Asymptotic models and inference for extremes of spatio-temporal data

Recently there has been a lot of effort to model extremes of spatially dependent data. These efforts seem to be divided into two distinct groups: the study of max-stable processes, together with the development of statistical models within this framework; the use of more pragmatic, flexible models using Bayesian hierarchical models (BHM) and simulation based inference techniques. Each modeling strategy has its strong and weak points. While max-stable models capture the local behavior of spatial extremes correctly, hierarchical models based on the conditional independence assumption, lack the asymptotic arguments the max-stable models enjoy. On the other hand, they are very flexible in allowing the introduction of physical plausibility into the model. When the objective of the data analysis is to estimate return levels or kriging of extreme values in space, capturing the correct dependence structure between the extremes is crucial and max-stable processes are better suited for these purposes. However when the primary interest is to explain the sources of variation in extreme events Bayesian hierarchical modeling is a very flexible tool due to the ease with which random effects are incorporated in the model. In this paper we model a data set on Portuguese wildfires to show the flexibility of BHM in incorporating spatial dependencies acting at different resolutions.     

Single Crystal Refinement of the Incommensurately Modulated Mn0.55Ta0.45O1.7, an Oxygen Deficient Fluorite Type Compound

A structural investigation of the incommensurately ordered compound Mn_0.55Ta_0.45O_1.7 has been carried out, using single‐crystal X‐ray diffraction data. The basic structure is related to the fluorite type with a monoclinic distortion. Electron diffraction (ED) patterns for various crystal orientations were used for determination of unit cell, incommensurate modulation vector and superspace group. The unit cell parameters and the length and direction of the incommensurate vector were refined using X‐ray powder diffraction (XRPD) data. P2/m was chosen as the three‐dimensional space group for a subcell with parameters a = 3.5005(2) Å (√2/2 · a_f), b = 3.5730(2) (√2/2 · a_f), c = 5.0015(2) Å (a_f) and β = 91.677(7)°. From the systematic absences hklm: k + m ≠ 2n, the four‐dimensional superspace group was determined to be B : P2/m(α 0 c) with determined modulation vector components α = –0.1833(1) and γ = 0.3582(2). A total of 511 unique reflections (79 basic fluorite type, 268 first‐order and 164 second‐order satellites) were used in the structure refinement, which resulted in weighted R‐values of 5.6% for the fluorite type sublattice reflections, 5.5% for the first‐order satellites and 7.4% for the second‐order satellites. The Mn and Ta atoms were found to be both positionally and occupationally modulated and the oxygen atoms to be highly disordered. The structure is the first fluorite‐related modulated structure of an oxide that has been determined from single‐crystal data. The structural relation to the previously characterised disordered cubic phase Mn_0.6Ta_0.4O_1.65 and the diffuse scattering exhibited by it are discussed in the article.     

Heat removal from oscillating flow in a vertical annular channel

In this study, heat removal from a surface, which is located into the reciprocating flow in a vertical annular liquid column, is investigated experimentally. The experiments are carried out for four different oscillation frequencies and three heat fluxes while the amplitude remains constant for all cases. Instantaneous and time-averaged surface and bulk temperature variations are presented. The cycle-averaged values are considered in the calculation of heat transfer using the experimental measurements. Heat removal from the cold surface due to the oscillating liquid column is determined in terms of Nusselt number. Based on the experimental data, an empirical equation is obtained for the cycle averaged Nusselt number as a function of kinetic Reynolds number.     

Estimation of solubility parameter by the modified ER equation of state

The applications of the solubility parameter in chemical, petroleum and polymer engineering industries have been cleared up along the past 50 years. In this article, the Hildebrand solubility parameter of over 250 substances were calculated by the modified ER (Esmaeilzadeh–Roshanfekr) equation of state and some others (the Peng–Robinson, Soave–Redlich–Kwong, Patel–Teja and Schmidt–Wenzel) and compared with the experimental data. Once the less average errors of the mER method predictions were satisfied in subcritical and some supercritical fluids region, a correlation based on this EOS was presented in order to calculate the total HSP (Hansen solubility parameter) of various types of organic components categorized in 13 distinct groups including paraffins, olefins, aromatics, naphthenes, alcohols, aldehydes, ketones, ethers, esters, amines, carboxylic acids and two petroleum sub-fractions (resins and asphaltenes). The optimal values of the model parameters were obtained applying the DE (differential evolution) optimization method. The absolute average deviations of the proposed correlations results from the experimental ones lied between 0.09 and 6%.     

Electrohydrodynamic conduction pumps with cylindrical electrodes for pumping of dielectric liquid film in an open channel

In the present study, electrohydrodynamic conduction pumping of n-hexane and n-decane liquid films in an open channel has been investigated experimentally. These two dielectric liquids have nearly the same electrical properties but with their different viscosities. The effects of film thicknesses, the arrangement of electrodes and the gap between pumps on the flow rate of liquid films have been also studied. The pumps with cylindrical electrodes have been installed in the channel. The best performance of the conduction pumps, revealing with experimental results, has been achieved at 8 mm thickness of liquid film with the gap size of 55 mm for both dielectric liquids in the present layout of the pumps.     

A numerical study of turbulent opposed impinging jets issuing from triangular nozzles with different geometries

In present research, two turbulent opposed impinging air jets issuing from triangular nozzles with fixed and variable exit velocity ratios and different nozzle-to-nozzle distances have been studied numerically and then compared with rectangular and circular nozzles. The finite volume method has been applied for solving mass and momentum equations. The turbulence model being used here is k-ε RNG. Distributions of pressure, turbulence, kinetic energy and its dissipation rate in various regions especially on the impingement regions have been obtained with high accuracy. Study of the nozzle geometries has shown the advantage of triangular nozzles over other geometries. First, the triangle’s base in nozzle geometry has an important role in our study case which, mixing two flows and regions with high turbulence intensity, directly depends on it. Second, our results show that circular and rectangular nozzles have less efficiency than triangular nozzles in mixing applications. Third and last, it was found that the radial jet being created by opposed jets has some similarities to free jets. In this investigation, air in standard atmospheric pressure has been applied as working fluid.     

An experimental investigation of polyacrylamide and sulfonated polyacrylamides based gels crosslinked with cr(III)-acetate for water shutoff in fractured oil reservoirs

Abstract

Water injection as one of the most efficient and worldwide extensively employed approach in homogenous oil reservoirs suffers from early water breakthrough time as well as low oil sweep efficiency values in fractured oil reservoirs. This study investigates the potential application of Cr(III)-acetate based gel polymer system in a typical water injection process using one fractured micromodel. For this purpose, three sulfonated polyacrylamides, different in solfunation degree, and one hydrolyzed polyacrylamide were studied regarding gelation time, gel strength and stability to find the optimized conditions in terms of polymer type and concentration, and polymer/Cr(III)-acetate ratio, which were subsequently used for one dynamic test. Results illustrated the optimized conditions as AN 105 polymer with concentration of 5000?ppm and polymer/Cr(III) ratio of 5. Moreover, results showed that implementing such gel system yields an increased oil recovery value of 24.46% OOIP at 1.55 PV and delays the breakthrough time from 0.47 PV to 0.51 PV.     

CVD grown 2D MoS2 layers: A photoluminescence and fluorescence lifetime imaging study

In this letter, we report on the fluorescence lifetime imaging and accompanying photoluminescence properties of a chemical vapour deposition (CVD) grown atomically thin material, MoS₂. µ‐Raman, µ‐photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) are utilized to probe the fluorescence lifetime and photoluminescence properties of individual flakes of MoS₂ films. Usage of these three techniques allows identification of the grown layers, grain boundaries, structural defects and their relative effects on the PL and fluorescence lifetime spectra. Our investigation on individual monolayer flakes reveals a clear increase of the fluorescence lifetime from 0.3 ns to 0.45 ns at the edges with respect to interior region. On the other hand, investigation of the film layer reveals quenching of PL intensity and lifetime at the grain boundaries. These results could be important for applications where the activity of edges is important such as in photocatalytic water splitting. Finally, it has been demonstrated that PL mapping and FLIM are viable techniques for the investigation of the grain‐boundaries.

     

Characteristics of the breakup and fragmentation of an electrohydrodynamic melt jet

In this study, the breakup of a melt jet into a viscous medium is investigated in the presence of an intense electric field. Fragmentation of the melt jet occurs due to both hydrodynamic and electrohydrodynamic (EHD) forces within two kinds of silicone oil of different viscosities. The size and shape characteristics of the produced particles have been studied using SEM images, and the particle size distributions were found to exhibit considerable variations when a voltage was applied and when both the viscosity and temperature of the base fluid were changed. The morphologies of the particles were also affected by the same parameters. For instance, by applying EHD force, significant enhancements in size reduction and increased roundness of the particles occurred. The breakup process of the melt jet was found to be dominant by hydrodynamic or electrohydrodynamic instabilities, depending on the situation. Governing mechanisms (instability) in the cases of pure hydrodynamic and electrohydrodynamic fragmentations are discussed.