Temperature Jump Research Articles

Electrostatic turbulence in electron temperature jumps of the solar atmosphere

We discuss the connection of the formation and properties of solar atmosphere transition region characterized by a steep electron temperature gradient with electrostatic turbulence, which provides a high effective electron collision frequency and a low thermal conductivity of the medium. A simple dependence of the noise electric field in the transition region on the effective collision frequency has been derived. Based on known experimental models of the solar atmosphere, we have estimated the height dependence of the thermal conductivity and the strength of the noise electric fields for a tube with a relatively weak magnetic field passing from the chromosphere into the corona.

X-ray cavities and temperature jumps in the environment of the strong cool core cluster Abell 2390

We present results based on the systematic analysis of high resolution 95 ks Chandra observations of the strong cool core cluster Abell 2390 at the redshift of z= 0.228 that hosts an energetic radio AGN. This analysis has enabled us to investigate five X-ray deficient cavities in the atmosphere of Abell 2390 within central 30". Presence of these cavities have been confirmed through a variety of image processing techniques like, the surface brightness profiles, unsharp masked image, as well as 2D elliptical model subtracted residual map. Temperature profile as well as 2D temperature map revealed structures in the distribution of ICM, in the sense that ICM in the NW direction is cooler than that on the SE direction. Temperature jump in all directions is evident near 25" (90.5 kpc) corresponding to the average Mach number 1.44$\pm$0.05, while another jump from 7.47 keV to 9.10 keV at 68" (246 kpc) in the north-west direction, corresponding to Mach number 1.22$\pm$0.06 and these jumps are associated with the cold fronts. Tricolour map as well as hardness ratio map detects cool gas clumps in the central 30 kpc region of temperature $4.45_{-0.10}^{+0.16}$ keV. The entropy profile derived from the X-ray analysis is found to fall systematically inward in a power-law fashion and exhibits a floor near 12.20$\pm$2.54 keV cm$^2$ in the central region. This flattening of the entropy profile in the core region confirms the intermittent heating at the centre by AGN. The diffuse radio emission map at 1.4\,GHz using VLA L-band data exhibits highly asymmetric morphology with an edge in the north-west direction coinciding with the X-ray edge seen in the unsharp mask image.

弹道扩散导热的热质模型

The classical Fourier heat conduction law only works well for diffusive transport under normal conditions. Several typical non-Fourier models, such as the Cattaneo-Vernotte, dual-phase-lagging, and thermomass models, have been developed for thermal wave transport under transient conditions in recent decades. In addition, some recent studies have shown that the thermal conductivity of lowdimensional systems increases with increasing characteristic length because heat is transported in a ballistic-diffusive manner in nanostructures, in which the phonon mean free path (MFP) is comparable to the characteristic length. However, few models have become available for such thermal transport processes to date. In this work, we show that the general heat conduction law can be extended to phonon ballistic-diffusive transport by modification of the boundary conditions. First, we analyze the diffusive and ballistic transport processes from a thermomass theory viewpoint. Diffusive transport is transport in which thermal mass drifts in a body with a resistance proportional to the drift velocity, similar to fluid flows in porous media, and the current general heat conduction law can be derived from the thermomass balance equations, in which the heat inertia is considered. However, when the MFP is comparable with the characteristic length, the rarefied effect of the thermomass occurs, which corresponds to ballistic heat transport. In this regime, temperature jumps occur at the boundaries. It is noted here that the effects of ballistic heat transport are not covered in the current general heat conduction law. Therefore, modified boundary conditions that consider ballistic transport are applied to extend the general heat conduction law. We derive these modified boundary conditions from the phonon Boltzmann transport equation. The phonon distribution function is expanded with respect to the Knudsen number ( Kn ), and the continuous heat flux condition is used to obtain the modified boundary conditions. In addition, heat conduction in silicon nanofilms at room temperature is studied numerically, and comparisons with Monte Carlo simulations are also conducted to confirm the proposed theoretical models. It is found that our model can predict the temperature distributions well within silicon nanofilms with different Knudsen numbers. The size-dependent thermal conductivity can also be obtained using our model.

Lattice Boltzmann method for conjugate heat and mass transfer with interfacial jump conditions

In this work we propose an interface treatment for conjugate heat and mass transfer with discontinuities or jumps of temperature (concentration) and/or heat (mass) flux at the interface using the lattice Boltzmann equation (LBE) method. The present interface treatment is based on the second-order accurate boundary condition treatments for Dirichlet and Neumann problems (Li et al., 2013) and second-order accurate interface treatment for standard conjugate heat and mass transfer with the continuity of temperature (concentration) and flux at the interface (Li et al., 2014). The interfacial jump conditions are intrinsically satisfied in the present treatment without iterative computations that are typically needed in conventional finite-difference or finite-volume methods. The interfacial temperature (concentration) values and the fluxes into the adjacent domains are conveniently obtained from the microscopic distribution functions in the LBE model without finite-difference approximations. Since the local intersection link fraction is included in the present treatment, the interfacial geometry is preserved and the present interface schemes are capable of handling curved interfaces. The numerical accuracy and convergence of the present interface schemes are verified with several numerical tests, including (i) one-dimensional (1D) steady diffusion within a two-solid slab; the slab is either aligned with the lattice velocity vector or with an inclination angle, (ii) 2D steady diffusion in a circular domain of two concentric solids, (iii) 3D steady diffusion in a spherical domain of two concentric solids, and (iv) 2D steady convection–diffusion in a channel. The two adjacent domains have different thermal (mass) transport properties and specific temperature (concentration) and flux jump conditions are imposed at the interface in each of those tests. It is verified that the present interface treatment for jump conditions does not introduce additional errors compared to the case without jumps; and second-order accuracy in space is obtained for the interior temperature (concentration) field, the interfacial temperature (concentration) values and interfacial fluxes for straight interfaces aligned with the lattice velocity vector in both diffusion and convection–diffusion problems. The effects of inclined and curved interfacial geometry on the order-of-accuracy of the LBE results are also investigated and the results are compared with previous findings.

Flow and Heat Transfer of Nanofluids Over a Rotating Porous Disk with Velocity Slip and Temperature Jump

Abstract In this article, we discuss the flow and heat transfer of nanofluids over a rotating porous disk with velocity slip and temperature jump. Three types of nanoparticles – Cu, Al2O3, and CuO – are considered with water as the base fluid. The nonlinear governing equations are reduced into ordinary differential equations by Von Karman transformations and solved using homotopy analysis method (HAM), which is verified in good agreement with numerical ones. The effects of involved parameters such as porous parameter, velocity slip, temperature jump, as well as the types of nanofluids on velocity and temperature fields are presented graphically and analysed.

Steady-state heat transport: Ballistic-to-diffusive with Fourier's law

It is generally understood that Fourier's law does not describe ballistic phonon transport, which is important when the length of a material is similar to the phonon mean-free-path. Using an approach adapted from electron transport, we demonstrate that Fourier's law and the heat equation do capture ballistic effects, including temperature jumps at ideal contacts, and are thus applicable on all length scales. Local thermal equilibrium is not assumed, because allowing the phonon distribution to be out-of-equilibrium is important for ballistic and quasi-ballistic transport. The key to including the non-equilibrium nature of the phonon population is to apply the proper boundary conditions to the heat equation. Simple analytical solutions are derived, showing that (i) the magnitude of the temperature jumps is simply related to the material properties and (ii) the observation of reduced apparent thermal conductivity physically stems from a reduction in the temperature gradient and not from a reduction in actual thermal conductivity. We demonstrate how our approach, equivalent to Fourier's law, easily reproduces results of the Boltzmann transport equation, in all transport regimes, even when using a full phonon dispersion and mean-free-path distribution.

B214 強制流動サブクール沸騰DNBにおける伝熱面温度変化の予測(OS-01:沸騰・凝縮伝熱および混相流の最近の進展(3))

This paper gives prediction to the transient heat transfer at Departure of Nucleate Boiling (DNB) point for subcooled flow boiling. The prediction is carried out by solving the heat conduction equations in cylindrical coordinates with convective boundary condition, which changes with the change of the heat transfer mode on the heated surface. DNB is assumed to happen at the complete dryout of liquid sublayer trapped between the heated wall and an elongated vapor clot, during the passing time of the vapor clot. Important parameters including initial thickness of the liquid sublayer, vapor clot length, vapor clot velocity and void fraction etc., are calculated from the Liu-Nariai model. The initial heater surface temperature is derived from the Jens- Lottes correlation. The transient changes of liquid sublayer thickness, surface temperature at DNB are reported. No obvious temperature jumping is observed at DNB. To predict temperate excursion at Critical Heat Flux (CHF), more simulations to the transient boiling and film boiling processes are needed.

Probing DNA Bending Kinetics by yNhp6A with Ultrafast Temperature Jump Spectroscopy

The yeast Nhp6A protein is a member of the eukaryotic HMGB family of chromatin factors that enhance apparent DNA flexibility in many cellular processes. yNhp6A exhibits no sequence-specificity but binds to DNA with 1-10 nM affinity, sharply bending the DNA by >60° at the binding site. The kinetic mechanism by which this DNA deformation occurs remains unclear. It is not known whether the protein first binds weakly to unbent DNA and then deforms the DNA or if partially bent DNA conformations are thermally accessible and are “captured” and stabilized by the bound protein. The limited (tens-of-milliseconds) time resolution of previous kinetics studies was insufficient to observe the dynamics of DNA deformations in this complex. Here, we report time-resolved FRET measurements on yNhp6A bound to an 18-bp DNA oligomer labeled at each end with Cy3/Cy5, in response to a laser temperature-jump (T-jump) perturbation. The us temporal resolution of T-jump, together with ionic-strength and concentration dependence of equilibrium FRET and anisotropy measurements, helps reveal some of the microscopic kinetics steps. Equilibrium measurements with varied Nhp6A-DNA concentrations indicate that, at 250mM NaCl, the decrease in FRET with increasing temperature, in the range 15-60°C, is from unimolecular unbending of DNA. Kinetics traces measured under these salt conditions are single-exponential with relaxation times ranging from ∼400 us (at 60°C) to ∼1ms (at 45°C). At lower [salt] 65°C, bi-exponential kinetics are observed, likely corresponding to unimolecular bending/unbending, followed by dissociation of the complex and concurrent DNA melting. These results represent the first observation of DNA bending/unbending dynamics in complex with a nonspecific DNA-binding protein, and are an important step towards a more comprehensive understanding of the kinetic mechanisms of DNA binding and bending interactions by this class of proteins.

レーザー温度ジャンプ型過渡透過光計測法による温度応答性高分子水溶液の相分離ダイナミクスの研究

レーザー温度ジャンプ型過渡透過光計測法による温度応答性高分子水溶液の相分離ダイナミクスの研究

Ensemble inequivalence in a mean-field XY model with ferromagnetic and nematic couplings.

We explore ensemble inequivalence in long-range interacting systems by studying an XY model of classical spins with ferromagnetic and nematic coupling. We demonstrate the inequivalence by mapping the microcanonical phase diagram onto the canonical one, and also by doing the inverse mapping. We show that the equilibrium phase diagrams within the two ensembles strongly disagree within the regions of first-order transitions, exhibiting interesting features like temperature jumps. In particular, we discuss the coexistence and forbidden regions of different macroscopic states in both the phase diagrams.

Sphingosine 1-Phosphate Induces Erythrocytes Sickling in Sickle Cell Disease By Promoting Hemoglobin S Aggregation

Sickle cell disease (SCD) is a genetic hemolytic disease with high morbidity and mortality affecting millions of individuals worldwide. Although SCD was identified a century ago, we still lack effective mechanism-based therapies to treat this disease. Our recent study showed inhibition of sphingosine kinase 1 (Sphk1, the enzyme that produces S1P) significantly decreased S1P level in sickle erythrocytes, attenuated sickling cells. We also found sickling was induced by high concentration (10µM) but not low concentration (0.5 µM) of S1P, which indicates S1P induced sickling is independent of its receptors. However, the mechanism of S1P inducing sickling in SCD is unknown. Because sickling is induced by formation of polymers of deoxygenated sickle hemoglobin, we hypothesized that S1P functions intracellularly to induce sickling by directly promoting polymerization of deoxygenated HbS. To test this possibility, we determined the effects of S1P on deoxy-HbS polymerization using temperature jump method. We found that 5µM S1P began to induce aggregation of deoxy-HbS (0.25mM) with shorter delay time at 17.65 ± 0.57min compared to HbS treated with solvent (methanol) which with delay time at 19.28 ± 0.17 min. Moroever, S1P at 10µM induced deoxy-HbS aggregation with further decreased delay time at 15.71 ± 0.38 min, clearly demonstrating a dose-dependent effect. Thus, this study indicates that S1P at concentrations higher than 5µM dramatically and specifically accelerated HbS aggregation. Next, we found that aggregation amplitude (ΔA) of deoxy-HbS was significantly increased by S1P at a concentration of 5µM and was further elevated at 10mM of S1P. indicating that S1P enhanced polymerization ability of deoxy-HbS in a dosage-dependent manner. Finally, we detected the effect of S1P on deaggregation of aggregated deoxy-HbS. We found that S1P significantly reduced temperature drop-mediated unaggregated HbS and this effect was in a dosage dependent manner. In order to test whether anti-sickling drug can increase delay time of Hb S aggregation, we chose 5-HMF that was reported anti-sickling. We found 5-HMF significantly increased delay time of HbS. Taken together, we demonstrated that S1P induces HbS polymerization via three mechanisms: 1) Accelerating polymerization of HbS by shortening temperature jump-mediated delay time; 2) enhancing the aggregate formation during temperature jumping; and 3) reducing deaggregation ability during temperature dropping. Thus, this study strongly supports our in vivo animal, in vitro cellular and functional evidence that S1P contributes to sickling by promoting polymerization. DisclosuresNo relevant conflicts of interest to declare.

Ultrafast cooling reveals microsecond-scale biomolecular dynamics.

The temperature-jump technique, in which the sample is rapidly heated by a powerful laser pulse, has been widely used to probe the fast dynamics of folding of proteins and nucleic acids. However, the existing temperature-jump setups tend to involve sophisticated and expensive instrumentation, while providing only modest temperature changes of ~10-15 °C, and the temperature changes are only rapid for heating, but not cooling. Here we present a setup comprising a thermally conductive sapphire substrate with light-absorptive nano-coating, a microfluidic device and a rapidly switched moderate-power infrared laser with the laser beam focused on the nano-coating, enabling heating and cooling of aqueous solutions by ~50 °C on a 1-μs time scale. The setup is used to probe folding and unfolding dynamics of DNA hairpins after direct and inverse temperature jumps, revealing low-pass filter behaviour during periodic temperature variations.

Creep of a nickel-based single-crystal superalloy during very high-temperature jumps followed by synchrotron X-ray diffraction

Complex thermomechanical loadings at high temperature (T⩾950°C) on the AM1 single-crystal superalloy were studied by X-ray diffraction under synchrotron radiation. This technique enables in situ access to the evolutions of the lattice mismatch as well as the volume fraction and the dislocation density of the γ and γ′ phases during high-temperature non-isothermal creep loadings. It is shown that the large microstructure evolutions through the growth/shrinkage of γ/γ′ interfaces due to the γ′ volume fraction changes and the associated variations in the density of dislocations at these interfaces during temperature jumps are key parameters controlling the whole behavior (distribution of internal stresses and constitutive laws) of both phases. We propose an empirical constitutive law linking the strain rate of the γ′ phase to its stress state as well as a way to determine it. During our experiments, the plastic behavior of the γ′-rafts is related to the entry of dislocations with Burgers vectors perpendicular to the tensile axis and controlled by the overcoming of a threshold stress corresponding to the internal stress components perpendicular to the tensile axis.

Intermodel variances of subtropical stratocumulus environments simulated in CMIP5 models

AbstractThis paper investigates simulation biases associated with the large‐scale environments of subtropical marine stratocumulus (Sc) in present climate simulations from the Coupled Model Intercomparison Project Phase 5 models. Comparison of eight major variables that strongly control the Sc clouds, including jumps of temperature and vapor across the inversion layer, indicates that these models all have similar shortcomings, such as overestimation of sensible and latent surface fluxes. The differences among the biases of these major variables between the Sc regions were also evaluated. Of all Sc regions, the Namibian Sc region showed the largest biases. The modeled simulation skill of the annual variation of low cloud cover (LCC) increases when the correlation coefficient between LCC and lower atmospheric stability is higher. This paper reemphasizes the importance, suggested in previous studies, of an improved relationship between lower tropospheric stability and LCC if we are to better predict annual variations in subtropical LCC.

Solar Radiation Effects on Cu–Water Nanofluid Flow over a Stretching Sheet with Surface Slip and Temperature Jump

In the present study, hydromagnetic convective flow and heat transfer of an absorbing and electrically conducting Cu–water nanofluid over a semi-infinite, ideally transparent, permeable stretching sheet due to solar radiation is considered. The flow considered is under both surface and thermal slip conditions. The governing equations are transformed into a nonlinear ordinary differential equations using classical Lie group approach which are solved numerically by means of the efficient numerical shooting technique with fourth-order Runge–Kutta scheme. The effects of involved parameters on the velocity and temperature profiles, skin friction and Nusselt number are examined and discussed through graphs and tables. Comparisons with previously published works are performed, and excellent agreement between the results is obtained.

Direct evidence of catalytic heterogeneity in lactate dehydrogenase by temperature jump infrared spectroscopy.

Protein conformational heterogeneity and dynamics are known to play an important role in enzyme catalysis, but their influence has been difficult to observe directly. We have studied the effects of heterogeneity in the catalytic reaction of pig heart lactate dehydrogenase using isotope edited infrared spectroscopy, laser-induced temperature jump relaxation, and kinetic modeling. The isotope edited infrared spectrum reveals the presence of multiple reactive conformations of pyruvate bound to the enzyme, with three major reactive populations having substrate C2 carbonyl stretches at 1686, 1679, and 1674 cm–1, respectively. The temperature jump relaxation measurements and kinetic modeling indicate that these substates form a heterogeneous branched reaction pathway, and each substate catalyzes the conversion of pyruvate to lactate with a different rate. Furthermore, the rate of hydride transfer is inversely correlated with the frequency of the C2 carbonyl stretch (the rate increases as the frequency decreases), consistent with the relationship between the frequency of this mode and the polarization of the bond, which determines its reactivity toward hydride transfer. The enzyme does not appear to be optimized to use the fastest pathway preferentially but rather accesses multiple pathways in a search process that often selects slower ones. These results provide further support for a dynamic view of enzyme catalysis where the role of the enzyme is not just to bring reactants together but also to guide the conformational search for chemically competent interactions.

Temperature-modulation spectroscopy of non-equilibrium systems

In order to devise experiments which give information on the structure of the free energy landscape (FEL), we present a theoretical framework to handle the temperature-modulation spectroscopy. We first test the superposition rule which serves as a basic principle of the linear response analysis of the temperature modulation. To this end, we exploit a simple two-state system and show that the response to a step modulation can be represented by the difference of two relaxations against two different temperature jumps. We also show that the response can be described by a properly defined effective temperature.

Phonon ballistic-diffusive heat conduction in silicon nanofilms by Monte Carlo simulations

Abstract An efficient Monte Carlo (MC) method on the basis of introducing a model of phonon scattering processes is proposed to simulate the ballistic-diffusive heat conduction in silicon nanofilms. The calculated thermal conductivity of nanofilms agrees with the experimental data, which is indicative of the validity of our simulations. The boundary temperature jump caused by the effects of phonon ballistic transport is observed by the MC technique. It is found that the boundary temperature jump increases with the Knudsen number (Kn). Theoretical models for predicting the boundary temperature jumps are also derived from the phonon Boltzmann transport equation. Model 1 is derived based on the acoustically thin approximation (Kn ≫ 1), whereas model 2 is obtained by the diffusive approximation (Kn ≪ 1). Furthermore, we derive model 3 in the intermediate region by an empirical way i.e. averaging model 1 and model 2. The theoretical models agree well with the MC simulations in different regions.

Boundary layer depth: sensitivity study

The planetary boundary layer (PBL) height calculation is a two–step process. In the first one, the turbulence characteristics are evaluated either from direct measurements or through parameterisation schemes that use indirect measurements. In the second one, the PBL height is calculated using a model. For the convective PBL, simple models consider two parameters: the height and the temperature jump of the elevated inversion. The solution of two differential equations that couple those two parameters to the atmospheric turbulence properties gives the time evolution of the PBL height. For the stable case, simpler expressions are used; they relate the height of the PBL to the mechanical turbulence parameter u*. The results of different methods of evaluating the more significant turbulence parameters for the PBL height calculation are analysed and compared.

X-RAY OBSERVATIONS OF COMPLEX TEMPERATURE STRUCTURE IN THE COOL-CORE CLUSTER A85

X-ray observations were used to examine the complex temperature structure of Abell 85, a cool-core galaxy cluster. Temperature features can provide evidence of merging events which shock heat the intracluster gas. Temperature maps were made from both \textit{Chandra} and \textit{XMM-Newton} obervations. The combination of a new, long-exposure \textit{XMM} observation and an improved temperature map binning technique produced the highest fidelity temperature maps of A85 to date. Hot regions were detected near the subclusters to the South and Southwest in both the \textit{Chandra} and \textit{XMM} temperature maps. The presence of these structures implies A85 is not relaxed. The hot regions may indicate the presence of shocks. The Mach numbers were estimated to be $\sim$1.9 at the locations of the hot spots. Observational effects will tend to systematically reduce temperature jumps, so the measured Mach numbers are likely underestimated. Neither temperature map showed evidence for a shock in the vicinity of the presumed radio relic near the Southwest subcluster. However, the presence of a weak shock cannot be ruled out. There was tension between the temperatures measured by the two instruments.