Insight into Heterogeneity Effects in Methane Hydrate Dissociation via Pore-Scale Modeling

A large number (1253) of high-quality streaming potential coefficient (\(C_\mathrm{sp})\) measurements have been carried out on Berea, Boise, Fontainebleau, and Lochaline sandstones (the latter two including both detrital and authigenic overgrowth forms), as a function of pore fluid salinity (\(C_\mathrm{f})\) and rock microstructure. All samples were saturated with fully equilibrated aqueous solutions of NaCl (10\(^{-5}\) and 4.5 mol/dm\(^{3})\) upon which accurate measurements of their electrical conductivity and pH were taken. These \(C_\mathrm{sp}\) measurements represent about a fivefold increase in streaming potential data available in the literature, are consistent with the pre-existing 266 measurements, and have lower experimental uncertainties. The \(C_\mathrm{sp}\) measurements follow a pH-sensitive power law behaviour with respect to \(C_\mathrm{f}\) at medium salinities (\(C_\mathrm{sp} =-\,1.44\times 10^{-9} C_\mathrm{f}^{-\,1.127} \), units: V/Pa and mol/dm\(^{3})\) and show the effect of rock microstructure on the low salinity \(C_\mathrm{sp}\) clearly, producing a smaller decrease in \(C_\mathrm{sp}\) per decade reduction in \(C_\mathrm{f}\) for samples with (i) lower porosity, (ii) larger cementation exponents, (iii) smaller grain sizes (and hence pore and pore throat sizes), and (iv) larger surface conduction. The \(C_\mathrm{sp}\) measurements include 313 made at \(C_\mathrm{f} > 1\) mol/dm\(^{3}\), which confirm the limiting high salinity \(C_\mathrm{sp}\) behaviour noted by Vinogradov et al., which has been ascribed to the attainment of maximum charge density in the electrical double layer occurring when the Debye length approximates to the size of the hydrated metal ion. The zeta potential (\(\zeta \)) was calculated from each \(C_\mathrm{sp}\) measurement. It was found that \(\zeta \) is highly sensitive to pH but not sensitive to rock microstructure. It exhibits a pH-dependent logarithmic behaviour with respect to \(C_\mathrm{f}\) at low to medium salinities (\(\zeta =0.01133 \log _{10} \left( {C_\mathrm{f} } \right) +0.003505\), units: V and mol/dm\(^{3})\) and a limiting zeta potential (zeta potential offset) at high salinities of \({\zeta }_\mathrm{o} = -\,17.36\pm 5.11\) mV in the pH range 6–8, which is also pH dependent. The sensitivity of both \(C_\mathrm{sp}\) and \(\zeta \) to pH and of \(C_\mathrm{sp}\) to rock microstructure indicates that \(C_\mathrm{sp}\) and \(\zeta \) measurements can only be interpreted together with accurate and equilibrated measurements of pore fluid conductivity and pH and supporting microstructural and surface conduction measurements for each sample.     

The effect of static external magnetic field on the nonlinear absorption of the S-polarised short laser pulse in collisional underdense plasma

A new, user-friendly, linear plasma device has been developed in our laboratory where a quiescent (\(\Delta n/n \approx 1\%\)), low temperature (1–10 eV), pulsed (3–10 ms) plasma can be produced over a large uniform region of 30–40 cm diameter and 40 cm length. Salient features of the device include the flexibility of tuning the plasma density in the range of \(10^{10}\) to \(10^{12}\,\hbox {cm}^{-3}\) and capability of scanning the plasma and field parameters in two dimensions with a precision of < 1 mm. The plasma is produced by a multifilamentary cathode and external magnetic field by Helmholtz coils, both designed and constructed in-house. The plasma parameters can be measured by Langmuir probes and electromagnetic field parameters by miniature magnetic probes and Rogowski coils. The plasma produced is uniform and essentially unbounded for performing experiments on waves and turbulence. The whole device can be operated single-handedly by undergraduate or graduate students. The device can be opened, serviced, new antennas/probes installed and ready for operation in a matter of hours. Some results on the excitation of electromagnetic structures in the context of electron magnetohydrodynamics (EMHD) are also presented to demonstrate the suitability of the device for carrying out such experiments.     

Molecular Modeling of Human CCR2 Receptor within POPC Lipid Bilayer

Structural Chemistry - Chemokine receptor 2 (CCR2), a G-protein coupled receptor (GPCR), is a critical target for several inflammatory and autoimmune diseases. The main restriction on designing...     

Heat-resistant, pyridine-based polyamides containing ether and ester units with improved solubility

<正>A diamine containing ether and ester units,as basic monomer for the preparation of polyamides,was prepared via three consecutive reactions.Nucleophilic substitution reaction of 1,4-dihydroxy benzene with 4-nitrobenzoyl chloride produced 4-hydroxyphenyl 4-nitrobenzoate(HPNB).Reduction of nitro groups to amino groups using Fe and HC1 resulted in preparation of 4-hydroxyphenyl 4-aminobenzoate(HPAB).The diamine was synthesized through nucleophilic substitution reaction of HPAB with 2,6-dichloropyridine The precursors and diamine were fully characterized by common methods,and the diamine was polycondensed with different diacid chlorides in the presence of an acid scavenger to prepare new polyamides.The polyamides were characterized,and their physical properties including thermal stability and behavior, inherent viscosity and solubility were studied.     

Entanglement generation by electric field background

The quantum vacuum is unstable under the influence of an external electric field and decays into pairs of charged particles, a process which is known as the Schwinger pair production. We propose and demonstrate that this electric field can generate entanglement. Using the Schwinger pair production for constant and pulsed electric fields, we study entanglement for scalar particles with zero spins and Dirac fermions. One can observe the variation of the entanglement produced for bosonic and fermionic modes with respect to different parameters.     

Synthesis and characterization of polypyrrole/Sn-doped TiO2 nanocomposites (NCs) as a protective pigment

We have chemically polymerized pyrrole in the presence of Sn-doped TiO₂ nanoparticles (NPs) and TiO₂ (NPs) which act as a protective pigment. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) results show a core-shell structure of pigments in which TiO₂ and Sn-doped TiO₂ NPs have a nucleus effect and caused a homogenous PPy core-shell type morphology leading to coverage of the TiO₂ and Sn-doped TiO₂ NPs by PPy deposit. The XRD results indicate that the crystalline size of polypyrrole/TiO₂ NCs and polypyrrole/Sn-doped TiO₂ NCs were approximately 93.46 ± 0.06 and 23.36 ± 0.06 nm respectively. The electrochemical impedance spectroscopy (EIS) results show that the performance of polypyrrole/Sn-doped TiO₂ NCs is better than polypyrrole/TiO₂ NCs. The results indicate that increasing the area of synthesized polypyrrole in the presence of Sn-doped TiO₂ NPs can increase its ability to interact with the ions liberated during the corrosion reaction of steel in the presence of NaCl. The UV-vis results show that the band gap of TiO₂ NPs increases with doped of Sn in lattice of TiO₂. The increase of the band gap of TiO₂ with doping of Sn can decrease the charge transfer through the coating.     

The Effect of Aminated Carbon Nanotube and Phosphorus Pentoxide on the Thermal Stability and Flame Retardant Properties of the Acrylonitrile–Butadiene–Styrene

Multi-walled carbon nanotubes (MWCNT) have been successfully functionalized with amino groups. In order to improve the thermal stability of the polymer nanocomposite, aminated-MWCNTs were added to acrylonitrile–butadiene–styrene (ABS). The influence of MWCNT and phosphorus pentoxide nanostructures on the flame retardancy of the ABS matrix was studied using UL-94 test. The results show that the MWCNT nanostructure can’t enhance the flame retardancy of the ABS matrix but synergism of MWCNT and P₂O₅ can effectively improve the flame retardancy of the nanocomposite.     

Preconcentration and determination of ceftazidime in real samples using dispersive liquid–liquid microextraction and high‐performance liquid chromatography with the aid of experimental design

A rapid and simple method for the extraction and preconcentration of ceftazidime in aqueous samples has been developed using dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography analysis. The extraction parameters, such as the volume of extraction solvent and disperser solvent, salt effect, sample volume, centrifuge rate, centrifuge time, extraction time, and temperature in the dispersive liquid–liquid microextraction process, were studied and optimized with the experimental design methods. Firstly, for the preliminary screening of the parameters the taguchi design was used and then, the fractional factorial design was used for significant factors optimization. At the optimum conditions, the calibration curves for ceftazidime indicated good linearity over the range of 0.001–10 μg/mL with correlation coefficients higher than the 0.98, and the limits of detection were 0.13 and 0.17 ng/mL, for water and urine samples, respectively. The proposed method successfully employed to determine ceftazidime in water and urine samples and good agreement between the experimental data and predictive values has been achieved.     

Nano structures of group 13-15 mixed heptamer clusters: a computational study

The structural and thermodynamic characteristics of lowest-energy structures of group 13-15 mixed heptamers in two distinct series [(HM)(k)(HM')(l)(NH)(7)] (M, M' = B, Al, Ga and k + l = 7) and [(HGa)(7)(YH)(m)(Y'H)(n)] (Y,Y' = N, P, As and m + n = 7) have been systematically investigated using the density functional approach. Our main goal is to get knowledge of the preferential bonding patterns of the first three rows of group 13-15 elements for the construction of mixed heptameric clusters. Structural parameters, thermodynamic properties of oligomerization reaction, band gaps, and dipole moments of the 18 lowest-energy structures of the studied heptamers in each series are compared to their corresponding binary parents, that is, [(HM)(7)(NH)(7)] and [(HGa)(7)(YH)(7)]. The stability of different isomer structures is discussed to reveal the competitiveness of group 13 and 15 bonding. Mixed heptamers are predicted to be thermodynamically more stable compared to a mixture of monomers. However, the favorability for the generation of mixed heptamers strongly depends on the nature of inserted metal and nonmetal pairs of group 13-15. Moreover, it is found that among all studied heptamers the smaller band gaps correspond to arsenic containing species which are close to the semiconducting regime, around 4.62-4.98 eV.     

Topological Soliton and Other Exact Solutions to KdV–Caudrey–Dodd–Gibbon Equation

This paper studies the KdV–Caudrey–Dodd–Gibbon equation. The modified F-expansion method, exp-function method as well as the G′/G method are used to extract a few exact solutions to this equation. Later, the ansatz method is used to obtain the topological 1-soliton solution to this equation. The constraint conditions are also obtained that must remain valid for the existence of these solutions.