Abstract: This work contributes to a new generalized empirical correlation for predicting methane (CH4) hydrate equilibrium conditions in pure water. Unlike the conventional thermodynamic approach that involves complex reckoning, the proposed empirical equation is developed by regressing 215 experimental data points from the literature and validating with 45 data points for predicting methane hydrate equilibrium conditions in pure water. The new correlation is proposed for a temperature and pressure range of 273.2–303.48 K and 2.63–72.26 MPa, respectively. The accuracy and performance of the proposed correlation is quantitatively evaluated using statistical error analysis. The proposed correlation was able to estimate CH4 hydrate equilibrium conditions satisfactorily with an R2 of 0.99987. The overall error analysis for the proposed correlation shows fair agreement with the experimental data reported within the literature. Concurrently, the new correlation showed better performance in predicting equilibrium conditions compared to those calculated by other empirical correlations available in the literature within the investigated range. In addition, the proposed empirical equation is also checked to evaluate its efficacy in fitting each set of experimental binary/ternary methane hydrates (BTMH) and binary hydrogen hydrates (BHH) for an accurate representation of equilibrium data over a wide range of composition, pressure, and temperature conditions. A maximum percentage deviation of 0.58% and 0.24% was observed between experimental and calculated equilibrium conditions for BTMH and BHH, respectively.

Abstract: High-performance rechargeable batteries are becoming very important for high-end technologies with their ever increasing application areas. Hence, improving the performance of such batteries has become the main bottleneck to transferring high-end technologies to end users. In this study, we propose an argon intercalation strategy to enhance battery performance via engineering the interlayer spacing of honeycomb structures such as graphite, a common electrode material in lithium-ion batteries (LIBs). Herein, we systematically investigated the LIB performance of graphite and hexagonal boron nitride (h-BN) when argon atoms were sent into between their layers by using first-principles density-functional-theory calculations. Our results showed enhanced lithium binding for graphite and h-BN structures when argon atoms were intercalated. The increased interlayer space doubles the gravimetric lithium capacity for graphite, while the volumetric capacity also increased by around 20% even though the volume was also increased. The ab initio molecular dynamics simulations indicate the thermal stability of such graphite structures against any structural transformation and Li release. The nudged-elastic-band calculations showed that the migration energy barriers were drastically lowered, which promises fast charging capability for batteries containing graphite electrodes. Although a similar level of battery promise was not achieved for h-BN material, its enhanced battery capabilities by argon intercalation also support that the argon intercalation strategy can be a viable route to enhance such honeycomb battery electrodes.

Abstract: We determine the energy of an interface between a multiband superconducting and a normal half-space, in presence of an applied magnetic field, based on a multiband Ginzburg-Landau (GL) approach. We obtain that the multiband surface energy is fully determined by the critical temperature, electronic densities of states, and superconducting gap functions associated with the different band condensates. This furthermore yields an expression for the thermodynamic critical magnetic field, in presence of an arbitrary number of contributing bands. Subsequently, we investigate the sign of the surface energy as a function of material parameters, through numerical solution of the GL equations. Here, we consider two distinct cases: (i) standard multiband superconductors with attractive interactions, and (ii) a three-band superconductor with a chiral ground state with phase frustration, arising from repulsive interband interactions. Furthermore, we apply this approach to several prime examples of multiband superconductors, such as metallic hydrogen and MgB2, based on microscopic parameters obtained from first-principles calculations.

Abstract: Using atomistic magnetic simulations we investigate the soliton motion along a pinned skyrmion chain containing an interstitial skyrmion. We find that the soliton can exhibit stable motion along the chain without a skyrmion Hall effect for an extended range of drives. Under a constant drive the solitons have a constant velocity. We also measure the skyrmion velocity-current curves and identify the signatures of different phases including a pinned phase, stable soliton motion, and quasi-free motion at higher drives where all of the skyrmions depin from the pinning centers and move along the rigid wall. In the quasi-free motion regime, the velocity is oscillatory due to the motion of the skyrmions over the pinning sites. For increasing pinning strength, the onset of soliton motion shifts to higher values of current density. We also find that for stronger pinning, the characteristic velocity-current shape is affected by the annihilation of single or multiple skyrmions in the drive interval over which the soliton motion occurs. Our results indicate that stable skyrmion soliton motion is possible and that the solitons could be used as information carriers instead of the skyrmions themselves for technological applications.

Abstract: Preston's equation is a general model describing the egg shape of birds. The parameters of Preston's equation are usually estimated after re-expressing it as the Todd-Smart equation and scaling the egg's actual length to two. This method assumes that the straight line through the two points on an egg's profile separated by the maximum distance (i.e., the longest axis of an egg's profile) is the mid-line. It hypothesizes that the photographed egg's profile is perfectly bilaterally symmetrical, which seldom holds true because of photographic errors and placement errors. The existing parameter estimation method for Preston's equation considers an angle of deviation for the longest axis of an egg's profile from the mid-line, which decreases prediction errors to a certain degree. Nevertheless, this method cannot provide an accurate estimate of the coordinates of the egg's center, and it leads to sub-optimal parameter estimation. Thus, it is better to account for the possible asymmetry between the two sides of an egg's profile along its mid-line when fitting egg-shape data. In this paper, we propose a method based on the optimization algorithm (optimPE) to fit egg-shape data and better estimate the parameters of Preston's equation by automatically searching for the optimal mid-line of an egg's profile and testing its validity using profiles of 59 bird eggs spanning a wide range of existing egg shapes. We further compared this method with the existing one based on multiple linear regression (lmPE). This study demonstrated the ability of the optimPE method to estimate numerical values of the parameters of Preston's equation and provide the theoretical egg length (i.e., the distance between two ends of the mid-line of an egg's profile) and the egg's maximum breadth. This provides a valuable approach for comparing egg shapes among conspecifics or across different species, or even different classes (e.g., birds and reptiles), in future investigations.

Abstract: Infrared thermography is a fast, non-destructive and contactless testing technique which is increasingly used in heritage science. The aim of this study was to assess the ability of infrared thermography, in combination with a data clustering approach, to differentiate between the different types of historical glass that were included in a colorless leaded-glass windows during previous restoration interventions. Inspection of the thermograms and the application of two data mining techniques on the thermal data, i.e., k-means clustering and hierarchical clustering, allowed identifying different groups of window panes that show a different thermal behavior. Both clustering approaches arrive at similar groupings of the glass with a clear separation of three types. However, the lead cames that hold the glass panes appear to have a substantial impact on the thermal behavior of the surrounding glass, thus preventing classification of the smallest glass panes. For the larger panes, this was not a critical issue as the center of the glass remained unaffected. Subtle visual color differences between panes, implying a variation in coloring metal ions, was not always distinguished by IRT. Nevertheless, data clustering assisted infrared thermography shows potential as an efficient and swift method for documenting the material intervention history of leaded-glass windows during or in preparation of conservation treatments.

Abstract: Particulate matter (PM) deposition on urban green enables the collection of particulate pollution from a diversity of contexts, and insight into the physico-chemical profiles of PM is key for identifying main polluting sources. This study reports on the morphological and elemental characterization of PM2-10 deposited on ivy leaves from five different environments (forest, rural, roadside, train, industry) in the region of Antwerp, Belgium. Ca. 40,000 leaf-deposited particles were thoroughly investigated by particle-based analysis using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) and their physico-chemical characteristics were explored for PM source apportionment purposes. The size distribution of all deposited particles was biased towards small-sized PM, with 32% of the particles smaller than 2.5 mu m (PM2.5) and median diameters of 2.80-3.09 mu m. The source type influenced both the particles' size and morphology (aspect ratio and shape), with roadside particles being overall the smallest in size and the most spherical. While forest and rural elemental profiles were associated with natural PM, the industry particles revealed the highest anthropogenic metal input. PM2-10 profiles for roadside and train sites were rather comparable and only distinguishable when evaluating the fine (2-2.5 mu m) and coarse (2.5-10 mu m) PM fractions separately, which enabled the identification of a larger contribution of combustion-derived particles (small, circular, Fe-enriched) at the roadside compared to the train. Random forest prediction model classified the source type correctly for 61-85% of the leaf-deposited PM. The still modest classification accuracy denotes the influence of regional background PM and demands for additional fingerprinting techniques to facilitate source apportionment. Nonetheless, the obtained results demonstrate the utility of leaf particle-based analysis to fingerprint and pinpoint source-specific PM, particularly when considering both the composition and size of leaf-deposited particles.

Abstract: Forensic drug laboratories are confronted with increasing amounts of drugs and a demand for faster results that are directly available on-site. In addition, the drug market is getting more complex with hundreds of new psychoactive substances (NPS) entering the market in recent years. Rapid and on-scene presumptive drug testing therefore faces a shift from manual colorimetric tests towards approaches that can detect a wider range of components and process results automatically. Electrochemical detection offers these desired characteristics, making it a suitable candidate for on-site drug detection. In this study, a two-step electrochemical sensor is introduced for the detection of MDMA and 2C-B. Firstly, a direct electrochemical analysis was performed to detect MDMA. Validation experiments on over 70 substances revealed that 2C-B was the only frequently encountered drug that gave a false positive result for MDMA in this first analysis. A second step using in-situ derivatization was subsequently introduced. To this end, formaldehyde was used for N-methylation of 2C-B thereby enhancing its electrochemical profile. The enriched electrochemical fingerprint in the second step allowed for clear differentiation between MDMA and 2C-B. The applicability of this approach was demonstrated with 71 ecstasy tablets seized by the Amsterdam Police. The MDMA/2C-B sensor correctly identified all 39 MDMA-containing tablets and 10 out of 11 tablets containing 2C-B. Most notably, correct results were also obtained for dark colored tablets in which both spectroscopic analysis and colorimetric tests failed due to obscured signals.

Abstract: The Lamé curve is an extension of an ellipse, the latter being a special case. Dr. Johan Gielis further extended the Lamé curve in the polar coordinate system by introducing additional parameters (n1, n2, n3; m): rφ=1Acosm4φn2+1Bsinm4φn3−1/n1, which can be applied to model natural geometries. Here, r is the polar radius corresponding to the polar angle φ; A, B, n1, n2 and n3 are parameters to be estimated; m is the positive real number that determines the number of angles of the Gielis curve. Most prior studies on the Gielis equation focused mainly on its applications. However, the Gielis equation can also generate a large number of shapes that are rotationally symmetric and axisymmetric when A = B and n2 = n3, interrelated with the parameter m, with the parameters n1 and n2 determining the shapes of the curves. In this paper, we prove the relationship between m and the rotational symmetry and axial symmetry of the Gielis curve from a theoretical point of view with the condition A = B, n2 = n3. We also set n1 and n2 to take negative real numbers rather than only taking positive real numbers, then classify the curves based on extremal properties of r(φ) at φ = 0, π/m when n1 and n2 are in different intervals, and analyze how n1, n2 precisely affect the shapes of Gielis curves.

Abstract: We study the magnetic properties of platinum diselenide (PtSe2) intercalated with Ti, V, Cr, and Mn, using first-principle density functional theory (DFT) calculations and Monte Carlo (MC) simulations. First, we present the equilibrium position of intercalants in PtSe2 obtained from the DFT calculations. Next, we present the magnetic groundstates for each of the intercalants in PtSe2 along with their critical temperature. We show that Ti intercalants result in an in-plane AFM and out-of-plane FM groundstate, whereas Mn intercalant results in in-plane FM and out-of-plane AFM. V intercalants result in an FM groundstate both in the in-plane and the out-of-plane direction, whereas Cr results in an AFM groundstate both in the in-plane and the out-of-plane direction. We find a critical temperature of <0.01 K, 111 K, 133 K, and 68 K for Ti, V, Cr, and Mn intercalants at a 7.5% intercalation, respectively. In the presence of Pt vacancies, we obtain critical temperatures of 63 K, 32 K, 221 K, and 45 K for Ti, V, Cr, and Mn-intercalated PtSe2, respectively. We show that Pt vacancies can change the magnetic groundstate as well as the critical temperature of intercalated PtSe2, suggesting that the magnetic groundstate in intercalated PtSe2 can be controlled via defect engineering.

Abstract: The rational design of two-dimensional (2D) piezoelectric materials has recently garnered great interest due to their increasing use in technological applications, including sensor technology, actuating devices, energy harvesting, and medical applications. Several materials possessing high piezoelectric response have been reported so far, but a high-throughput first-principles approach to estimate the piezoelectric potential of layered materials has not been performed yet. In this study, we systematically investigated the piezoelectric (e(11), d(11)) and elastic (C-11 and C-12) properties of 128 thermodynamically stable 2D semiconductor materials by employing first-principle methods. Our high-throughput approach demonstrates that the materials containing Group-V elements produce significantly high piezoelectric strain constants, d(11) > 40 pm V-1, and 49 of the materials considered have the e(11) coefficient higher than MoS2 insomuch as BrSSb has one of the largest d(11) with a value of 373.0 pm V-1. Moreover, we established a simple empirical model in order to estimate the d(11) coefficients by utilizing the relative ionic motion in the unit cell and the polarizability of the individual elements in the compounds.

Abstract: The formation of metal oxalates in paintings has recently gained a great deal of interest within the field of heritage science as several types of oxalate compounds have been identified in oil paintings. The present work investigates the formation of metal oxalates in linseed oil in the presence of the artists' pigments zinc white, calcite, lead white, zinc yellow, chrome yellow, cadmium yellow, cobalt violet, and verdigris. The oil paint films were artificially photo-aged by exposure to UVA light at low and high relative humidity, and afterwards analysed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The results showed that, compared to the other pigments investigated, zinc white is especially prone to metal oxalate formation and that high humidity is a crucial factor in this process. Consequently, the reactivity and photo-aging of ZnO in various oil binding media was investigated further under simulated solar radiation and at high relative humidity levels. ATR-FTIR showed that zinc oxalate is formed in all oil binding media while X-ray powder diffraction (PXRD) revealed it was mainly present in an amorphous state. To examine whether atmospheric CO2(g) has any influence on the formation of zinc oxalate, experiments with isotopically enriched (CO2(g))-C-13 were performed. Based on ATR-FTIR measurements, neither (ZnC2O4)-C-13 nor (ZnCO3)-C-13 were formed which suggests that the carbon source for the oxalate formation is most likely the paint itself (and its oil component) and not the surrounding atmosphere.

Abstract: As part of the NWO Science4ArtsREVISRembrandtproject (2012-2018), novel chemical imaging techniques were developed and applied to the study of Rembrandt's late experimental painting technique (1651-1669). One of the unique features in his late paintings is his abundant use of smalt: a blue cobalt glass pigment that he often combined with organic lake pigments, earth pigments and blacks. Since most of these smalt-containing paints have discolored over time, we wanted to find out more about how these paintings may have originally looked, and what the role of smalt was in his paint. This paper reports on the use of smalt in complex pigment mixtures in Rembrandt'sHomer(1663), Mauritshuis, The Hague. Macroscopic X-ray fluorescence imaging (MA-XRF) assisted by computational analysis, in combination with SEM-EDX analysis of paint cross-sections, provides new information about the distribution and composition of the smalt paints in the painting. Paint reconstructions were carried out to investigate the effect of different percentages of smalt on the overall color, the drying properties, translucency and texture of the paint. Results show that the influence of (the originally blue) smalt on the intended color of the paint of theHomeris minimal. However, in mixtures with high percentages of smalt, or when combined with more transparent pigments, it was concluded that the smalt did produce a cooler and darker paint. It was also found that the admixture of opaque pigments reduced the translucent character of the smalt. The drying tests show that the paints with (cobalt-containing) smalt dried five times faster compared to those with glass (without cobalt). Most significantly, the texture of the paint was strongly influenced by adding smalt, creating a more irregular surface topography with clearly pronounced brushstrokes. Optical coherence tomography (OCT) was used as an additional tool to reveal differences in translucency and texture between the different paint reconstructions. In conclusion, this study confirmed earlier assumptions that Rembrandt used substantial amounts of smalt in his late paintings, not for its blue color, but to give volume and texture to his paints, to deepen their colors and to make them dry faster.

Abstract: Packed bed dielectric barrier discharge (PB-DBD) plasma reactors are very promising for various plasma catalysis applications, but the exact mechanisms of plasma-catalyst interaction are far from understood, because the plasma discharge and catalyst/packing properties are mutually dependent. To better understand the effect of packing dielectric material on the electrical plasma properties, we study here a single bead DBD plasma reactor operating in dry air, with beads of different dielectric constant and for different applied voltages, by means of fluid modelling validated by optical imaging experiments. Our study reveals that the plasma in the single bead DBD reactor can manifest itself in two different modalities, i.e. (a) polar discharges at the bead poles in contact with the electrodes, and (b) a streamer discharge caused by surface ionization waves, which bridges the gas gap. Beads with high dielectric constant result in localised electric field enhancement and hence yield a reduction of the applied voltage required for plasma production. At low applied voltage, the discharge appears as polar discharges between the bead and the electrodes, and upon higher voltage it undergoes a transition into a bridging streamer discharge. The transition voltage to the streamer mode rises for beads with higher dielectric constant. These observations are important for plasma catalysis applications. A higher dielectric constant yields a higher electric field and thus higher average electron energy and density, giving rise to more reactive species, but it also yields a confined discharge near the contact points of packing beads, limiting the interaction area between the catalyst and the active plasma species. In addition, our model reveals that the dielectric bead behaves as a capacitor and traps charges, which can explain the significant occurrence of partial discharging in PB-DBDs and non-parallelogram shaped Lissajous plots. Hence, equivalent circuit modelling of PB-DBDs should take into account the role of packing beads in charge trapping as a capacitor.