renal disease,12 type 2 diabetes,13 peripheral vascular disease,14 atherosclerotic coronary artery disease,2 heart failure,15 systemic sclerosis,16 obesity,17 primary aging,18,19 and sleep apnea.20 Assessment of skin microvascular function can be done by both invasive and noninvasive techniques. Among noninvasive techniques, laser systems are mainly used.21 The recent development of the laser speckle contrast imaging (LSCI) technique for monitoring skin microvascular function enables its use as a surrogate end point in clinical trials. LSCI allows for noncontact, real-time, and noninvasive monitoring of cutaneous blood flow changes.22,23 Recent evidence has shown that the LSCI technique dramatically reduces the variability of clinical measurements compared with laser Doppler flowmetry (LDF), making the technique a fascinating tool to facilitate microvascular studies in clinical routine.23,24 In this review, we describe …

Application of dendrite fragmentation to fabricate the homogeneous dispersed structure in undercooled Cu–Co immiscible alloy

The dependence of microstructure on undercooling for Cu 50Co 50 immiscible alloy and the relations between dendrite fragmentation and liquid phase separation were studied by melt-fluxing in combination with cyclic superheating. It is shown that homogeneous dispersed structure can be obtained by dendrite fragmentation because of the increased solute content in primary dendrite, which is advantageous for strengthening dendrite remelting effect and thermal plateau time following recalescence. As for the sample after liquid separation, typical dual-layer structure forms, while dendrite fragmentation still exists and its extent, volume fraction are influenced by the solute contents of two immiscible layers. Quantitative thermodynamic calculation was further performed to support the experimental results.

Local Heating as a Predilatation Method for Measurement of Vasoconstrictor Responses with Laser‐Doppler Flowmetry

Studying microvascular responses to iontophoresis of vasoconstricting drugs contributes to a better understanding of the regulatory mechanisms of cutaneous vessels, but measuring these responses with laser-Doppler flowmetry at basal blood flow conditions is technically challenging. This study aimed to investigate whether the measurement of cutaneous vasoconstrictor responses to noradrenaline (NA) and phenylephrine (PE), delivered by iontophoresis, is facilitated by predilatation of the microvascular bed using local heating. We used different drug delivery rates (100 s × 0.12 mA, 200 s × 0.06 mA, 300 s × 0.04 mA) to investigate whether predilatation affects the local drug dynamics by an increased removal of drugs from the skin. In a predilatated vascular bed, iontophoresis of NA and PE resulted in a significant decrease in perfusion from the thermal plateau (p < 0.001). The decrease was 25-33%, depending on drug delivery rate. In unheated skin, a significant vasoconstriction was observed (p < 0.001), with 17% and 14% decrease from baseline for NA and PE, respectively. These results indicate that predilatating the cutaneous vascular bed by local heating facilitates measurement of vasoconstriction with laser-Doppler flowmetry and does not seem to significantly affect the result by an increased removal of drugs from the skin.

Study of oxygen clustering in Czochralski silicon at 450 °C–800 °C: correlation with thermal donors formation

AbstractThe understanding of the generation‐annihilation phenomena of oxygen‐related thermal donors (TDs) in p‐type Czochralski silicon is of great importance for device fabrication and operation in microelectronic and photovoltaic industry. In this work, we report on oxygen clustering‐based activation and partial annihilation of TDs in Cz‐Si submitted to thermal annealing under nitrogen at 450 °C‐800 °C for different thermal plateau exceeding 4 hours. The effect of thermal annealing on interstitial oxygen and dimer (Oi and O2i) vibration modes appearing in the 580 cm‐1‐500 cm‐1 spectral range is studied. We found that heat treatment at 450°C and 650 °C give rise to new thermal donors (NDs) that are located at 540 cm‐1 and 532 cm‐1, respectively. Subsequent to heat treatment above 650 °C, we depict the formation of new thermal oxygen defects having an IR signature in the 1800 cm‐1‐1500 cm‐1 spectral range, and which are especially sensitive to the thermal treatment duration. Resistivity measurements confirm that several of them are electrically active. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Use of recalescence behavior analysis for the prediction of grain refinement in undercooled Cu–Ni alloy

Considering non-equilibrium solidification and its influence on subsequent near-equilibrium solidification together, the description of recalescence behavior in bulk undercooled Cu70Ni30 alloy was adopted to predict the corresponding microstructure transition. The thermal plateau time for near-equilibrium solidification can be deduced directly with the calculation of non-equilibrium solid fraction formed in recalescence. On the basis of quantitative description for recalescence behavior, the non-equilibrium solid fraction, residual liquid fraction, dendrite broken-up time, and thermal plateau time can be determined as functions of initial undercooling. Then, a simple and accurate application of dendrite fragmentation model was performed as the grain refinement at both low- and high-undercooling originates from dendrite breakup. The predicted undercooling regions for the double grain refinement agree well with the experimental observation. Moreover, the change of grain morphology for the second grain refinement can be ascribed to the occurrence of recrystallization produced by the enhanced residual stress upon highly undercooled solidification.

Excellent reproducibility of laser speckle contrast imaging to assess skin microvascular reactivity

Objective We compared the inter-day reproducibility of post-occlusive reactive hyperemia (PORH) assessed by single-point laser Doppler flowmetry (LDF) and laser speckle contrast analysis (LSCI), and the reproducibility of local thermal hyperemia (LTH) assessed by LDF, laser Doppler imaging (LDI) and LSCI. We also tested whether skin blood flow assessment by LDF and by LSCI are correlated. Methods Skin blood flow was evaluated during PORH and LTH using LDF, LDI (for LTH only) and LSCI on the forearms of healthy volunteers, at a 7 day interval. Data are expressed as cutaneous vascular conductance (CVC), as a function of baseline and scaled to the thermal plateau. Reproducibility is expressed as within subject coefficients of variation (CV, in %) and intra-class correlation coefficients (ICC). Results Twenty-eight healthy participants were enrolled in this study. The reproducibility of the PORH peak CVC was better when assessed with LSCI compared to LDF (CV = 8%; ICC = 0.76 and CV = 30%; ICC = 0.54, respectively). Inter-day reproducibility of the LTH plateau was better when assessed with LSCI or LDI than LDF (CV = 15%, ICC = 0.66; CV = 17%, ICC = 0.51 and CV = 42%, ICC = 0.28 respectively). Finally, we observed significant correlation between simultaneous LDF and LSCI measurements of the PORH peak CVC (R = 0.54; p = 0.001). Conclusion The recently developed LSCI technique showed very good inter-day reproducibility for assessing PORH and LTH. Moreover, we showed significant correlation between LSCI and single-point LDF for PORH. However, more data are needed to evaluate the linearity between the LSCI signal and skin blood flow.

THERMAL TRANSPORT BY BALLISTIC PHONON IN A SEMICONDUCTOR RECTANGULAR QUANTUM WIRE MODULATED WITH QUANTUM DOT

Thermal transport by ballistic phonon in a semiconductor rectangular quantum wire modulated with quantum dot at low temperatures is investigated with the use of the scattering matrix method. The calculated results show that the total transmission coefficient versus the reduced phonon frequency exhibits interesting characteristics such as inhomogeneous quantum transport steps. Quantized thermal conductance plateau can be observed at low temperatures, and the thermal conductance is not increased monotonically with increasing temperature. The results also show that the phonon transport probability and thermal conductance can be controlled to a certain degree by adjusting the parameters of the proposed quantum structure.

Acoustic phonons transport in a quantum waveguide embedded double defects

By using scattering matrix method, we investigate the acoustic phonons transport in a quantum waveguide embedded double defects at low temperatures. When acoustic phonons propagate through the waveguide, the total transmission coefficient versus the reduced phonon frequency exhibits a series of resonant peaks and dips, and acoustic waves interfere with each other in the waveguide to form standing wave with particular wavelengths. In the waveguide with void defects, acoustic phonons whose frequencies approach zero can transport without scattering. The acoustic phonons propagating in the waveguide with clamped material defects, the phonons frequencies must be larger than a threshold frequency. It is also found that the thermal conductance versus temperature is qualitatively different for different types of defects. At low temperatures, when the double defects are void, the universal quantum thermal conductance and a thermal conductance plateau can be clearly observed. However, when the double defects consist of clamped material, the quantized thermal conductance disappears but a threshold temperature where mode 0 can be excited emerges. The results can provide some references in controlling thermal conductance artificially and the design of phonon devices.

The Thermal Circulation of a Grand Plateau: Sensitivity to the Height, Width, and Shape of the Plateau

Abstract Idealized numerical simulations are presented to investigate the sensitivity of the thermal plateau circulation to the plateau height, width, and the presence of a mountain ridge encompassing the plateau. The study concentrates on plateaus surrounded by land with the same surface properties so that the topography is the only source of differential heating. For low plateaus, it is found that the strength of the plateau circulation increases with the plateau height because the excess heating of the plateau increases with its height. The plateau circulation reaches its maximum strength for plateau heights similar to the mixed-layer depth over the surrounding lowlands. For even higher plateaus, the depth of the circulation decreases whereas the peak intensity exhibits little change. The plateau height also controls the temporal evolution of the plateau circulation. For low plateaus, low-level inflow is primarily found during the night because convection cells forming over the lateral slopes prevent an inward mass flux during the day. With increasing plateau height, the phases of the plateau circulation shift toward earlier times. If the plateau height exceeds the mixed-layer depth over the surrounding lowlands, inflow occurs from afternoon until the late evening. After sunset, the inflow layer tends to assume the characteristics of a density current. The convergence of the density currents propagating from each side of the plateau toward the center helps to fill the heat low formed during the day. Moreover gravity waves are triggered that propagate away from the plateau center and terminate the inflow. The propagation speed of the density currents is found to increase with the plateau height, so that their convergence occurs earlier for high plateaus than for low plateaus. For the parameter range considered in this study, the plateau width is found to have only a minor impact on the mass fluxes associated with the plateau circulation. However, the convergence of the density currents over the plateau center occurs later for a wider plateau, implying that the heat low is more persistent. Substantial changes are obtained when the plateau is surrounded by a mountain ridge. In this case, the inflow toward the plateau gets delayed because a slope wind circulation forms over the mountain ridge. Moreover, the mass fluxes toward the plateau are reduced so that the heat low that formed over the plateau during the day is filled only slowly. As a consequence, the inflow lasts throughout the night in the presence of a high mountain ridge surrounding the plateau.