Kinetic melting and crystallization stages of strongly superheated and supercooled metals

The heterogeneous melting/crystallization of metals with different crystallographic lattices in conditions where the phase front propagates on overheated/supercooled media was modeled in the context of the molecular dynamics approach. In order to obtain the temperature dependence of the kinetic velocity in analytical form, the results of atomistic modeling were approximated by the function obtained from the kinetic representations. For the first time, stationary temperature dependences of kinetic velocity ν(T _s ?) for the limit values of superheated/supercooled copper and iron were built.     

Alloy design of a cost-effective and castable heat-resistant iron alloy

A new heat-resistant Fe-based cast alloy has been designed making the best use of the CALPHAD method. The objective was to replace the material for precision cast products made from Ni-based superalloys with improved Fe-based alloys originally developed for lower temperature applications.The key to the design is to balance the amount of strengthening ${\gamma }^{\prime }$- Ni₃(Ti,Al) precipitates and brittle $\sigma$ phase, and to simultaneously decrease as-cast microsegregation. Contours of the equal phase fraction were calculated over the isothermal diagrams of the Fe–Ni–Cr–Ti–Al–Nb system, and provided useful guidelines for compositional modifications. The microsegregation was also evaluated by Scheil-type simulation in order to reduce micropores caused by oxidation of the solidifying front.The developed cast Fe-based alloy showed desirable strength at the envisioned service temperatures and filled the open range of heat resistance between Ni-based superalloys and the original alloy.     

Viscous Taylor droplets in axisymmetric and planar tubes: from Bretherton’s theory to empirical models

The aim of this study is to derive accurate models for quantities characterizing the dynamics of droplets of non-vanishing viscosity in capillaries. In particular, we propose models for the uniform-film thickness separating the droplet from the tube walls, for the droplet front and rear curvatures and pressure jumps, and for the droplet velocity in a range of capillary numbers, Ca, from \(10^{-4}\) to 1 and inner-to-outer viscosity ratios, \(\lambda\), from 0, i.e. a bubble, to high-viscosity droplets. Theoretical asymptotic results obtained in the limit of small capillary number are combined with accurate numerical simulations at larger Ca. With these models at hand, we can compute the pressure drop induced by the droplet. The film thickness at low capillary numbers (\(Ca<10^{-3}\)) agrees well with Bretherton’s scaling for bubbles as long as \(\lambda <1\). For larger viscosity ratios, the film thickness increases monotonically, before saturating for \(\lambda>10^3\) to a value \(2^{2/3}\) times larger than the film thickness of a bubble. At larger capillary numbers, the film thickness follows the rational function proposed by Aussillous and Quéré (Phys Fluids 12(10):2367–2371, 2000) for bubbles, with a fitting coefficient which is viscosity-ratio dependent. This coefficient modifies the value to which the film thickness saturates at large capillary numbers. The velocity of the droplet is found to be strongly dependent on the capillary number and viscosity ratio. We also show that the normal viscous stresses at the front and rear caps of the droplets cannot be neglected when calculating the pressure drop for \(Ca>10^{-3}\).     

Remote optical observation of biomass burning: A feasibility and experimental case study with the SIM.GA hyperspectral system

In this article, the feasibility of detecting fire fronts from biomass burning, using the HYPER/SIM.GA system (Galileo Avionica Multisensor Hyperspectral System), has been tested. This system includes two hyperspectral optical heads, in the Visible and near-infrared (VNIR) and Short-wave infrared (SWIR) bands, providing complete spectral coverage from the visible (0.4 μm) to the thermal infrared (24 μm) bands.

We revised the strategies to detect the fire front from hyperspectral data. We found that the radiance emitted by potassium atoms (K) at 766.5 and 769.9 nm, electronically excited during biomass burning, can be usefully exploited to detect the fire front. A study has been made, in order to verify the sensitivity of this feature to biomass composition, fire temperature and visibility. A typical scenario, in which a wildland fire takes place, has been simulated. Simulated data have been compared with real data, confirming the feasibility of this approach to detect the fire front.

This approach is advantageous, both from the economic and operative viewpoints, with respect to classical remote sensing for fire detection, usually based on the Planck emission at thermal bands.     

Quantum discord in spin systems with dipole–dipole interaction

The behavior of total quantum correlations (discord) in dimers consisting of dipolar-coupled spins 1/2 are studied. We found that the discord $Q=0$ at absolute zero temperature. As the temperature $T$ increases, the quantum correlations in the system increase at first from zero to its maximum and then decrease to zero according to the asymptotic law $T^{-2}$ . It is also shown that in absence of external magnetic field $B$ , the classical correlations $C$ at $T\rightarrow 0$ are, vice versa, maximal. Our calculations predict that in crystalline gypsum $\hbox {CaSO}_{4}\cdot \hbox {2H}_{2}{\hbox {O}}$ the value of natural $(B=0)$ quantum discord between nuclear spins of hydrogen atoms is maximal at the temperature of 0.644  $\upmu $ K, and for 1,2-dichloroethane $\hbox {H}_{2}$ ClC– $\hbox {CH}_{2}{\hbox {Cl}}$ the discord achieves the largest value at $T=0.517~\upmu $ K. In both cases, the discord equals $Q\approx 0.083$  bit/dimer what is $8.3\,\%$ of its upper limit in two-qubit systems. We estimate also that for gypsum at room temperature $Q\sim 10^{-18}$  bit/dimer, and for 1,2-dichloroethane at $T=90$  K the discord is $Q\sim 10^{-17}$  bit per a dimer.     

Psychological impact of air velocity variations in a ventilated room

Two experiments investigated the psychological impact of two velocity conditions (constant low velocity (V1) and variations of low and high velocity (V2)) in two temperature conditions (Experiment 1: an air temperature increase from 21°C to 24°C; Experiment 2: an air temperature increase from 25°C to 27°C) in females and males, aged 16 to 18 years, under realistic classroom conditions during an exposure period of 80 min. It was predicted that the V2 room condition compared to the V1 room condition would be more beneficial for subjects' perceived room temperature and air quality, self-reported affect and cognitive performance. The results obtained showed no significant effects on cognitive performance. However and as predicted, in Experiment 1, the subjects in the V2 compared to those in the V1 room condition felt that the air temperature decreased (while it de facto increased) and reported a constant level of high activation. In Experiment 2, the subjects in the V2 room condition felt that the air temperature increased less and reported that their unactivated unpleasantness increased less and activated pleasantness decreased less than it did for subjects in the V1 room condition. All this indicates, as was suggested by Wigö et al. (2002 Wigö, H., Knez, I. and Sandberg, M. 2002. Effects of velocity variations in ventilated room on comfort, affect and cognitive performance. Proceedings of 9th International Conference on Indoor Air Quality and Climate, 4: 635–640.  [Google Scholar]), that a cooling effect, induced by air velocity variations, might be beneficial for subjects in a ventilated room and that their perceived pleasantness of the indoor climate could be met at a higher room temperature than otherwise.     

Thermal entanglement of the mixed spin-1/2 and spin-5/2 Heisenberg model under an external magnetic field

We use the concept of negativity to study the entanglement of spin-1/2 and spin-5/2 antiferromagnetic Heisenberg model with an inhomogeneous magnetic field. Analytical conclusions of the model are acquired. It is found that the critical temperature \(T_\mathrm{c}\) goes up, as the increase of anisotropy parameter \(k\) . The temperature \(T_\mathrm{c}\) becomes bigger than the results of spin-1/2 and spin-3/2 Heisenberg XXZ chain for the same value of \(k\) . And we can gain more entanglement at higher temperature by coordinating the value of inhomogeneity \(b\) .     

Fast Object Segmentation by Growing Minimal Paths from a Single Point on 2D or 3D Images

In this paper, we present a new method for segmenting closed contours and surfaces. Our work builds on a variant of the minimal path approach. First, an initial point on the desired contour is chosen by the user. Next, new keypoints are detected automatically using a front propagation approach. We assume that the desired object has a closed boundary. This a-priori knowledge on the topology is used to devise a relevant criterion for stopping the keypoint detection and front propagation. The final domain visited by the front will yield a band surrounding the object of interest. Linking pairs of neighboring keypoints with minimal paths allows us to extract a closed contour from a 2D image. This approach can also be used for finding an open curve giving extra information as stopping criteria. Detection of a variety of objects on real images is demonstrated. Using a similar idea, we can extract networks of minimal paths from a 3D image called Geodesic Meshing. The proposed method is applied to 3D data with promising results.

A Weak Galerkin Method with an Over-Relaxed Stabilization for Low Regularity Elliptic Problems

A new weak Galerkin (WG) finite element method is developed and analyzed for solving second order elliptic problems with low regularity solutions in the Sobolev space \(W^{2,p}(\Omega )\) with \(p\in (1,2)\). A WG stabilizer was introduced by Wang and Ye (Math Comput 83:2101–2126, 2014) for a simpler variational formulation, and it has been commonly used since then in the WG literature. In this work, for the purpose of dealing with low regularity solutions, we propose to generalize the stabilizer of Wang and Ye by introducing a positive relaxation index to the mesh size h. The relaxed stabilization gives rise to a considerable flexibility in treating weak continuity along the interior element edges. When the norm index \(p\in (1,2]\), we strictly derive that the WG error in energy norm has an optimal convergence order \(O(h^{l+1-\frac{1}{p}-\frac{p}{4}})\) by taking the relaxed factor \(\beta =1+\frac{2}{p}-\frac{p}{2}\), and it also has an optimal convergence order \(O(h^{l+2-\frac{2}{p}})\) in \(L^2\) norm when the solution \(u\in W^{l+1,p}\) with \(p\in [1,1+\frac{2}{p}-\frac{p}{2}]\) and \(l\ge 1\). It is recovered for \(p=2\) that with the choice of \(\beta =1\), error estimates in the energy and \(L^2\) norms are optimal for the source term in the sobolev space \(L^2\). Weak variational forms of the WG method give rise to desirable flexibility in enforcing boundary conditions and can be easily implemented without requiring a sufficiently large penalty factor as in the usual discontinuous Galerkin methods. In addition, numerical results illustrate that the proposed WG method with an over-relaxed factor \(\beta (\ge 1)\) converges at optimal algebraic rates for several low regularity elliptic problems.     

Quantum-memory-assisted entropic uncertainty in two-qubit Heisenberg <Emphasis Type="Italic">XYZ</Emphasis> chain with Dzyaloshinskii–Moriya interactions and effects of intrinsic decoherence

Quantum-memory-assisted entropic uncertainty relation (QMA-EUR) in two-qubit Heisenberg XYZ spin chain model with Dzyaloshinskii–Moriya (DM) interaction has been investigated. The paper shows that the DM interactions and the spin interactions alone x, y, z directions can efficiently suppress the entropic uncertainty of Pauli observables (\(\sigma _{x}\) and \(\sigma _{z}\)), even make the entropic uncertainty close to zero. As well, it is pointed out that the entropic uncertainty reaches to zero at very low temperature, starts to increase with temperature after a threshold, and generally becomes constant at a fixed value. We also verified the Bob’s uncertainty about Alice’s measurement outcomes is anticorrelated with the sum of the accessible information of observer. Furthermore, the decoherence conditions including dephasing and noisy environments are considered. For the fixed initial state, the entropic uncertainty of the XYZ model with DM interaction in z-direction are independent of spin–spin coupling \(J_z\) and the anisotropy parameter \(\varDelta \). In the dephasing environment, the evolutions of entropic uncertainty and its lower bound \(U_{B}\) oscillate with the time and saturates at a finite value, and this value is varied with the purity parameter r of initial state. In the noisy environment, the entropic uncertainty and its lower bound monotonically increase with the time and will be stable at value 2 quickly. This is because the combined effects of the DM interaction and the decoherence force the various initial entanglement states to oscillate into an identical state, regardless of the value of \(D_{z}\) and the parameter r of initial state.     

On rheological characteristics of non-Newtonian nanofluids in the material forming process

In this paper, the material forming process (such as that of the functionally graded materials) of adding nanoparticles into non-Newtonian fluids is considered. By adding nanoparticles to a non-Newtonian fluid, a new non-Newtonian fluid is created. Thus, the rheological characteristics of the original fluid matrix have been changed. This research attempts to consider the influence of the rheological characteristics combined with the Brownian diffusion, and the thermophoresis diffusion, the distribution of nano-sized particles, the heat transfer, and the pressure drop on the process of material formation. The configuration of material treatment process is an H-height horizontal parallel plate channel with laminar forced convection nanofluids-based non-Newtonian fluids flowing through. The channel is separated by three different boundary conditions: heating, cooling, and isolated, to simulate the melting, the freezing, and the flowing processes of materials in liquid form. The non-Newtonian behaviour of nanofluids is described by the power-law model. To highlight the rheological factors of power-law nanofluids which are not the same as those of the base non-Newtonian fluids, they are assumed to vary with the quantity of the added nanoparticles in the fluid matrix, that is to say, both the consistency coefficient \(m\) and the power-law index \(n\) are considered as functions of particle loading parameter \(\phi\). Two sets of different functions of consistency coefficient \(m\) and power-law index \(n\) are used and compared in the later calculation. Method of finite element is adopted to solve the coupled momentum, energy and concentration equations, and conquer the difficulties arsing in the iteration of calculation. It is found that whether the rheological factors of non-Newtonian nanofluids are considered changeable or not would lead to very different results of the mass transfer. Also, as the parameter \(N_{\text{T}}\) (depicting the thermophoresis diffusion) increases, both temperature and concentration profiles rise, while volume fraction of particles and temperature both fall as \(N_{\text{B}}\) number (presenting the Brownian diffusion) increases. Furthermore, when two models are compared, different rheological models may possess different change rule of power-law index, but in both rheological models, the diversification of power-law index is so large that it cannot be ignored in calculation. Above all, the detailed information of velocity, temperature, and pressure drop obtained by rheological models highlights the necessity of studying the impact of rheological characteristics of non-Newtonian fluids in elaborate industrial requirements.     

A method to retrieve subpixel fire temperature and fire area using MODIS data

Methods for retrieving subpixel fire temperature and fire area have been developed over several years, but the retrieval accuracies of these methods require further improvement. In this study, a channel of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor centred at 2.1 μm and associated with the MODIS 4.0 2.1 μm channel is used to retrieve the temperature and area of fires. To test the feasibility of using the 2.1 μm channel for retrieval, the fire contribution ratios of MODIS 2.1, 4.0 and 11.0 μm channels are first examined using simulated surface radiance. Considering the difficulties in obtaining real-time validation data and in evaluating the retrieval accuracies, simulated MODIS data are used for this study. A modified method, which combines MODIS 2.1 and 4.0 μm channels, is introduced and described in detail. Compared with the traditional method, which utilizes a combination of 4.0 and 11.0 μm channels (Dozier 1981 Dozier, J. 1981. A method for satellite identification of surface temperature fields of subpixel resolution. Remote Sensing of Environment, 11: 221–229. [Crossref], [Web of Science ®] , [Google Scholar]), the results show that the 2.1 μm channel is more sensitive to active fires and the large area of fires than the 11.0 μm channel, but is less sensitive to smouldering fires and small fires. The modified method that we propose has better performance and higher accuracy in active fires (temperature ≥ 800 K) and in large fires (area ≥ 0.5%). However, the traditional method is more accurate for smouldering fires and small fires. Finally, a sensitivity analysis is performed to estimate the uncertainty in assessing fire temperature and area. Experimental results indicate that under realistic conditions (fire temperatures of approximately 1000 K and a fire fractional area greater than 0.005), the retrieval errors for fire temperature and fire area are ±35 K and 20%, respectively.     

Stability of a Hot Smoluchowski Fluid

We study coupled nonlinear parabolic equations for a fluid described by a material density and a temperature , both functions of space and time. In one dimension, we find some stationary solutions corresponding to fixing the temperature on the boundary, with no-escape boundary conditions for the material. For the special case, where the temperature on the boundary is the same at both ends, the linearized equations for small perturbations about a stationary solution at uniform temperature and density are derived; they are subject to boundary conditions, Dirichlet for and no-flow conditions for the material. The spectrum of the generator L of time evolution, regarded as an operator on L ², is shown to be real, discrete and non-positive, even though L is not self-adjoint. This result is necessary for the stability of the stationary state, but might not be sufficient. The problem lies in the fact that L is not a sectorial operator, since its numerical range is C.