Comparison of RSM and ANN for the investigation of linear alkylbenzene synthesis over H14[NaP5W30O110]/SiO2 catalyst

Design of experiments (DOE) and artificial neural networks (ANNs) were successfully applied for studying the operating parameters of benzene alkylation with 1-decene over H₁₄[NaP₅W₃₀O₁₁₀]/SiO₂ catalyst. In this reaction catalyst loading, catalyst weight percent and benzene to 1-decene molar ratio (Bz/C₁₀) were chosen as independent variables in experimental design. Prediction of 1-decene conversion and 2-phenyldecane selectivity was performed applying response surface method (RSM) and ANN models. Final selected multi-layer (3-6-2-2) ANN model resulted a coefficient of determination (R²) of 0.95 for 1-decene conversion and 0.99 for 2-phenyldecane selectivity, while the R² of RSM was 0.93 and 0.92 for these two parameters.     

Temperature dependence of the dynamic electrical properties of Cu1+xMn1-xO2 (x = 0 and 0.06) crednerite materials

Polycrystalline samples of Cu_1+xMn_1-xO₂ (x?=?0 and 0.06) have been obtained by solid state reaction in silica tubes. Measurements of complex impedance (Z?=?Z′?+?iZ′′) at various temperatures T, between 30 °C and 120 °C and over the frequency range 100?Hz–2?MHz were performed. The frequency dependence of Z′′(f) exhibits a maximum which moves towards higher frequencies by increasing the temperature, proving thus the hopping of the charge carriers between the localized states is the dominant mechanism for the electrical conduction in the investigated samples. The barrier energy values were: 0.287?eV for CuMnO₂ and 0.208?eV for Cu_1.06Mn_0.94O₂.The conductivity spectrum, σ(f) follows the Jonscher universal law at each constant temperature. Based on the temperature and frequency dependencies of the electrical conductivity and using the variable-range-hopping (VRH) model, the frequency and temperature dependencies of the density of localized states near the Fermi level, N(E_F), the hopping distance, R and the hopping energy, W were computed. The results show that at constant frequency, N(E_F) does not depend on temperature for both samples. At constant temperature and frequencies up to 30?kHz, increasing the concentration of Cu ions leads to the decrease of R and W, whilst at high frequencies (over 100?kHz), R and W increase with the increase in the concentration of Cu ions.     

Analysis of the Fano in diamond

The Fano appears above a critical percolation threshold corresponding to the onset of the metallic conductivity on the boron impurity band. Its parameters are deduced from the fit of the Raman curves of heavily boron doped homoepitaxial diamond films. The large (10 cm⁻¹) widening and red shift of the phonon originates from its strong coupling with the continuum of electronic transitions. The strong deformation |q|≈2.2 of its Lorentzian shape is ascribed to the Raman cross-sections relatively large for the continuum of electronic interband transitions T_e and small for the phonon T_p whose negative value induces q<0.     

Energy efficiency of cogeneration systems

It is proposed to assess the energy efficiency of cogeneration systems in terms of the energy lost with the working fluid, Δq. This can be calculated either analytically or graphically using the equation Δq=(1?X)×V ₂ C ₂ T ₂/V ₁ C ₁ T ₁, whereX is the working-fluid recycle ratio;V ₁,C ₁, andT ₁ are the flow rate, heat capacity, and temperature of the working fluid at the entry to the reactor; andV ₂,C ₂, andT ₂ are the same variables at the exit from the reactor.     

Methane adsorption as a calorie upgrading PSA in the SNG process

A pressure swing adsorption (PSA) method for H₂N₂ removal is described in this paper. Results were achieved by selective adsorption of CH₄ and other hydrocarbons from the products of our demonstration plant (550 Nm³ h⁻¹) converting coke oven gas to substitute natural gas (SNG). High calorie gas (10 000 kcal Nm⁻³) was obtained from the pressure swing process between 0.26 and 4 kg cm⁻² after adsorption at 7 kg cm⁻². In the course of screening various adsorbents, a higher amount of methane adsorption, q_CH4, was obtained for higher q_N2. However, N₂ content was relatively low for the adsorbent of high q_CH4 due to the fact that the increase of q_CH4 was larger than that of q_N2. There were no such clear relations between q_H2 and q_CH4. N₂ content in the product from the zeolite adsorbent was relatively high. Therefore, active carbon was preferable to zeolite in this case. Although there was no correlation between q_CH4 and the total pore volume or BET surface area of the adsorbent, q_CH4 strongly depended upon the number of very small pores, e.g. below 8 Å diameter. Such an ultra small pore was quantified by applying the Horvath-Kawazoe isotherm in the low region of N₂ partial pressure between 0.00001 and 0.003 atm. As an application of this correlation, the optimal preparation conditions of the active carbon derived from coconut shell were established as temperature (900°C) versus time (20 min). This gave the highest performance of q_CH4 as 24.9 ml per ml-Ad among tested adsorbents.     

Surface fluctuations of polymer brushes probed by diffuse X-ray scattering

The diffuse scattering from the surfaces of melt and glassy polymer brushes has been studied systematically for the first time using polystyrene (PS) and poly(n-butylacrylate) (PnBA) brushes synthesized by free radical polymerization. The data show unambiguously that the diffuse scattering behavior varies systematically with brush thickness for both types of brushes. We attribute a cross-over in scattering with q_x, the in-plane scattering vector, to the presence of surface thermal fluctuations and their suppression for longer wavelengths, a phenomenon already reported for films of untethered chains. Long wavelength fluctuations are suppressed more strongly on the surface of a PS brush than on the surface of a film of untethered (‘free’) PS chains of comparable thickness, so that even in films of thickness, d, such that d/R_g>5 clear evidence of the suppression of fluctuations can still be seen in the experimentally available range of q_x. Fluctuations are suppressed for q_x less than a lower wavevector cut-off, q_l,c, which changes with film thickness, though much more weakly than for films of free chains. For values of d/R_g<4, where R_g is the unperturbed radius of gyration of a comparable free chain, q_l,c drops as d increases. For d/R_g>4 q_l,c begins to increase with brush thickness, in qualitative agreement with theory, indicative of a transition to a true ‘brush’ state in which stretching of the chains makes longer wavelength fluctuations at the surface unfavorable. Measurements with PnBA brushes having T_g substantially below room temperature confirm the trends mentioned above. Further, they give evidence that the value of q_l,c is temperature insensitive above T_g.     

On the estimation of the Kauzmann temperature from relaxation data

The well known WLF equation describing the relaxation behaviour of glass-forming liquids near the glass transition temperature has been rederived on the basis of Adam and Gibbs' excess entropy model, making use of a novel expression for the entropy of undercooled liquids. It has been shown that C₂ in the WLF equation is a nearly constant fraction of (T_s - T₂), where T_s and T₂ are the reference and the Kauzmann temperatures, respectively. It is demonstrated that the values of T₂ obtained from the relaxation data agree well with those calculated from thermodynamic data. The arguments used provide an explanation for the universality of the WLF constant, C₂.     

Optical anisotropy of a worm-like chain and its application to the determination of the persistence length in an aromatic polyamide

The optical anisotropy, as obtained from the depolarization of light scattering, has been evaluated for a worm-like chain as a function of the segment anisotropy δ₀ and of the ratio of the contour length L to the persistence length q. The comparison between the theoretical curves and the experimental data obtained for an aromatic polyamide [poly(para-phenylene terephthalamide)] in a range of DP from 7 to 30 leads to a value of q in good agreement with that calculated from other methods requiring a wider range of molecular weights.     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Exploration of N-Arylsulfonyl-indole-2-carboxamide Derivatives as Novel Fructose-1,6-bisphosphatase Inhibitors by Molecular Simulation

A series of N-arylsulfonyl-indole-2-carboxamide derivatives have been identified as potent fructose-1,6-bisphosphatase (FBPase) inhibitors (FBPIs) with excellent selectivity for the potential therapy of type II diabetes mellitus. To explore the structure–activity relationships (SARs) and the mechanisms of action of these FBPIs, a systematic computational study was performed in the present study, including three-dimensional quantitative structure–activity relationship (3D-QSAR) modeling, pharmacophore modeling, molecular dynamics (MD), and virtual screening. The constructed 3D-QSAR models exhibited good predictive ability with reasonable parameters using comparative molecular field analysis (q² = 0.709, R² = 0.979, r_pre² = 0.932) and comparative molecular similarity indices analysis (q² = 0.716, R² = 0.978, r_pre² = 0.890). Twelve hit compounds were obtained by virtual screening using the best pharmacophore model in combination with molecular dockings. Three compounds with relatively higher docking scores and better ADME properties were then selected for further studies by docking and MD analyses. The docking results revealed that the amino acid residues Met18, Gly21, Gly26, Leu30, and Thr31 at the binding site were of great importance for the effective bindings of these FBPIs. The MD results indicated that the screened compounds VS01 and VS02 could bind with FBPase stably as its cognate ligand in dynamic conditions. This work identified several potential FBPIs by modeling studies and might provide important insights into developing novel FBPIs.     

Effect of structure on the glass transition temperatures of linear and crosslinked poly(isobornylacrylate-co-isobutylacrylate)

A series of linear acrylic copolymers based on Isobornyl acrylate (IBOA) and isobutyl acrylate (IsoBA) were elaborated by radical photopolymerization. In addition, several photochemically crosslinked poly(IBOA-co-IsoBA) were prepared by introducing small amounts of 1,6-hexanedioldiacrylate as crosslinking agent. The evolution of the glass transition temperature was determined experimentally by differential scanning calorimetry as a function of composition for both linear and crosslinked poly(IBOA-co-IsoBA), yielding T_g values ranging from (~249) to (~315 K). Theoretical modeling was performed applying Fox, Gordon-Taylor and Couchman-Karasz models by simple calculations using experimental data, leading to only fair agreement between theoretical and experimental values, or by applying fitting procedures involving one or two adjustable parameters. Likewise, the Kwei model, known to take into account hydrogen bonding interactions between monomers, could not describe well the evolution of T_g, indicating the existence of other factors influencing T_g. Finally, a thermodynamic approach based on entropy considerations allowed to attribute an explanation of the evolution of T_g.     

Influence of alternating sequential fraction on the melting and glass transition temperatures of ethylene-tetrafluoroethylene copolymer

The melting (T_m) and glass transition (T_g) temperatures of a series of ethylene (E)-tetrafluoroethylene (TFE) copolymer (ETFE) have been found to show unique dependence on the TFE content with the minimal and maximal points. These behaviors have been interpreted successfully on the basis of the degree of alternation of E and TFE monomeric units along the skeletal chain. The melting point of a perfectly alternating copolymer is estimated to be 295 °C on the basis of the dependence of T_m using a modified Flory’s equation. The corresponding T_g was estimated as 145 °C by applying a modified Gibbs-Damnation’s equation.     

Miscibility with positive deviation in Tg-composition relationship in blends of poly(2-vinyl pyridine)-block-poly(ethylene oxide) and poly(p-vinyl phenol)

Phase behavior and miscibility with positive deviation from linear T_g-composition relationship in a copolymer/homopolymer blend system, poly(2-vinyl pyridine)-block-poly(ethylene oxide) (P2VP-b-PEO)/poly(p-vinyl phenol) (PVPh), were investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR), optical microscopy (OM), and scanning electron microscopy (SEM). Optical and electron microscopy results as well as NMR proton spin-lattice relaxation times in laboratory frame () all confirmed the miscibility as judged by the T_g criterion using DSC. In comparison to the literature result on a homopolymer/homopolymer blend of P2VP/PVPh, fitting with the Kwei equation on the T_g-composition relationship for the block-copolymer/homopolymer blend of P2VP-b-PEO/PVPh blend system yielded a smaller q value (q = 120) for P2VP-b-PEO/PVPh than that for P2VP/PVPh blend (q = 160). The FT-IR and ¹³C NMR results revealed hydrogen-bonding interactions between the pendant pyridine group of P2VP-b-PEO and phenol unit in PVPh, which is responsible for the noted positive deviation of the T_g-composition relationship. Comparison of the shifts of hydroxyl IR absorbance band, reflecting the average strength of H-bonding, indicates a decreasing order of P2VP/PVPh > P2VP-b-PEO/PVPh > PEO/PVPh blends. The PEO block in the copolymer segment tends to defray the interaction strength in the P2VP-b-PEO/PVPh blends because of relative weaker interaction between PEO and PVPh than that between P2VP and PVPh pairs. A comparative ternary (P2VP/PEO)/PVPh blend was also studied as the controlling experiments for comparison to the P2VP-b-PEO/PVPh blend. The thermal behavior and interaction strength in (P2VP/PEO)/PVPh ternary blends are discussed with those in the P2VP-b-PEO/PVPh copolymer/homopolymer blend.     

The Study of Dynamic Potentials of Highly Excited Vibrational States of DCP: From Case Analysis to Comparative Study with HCP

The dynamic potentials of highly excited vibrational states of deuterated phosphaethyne (DCP) in the D–C and C–P stretching coordinates with anharmonicity and Fermi coupling are studied in this article and the results show that the D-C-P bending vibration mode has weak effects on D–C and C–P stretching modes under different Polyad numbers (P number). Furthermore, the dynamic potentials and the corresponding phase space trajectories of DCP are given, as an example, in the case of P = 30. In the end, a comparative study between deuterated phosphaethyne (DCP) and phosphaethyne (HCP) with dynamic potential is done, and it is elucidated that the uncoupled mode makes the original horizontal reversed symmetry breaking between the dynamic potential of HCP (q₃) and DCP (q₁), but has little effect on the vertical reversed symmetry, between the dynamic potential of HCP (q₂) and DCP (q₃).     

Polyether-metal salt complexes: 1. The elevation of the glass transition temperature of polyethers by metal salts

Various metal halides have been dispersed in high and low molecular weight, amorphous poly(propylene oxide), by solution blending techniques, to give single phase polymeric complexes which remained thermoplastic even at very high salt loadings. These complexes were amorphous and showed a single well-defined glass transition temperature (T_g) by differential thermal analysis with the T_g of the complex up to 140°C greater than the T_g of the parent polymer. The T_g elevation depended upon both the amount and the type of salt added and for a given salt the elevation followed a sigmoidal curve which levelled out at high salt concentrations. The T_g data have been interpreted in terms of a chelate ring model involving the co-ordination of two adjacent ether oxygen atoms in the polymer backbone to the salt. Using this model it was possible to consider the complex as a random copolymer consisting of complexed and uncomplexed monomer units. The contribution of crosslinking by metal salts to the elevation of T_g was assessed by studying poly(tetramethylene glycol)-zinc chloride complexes in which chelate formation is entropically unfavourable. Mechanical data are reported for ZnCl₂ complexes with high molecular weight poly(propylene oxide). The results indicate that ZnCl₂ increased the rubbery modulus and this has been interpreted in terms of ZnCl₂ forming a few, weak intermolecular crosslinks.     

Enhanced room temperature ammonia response of 2D-Ti3C2Tx MXene decorated with Ni(OH)2 nanoparticles

Due to the expansion of human production activities, toxic ammonia (NH₃) is excessively released into the atmosphere, being a huge threat to human health and the natural environment. Therefore, it is of great significance to design an easy-synthesized gas-sensing material with both good room temperature sensitivity and selectivity for trace-level NH₃ detection. Herein, we fabricate a chemiresistive NH₃ gas sensor with enhanced performance based on Ni(OH)₂/Ti₃C₂T_x hybrid materials. The Ni(OH)₂/Ti₃C₂T_x hybrid materials are synthesized by an in-situ electrostatic self-assembly method. Attributed to the formation of interfacial heterojunctions and the modulation of carrier density, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor exhibits high response, outstanding repeatability, good selectivity and stability in low concentrations of NH₃. Moreover, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor has a higher response to 10 ppm NH₃ at the relative humidity of 40% and 60%, which makes it promising for applications in real complex environments with high humidity. Benefitting from the low power consumption and easy fabrication process, the Ni(OH)₂/Ti₃C₂T_x hybrid sensor possesses a broad application prospect in the internet of things (IoT) environmental monitoring.     

Structural,magnetic and dielectric properties of the novel magnetic spinel compounds ZnCoSnO4 and ZnCoTiO4

The transparent semiconductor Zn₂SnO₄ with cubic spinel structure and the isostructural Zn₂TiO₄ have been magnetically doped with Co²⁺. ZnCoSnO₄ and ZnCoTiO₄ exhibit ferrimagnetism below T_N ≈ 13?K and T_N ≈ 17?K. Ferrimagnetic moments are evident in M vs H curves below T_N by small hysteresis. Fits to strictly linear Curie-Weiss plots above T_N give μ_eff ≈ 4.86 μ_B and ≈4.91 μ_B for ZnCoSnO₄ and ZnCoTiO₄, above theoretical predictions. Impedance spectroscopy data from sintered ceramic can be fitted with a standard equivalent circuit model based on two RC elements for bulk and GB areas. The relative dielectric permittivity of the bulk is ≈20 and ≈30 for Zn₂SnO₄ and Zn₂TiO₄. The semiconducting ZnCoSnO₄ and ZnCoTiO₄ceramics exhibit bulk resistivity of ≈1 10⁶?Ω?cm and ≈1 10⁵?Ω?cm at 560?K (287?°C), and bulk activation energies of E_A ≈ 1.2?eV and 1.1?eV.     

N.m.r. study of the ferroelectric phase transition in a 7030mol% copolymer of vinylidene fluoride (VF2) and trifluoroethylene (TrFE)

Nuclear magnetic resonance (n.m.r.) studies of ¹⁹F nuclei in a $\text{70}\text{30}\text{mol}\text{\%}$ random copolymer of vinylidene fluoride and trifluoroethylene were performed at 9.14 MHz and 20.0 MHz. The free induction decays (FIDs) were analysed in terms of two T₂ components attributed to the amorphous and crystalline portions of the polymer. The changes in crystallinity as well as the effects of the ferroelectric transition were observed during cycles of heating and cooling between 20°C and 140°C. The crystalline component of the FID lengthens by a factor of 2 at 100°C on heating and decreases by this factor at 60°C on cooling, thus exhibiting the thermal hysteresis of this ferroelectric transition. The spin-lattice relaxation was also investigated. From measurements at 9.14 MHz the observed longitudinal relaxation time T₁ appears to be dominated by the dynamics of the amorphous phase and exhibits no anomaly through the phase transition. However, from measurements at 20 MHz, well defined minima of T₁ were observed, which are associated with the ferroelectric transition (especially after repeated annealing of the samples). Results are discussed in terms of the crystalline phase structure, which appears dynamically disordered above the ferroelectric phase transition. An analogy is considered with the plastic phase transitions encountered in molecular crystals.     

Modeling the selectivity of activated carbons for efficient separation of hydrogen and carbon dioxide

Grand canonical Monte Carlo simulations (GCMC) are carried out to investigate the separation of hydrogen and carbon dioxide via adsorption in activated carbons. In the simulations, both hydrogen and carbon dioxide molecules are modeled as Lennard-Jones spheres, and the activated carbons are represented by a slit-pore model. At elevated temperatures (T = 505 and 923 K), the activated carbons exhibit essentially no preference over the two gases and the selectivity of carbon dioxide relative to hydrogen falls monotonically as the pore size increases. At room temperature, however, the selectivity of carbon dioxide relative to hydrogen reaches up to 90, indicating that hydrogen and carbon dioxide can be efficiently separated. Furthermore, the optimized pore sizes, of width H = 1.48 nm for the bulk mole fraction ratio of x_CO2/x_H2=1:2 and H = 1.18 nm for x_CO2/x_H2=1:8, are identified in which the activated carbons show the highest selectivity for the separation of hydrogen and carbon dioxide.     

Dynamics of thermoresponsive PNIPAM-g-PEO copolymer chains in semi-dilute solution

The effects of concentration and temperature on dynamics of poly(N-isopropylacrylamide)-graft-poly(ethylene oxide) (PNIPAM-g-PEO) chains in semi-dilute aqueous solution were studied by static and dynamic laser light scattering. The intensity-intensity time correlation function shows a fast and a slow relaxation mode, with line widths Γ_f and Γ_s, respectively. Γ_f is scaled to the scattering vector (q) as Γ_f ∝ q², revealing that it is due to the cooperative diffusion of the subchains between two neighboring entangled points. As the concentration increases, the slow relaxation becomes slower and contributes more to the total scattered light intensity, indicating that the slow relaxation is related to the chain entanglement. On the other hand, when the solution temperature increases, the PNIPAM chain backbone shrinks, but the fast relaxation remains and the slow mode slows down with a minimum rate at ∼33 °C. It indicates that the slow mode arises from inter-chain clustering, which is gradually suppressed by the intra-chain shrinking. The sample position independence of the time-averaged scattered light intensity 〈I〉_T reveals that the solution is homogeneous and the clustering is transient.