Modeling of catalytic coke formation in thermal cracking reactors

At the start-up period, the most important mechanism in the coke production with a clean reactor surface is the catalytic mechanism. The study of this mechanism can be very useful for the better comprehension of the coke production process. In this paper, a model was designed for such a production through the utilization of a catalytic mechanism and a kinetic model, capable of interpreting the catalytic coke production on the reactor surface. For the determination of the model reliability, the experimental data related to the naphtha feed, existing in literature, were used. In addition, the constant parameters of the model, the velocity and the activation energy constants, associated to the kinetic model, were calculated. The results of the developed model were in satisfactory agreement with the experimental data. Eventually, the catalytic coke amount in comparison with the total coke production on the reactor surface and its significance were under investigation.     

Synthesis and characterization of a novel nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-copoly[(styrene/acrylic acid)/grafted ethylene oxide and its application as a magnetic and recyclable phase-transfer catalyst in the preparation of β-azido alcohols and β-nitro alcohols

A facile method was developed for the synthesis of β-azido alcohols and β-nitro alcohols in the presence of a novel nano-Fe₃O₄-copoly[(styrene/acrylic acid)/grafted ethylene oxide (nano-Fe₃O₄-PS-Co-[PAA-g-PEG]) as a phase-transfer catalyst in water. The catalyst was characterized with IR, SEM, and TGA. This procedure offers several advantages, including excellent regioselectivity, high yields, short reaction times, a recyclable catalyst, easy separation of the catalyst through an external magnet, and easy workup.     

An improved second moment method for solution of pure advection problems

The second moment numerical method (SMM) of Egan and Mahoney [Numerical modeling of advection and diffusion of urban area source pollutant. Journal of Applied Meteorology 1972; 11 : 312–322] is adapted to solve for the pure advection transport equation in a variety of flow fields. SMM eliminates numerical diffusion by employing a procedure that takes into account the first and second moments of mass distribution in each grid element. For pure translational flow fields, the method is conservative, positive definite and shape‐preserving. In rotational and/or shear flows, the accuracy of SMM is significantly reduced. Two improvements are presented to make the SMM applicable to a wider range of flow problems. It is shown that the improved SMM (ISMM) is less diffusive and more shape‐preserving than the SMM in rotational and/or deformational flows. The ISMM can also be used to solve for a color function in compressible flow fields. The computational efficiency of this method is compared with that of other methods and, for a given accuracy, it is shown that ISMM is a cost‐effective, non‐diffusive and shape‐preserving method. Copyright © 2000 John Wiley & Sons, Ltd.     

Changing emission of divalent samarium doped into barium octoborate as a function of firing time

Barium octoborate has been synthesized by air firing of co-precipitated borates with additional boric acid. During the firing process, samarium ions doped into the matrix are reduced to the divalent state. Two different divalent samarium emission spectra have been observed from the material as a function of the firing history, even though the structure, as identified by powder X-ray diffraction remained consistent. A minor barium pentaborate impurity, in conjunction with significant thermal variability in the strength of the divalent samarium emission generated by the different sites in the two borate materials, appears to give rise to this phenomenon.     

Evaluation of spectral dispersion of optical constants of a-Se films from their normal-incidence transmittance spectra using Swanepoel algebraic envelope approach

Spectral dispersions of index of refraction \({n(\lambda )}\) and extinction coefficient \({\kappa (\lambda )}\) of undoped amorphous selenium (a-Se) films of three thicknesses (d?≈?0.5, 0.75, and 1.0 µm) were evaluated by analyzing experimental room-temperature normal-incidence transmittance-wavelength (\({{T_{{\text{exp}}}}(\lambda )} - \lambda\)) data (λ =?400–1100 µm) of their air-supported {a-Se film/thick glass slide}-stacks using Swanepoel’s transmission envelope theory of uniform films. Above a wavelength \({{\lambda _c}\,\, \approx \,\,640\;{\text{nm}}}\), as-measured \({{T_{{\text{exp}}}}(\lambda )}\,\, - \,\lambda\) spectra display well-resolved maxima and minima, with minor shrinkage in transparent and weak absorption regions (750–1100 nm). Below \({\lambda _{\text{c}}}\), a smeared sharp decline of \({{T_{{\text{exp}}}}(\lambda )}\) with decreasing λ, signifying strong absorption in a-Se films and existence of band-tail localized states. For λ > λ _c, the \({n\,(\lambda )}\, - \,\lambda\) data retrieved from algebraic envelope procedures followed a Sellmeier-like dispersion relation, with the best-fit values of high-frequency dielectric constant \({{\varepsilon _\infty }\, \approx \,\,{\text{4.9}}}\), static index of refraction \({{n_{\text{0}}} = n\left( {E\, \to \,{\text{0}}} \right)\,\, \approx \,\,{\text{2.43}}}\), and resonance wavelength \({{\lambda _0}\, \approx \,490\,\,{\text{nm}}}\), which may be assigned to onset of photogeneration in a-Se. Urbach-like dependency of absorption coefficient \({\alpha (h{{\nu }})}\) of a-Se films on photon energy \({h{{\nu }}}\) was realized with an Urbach-tail breadth of 85 meV. All achieved optical parameters were found to be slightly dependent on film thickness. Findings of present algebraic analysis are consistent with reported literature results obtained on the basis of other optical analytical approaches.     

MHD stagnation point flow towards a stretching sheet

The steady two-dimensional MHD stagnation point flow towards a stretching sheet with variable surface temperature is investigated. The governing system of partial differential equations are transformed into ordinary differential equations, which are then solved numerically using a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the flow field and heat transfer characteristics are obtained and discussed. It is found that the heat transfer rate at the surface increases with the magnetic parameter when the free stream velocity exceeds the stretching velocity, i.e. ε>1, and the opposite is observed when ε<1.     

A sulfonic acid functionalized ionic liquid as a homogeneous and recyclable catalyst for the one-pot synthesis of α-aminophosphonates

A sulfonic acid functionalized ionic liquid is used as a Brønsted acid catalyst for the one-pot, three-component synthesis of α-aminophosphonates from aldehydes and ketones at room temperature in water. This homogeneous catalytic procedure is simple and efficient and the catalyst can be reused at least six times without any noticeable decrease in catalytic activity.     

Spherical Kadomtsev-Petviashvili Solitons in a Suprathermal Complex Plasma

The nonlinear aspects of nonplanar dust acoustic (DA) solitary waves are investigated in an unmagnetized complex plasma comprising of cold dust grains, kappa-distributed ions as well as electrons. The nonplanar DA solitons are studied based on the reductive perturbation technique. It is shown that the evolution of DA solitons is governed by a spherical Kadomtsev-Petviashvili (sKP) equation and then the impact of suprathermality on the spatial structure as well as the nature of DA soliton is studied. It seems that the properties of DA solitons in nonplanar geometry are quite different from that of the planar solitons.     

Generalized vector variational-like inequalities and vector optimization

In this paper, we consider different kinds of generalized vector variational-like inequality problems and a vector optimization problem. We establish some relationships between the solutions of generalized Minty vector variational-like inequality problem and an efficient solution of a vector optimization problem. We define a perturbed generalized Stampacchia vector variational-like inequality problem and discuss its relation with generalized weak Minty vector variational-like inequality problem. We establish some existence results for solutions of our generalized vector variational-like inequality problems.     

Development,In-Vitro Characterization and Preclinical Evaluation of Esomeprazole-Encapsulated Proniosomal Formulation for the Enhancement of Anti-Ulcer Activity

Objective: The present study aimed to develop and optimize esomeprazole loaded proniosomes (EZL-PNs) to improve bioavailability and therapeutic efficacy. Method: EZL-PNs formulation was developed by slurry method and optimized by 33 box-Bhekhen statistical design software. Span 60 (surfactant), cholesterol, EZL concentration were taken as independent variables and their effects were evaluated on vesicle size (nm), entrapment efficiency (%, EE) and drug release (%, DR). Furthermore, optimized EZL-PNs (EZL-PNs-opt) formulation was evaluated for ex vivo permeation, pharmacokinetic and ulcer protection activity. Result: The EZL-PNs-opt formulation showed 616 ± 13.21 nm of vesicle size, and 81.21 ± 2.35% of EE. EZL-PNs-opt exhibited negative zeta potential and spherical confirmed scanning electron microscopy. EZL-PNs-opt showed sustained release of EZL (95.07 ± 2.10% in 12 h) than pure EZL dispersion. The ex-vivo gut permeation result exhibited a significantly (p < 0.05) enhanced flux than pure EZL. The in vivo results revealed 4.02-fold enhancement in bioavailability and 61.65% protection in ulcer than pure EZL dispersion (43.82%). Conclusion: Our findings revealed that EZL-PNs formulation could be an alternative delivery system of EZL to enhance oral bioavailability and antiulcer activity.