Chelates and corrosion inhibition of newly synthesized Schiff bases derived from <Emphasis Type="Italic">o</Emphasis>-tolidine

New copper(II), nickel(II), iron(III) and palladium(II) Schiff base complexes derived from o-tolidine and selected aldehydes, namely salicyaldehyde and 2-hydroxynaphthaldehyde have been synthesized and characterized by a combination of elemental analyses, magnetic moments, spectral (u.v.–vis., i.r.) and thermal (tg, dtg) mesurements. The corrosion inhibition of aluminium and copper in 1 M HCl and chromium–nickel steel in crude oil using N,N′bis(salicyledene)-o-tolidine have been studied by weight loss method.     

Synthesis of ethyl cis 2-[(Diethoxyphosphoryl)methyl]-7-oxo-3-phenyl-6-phthalimido-l-azabicyclo[3.2.0]hept-3-ene-2-carboxylate and Methyl cis-2-Bromo-3-methyl-8-oxo-7-phthalimido-4-oxa-1-azabicyclo[4.2.0]octane-2-carboxylate

The synthesis of a Δ¹-carbapenem and two β-lactams possessing a Br-atom at the N-substituting center not involved in the lactam ring and bearing the carboxyl group is described. The β-lactams having this kind of Br-substitution are more susceptible to nucleophilic attack than those having a conjugated double bond with the N-atom of the β-lactam ring. DBU is found to be an excellent reagent for the elimination of the silyloxy function. Moreover, a simple method for the addition of diethyl phosphite to an α, β-unsaturated double bond using a catalytic amount of NaH is described.     

Spectral Analysis of Some Distillates from Asphalt Cracking and Evaluation of UTIMAC as Cracking Catalyst

This paper demonstrates the spectral analysis of some distillates obtained from asphalt cracking in the presence of a conventional expensive catalyst, i.e., HZSM‐5, and local cheap and readily available clay, i.e., UTIMAC. Each distillate was fractionated into pentane soluble (PI) and pentane insoluble (PI) fractions based on solubility in n, pentane. Both PS and PI obtained in the case of HZSM‐5 and UTIMAC were analyzed by ¹H‐NMR spectrophotometry using CDCl₃ as dissolving solvent and tetramethylsilane (TMS) as internal standard. It is evident from the profiles that both catalysts caused the generation of some peaks ascribed to methylene and methene configurations in the aliphatic region. Bands corresponding to aromatic configurations were also generated. The results indicate that the cheap local catalyst used has comparable suitability with the conventional expensive catalyst in terms of asphalt cracking.     

Solubility of polycyclic aromatics in binary solvent mixtures using activity coefficient models

Polycyclic aromatic hydrocarbons (PAHs) precipitation is one of the major problems in the hydrocracking units. In this investigation, pyrene and phenanthrene were selected because they were found to be in higher concentrations in the feed to hydrocracking units. Their solubilities were investigated in toluene solvent mixture of iso-octane and heptane over a temperature range from 293 to 323 K. The experimental solubility data were used to predict the interaction parameters for seven different solid–liquid equilibrium models. The following activity coefficient models were used; Wilson, NIBS/Redlich–Kister, UNIQUAC, modified UNIFAC, modified UNIFAC (Dortmund), Flory–Huggins and Sheng. The interaction parameters were expressed as a second-order polynomial function in temperature. In order to test the models, the average absolute deviation percentage (AADP) was used. The overall AADP was found to range from approximately 7 to 14%. The models can be arranged according to their accuracy in a descending order based on AADP as follows: NIBS/Redlich–Kister, Wilson, UNIQUAC, Sheng, Flory–Huggins, modified UNIFAC (Dortmund) and finally modified UNIFAC. All models used in this work gave reasonable results; however, the group contribution models can also be used as a predictive tool for the solubility measurement of pyrene and phenanthrene in other solvents containing the same groups of the solvents used in this study.     

Nonlinear Galerkin methods and mixed finite elements: two-grid algorithms for the Navier-Stokes equations

Summary. A nonlinear Galerkin method using mixed finite elements is presented for the two-dimensional incompressible Navier-Stokes equations. The scheme is based on two finite element spaces and for the approximation of the velocity, defined respectively on one coarse grid with grid size and one fine grid with grid size and one finite element space for the approximation of the pressure. Nonlinearity and time dependence are both treated on the coarse space. We prove that the difference between the new nonlinear Galerkin method and the standard Galerkin solution is of the order of $H^2$, both in velocity ( and pressure norm). We also discuss a penalized version of our algorithm which enjoys similar properties. Received October 5, 1993 / Revised version received November 29, 1993     

2D water layer enclathrated between Mn(II)-Ni(CN)4 coordination frameworks

A [Ni(CN)₄]²⁻-based two-dimensional Mn(II) coordination polymer {Mn(H₂O)₂[NiCN]₄·4H₂O}, in which the coordination layers are stacked on top of each other sandwiching 2D water layer of boat-shaped hexagonal water clusters has been synthesized. The complex exhibits high thermal decomposition temperature and reversible water absorption, which were clearly demonstrated by thermal and PXRD studies on the parent and rehydrated complex after dehydration.     

Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas

Strong intensity enhancement or extinction of some single harmonics is observed in high-harmonic generation from 48 fs Ti:sapphire laser pulses propagating through preformed low-excited laser-produced plasmas of various materials (GaAs, Cr, InSb, stainless steel). The intensities of some of the harmonics in the mid- and end-plateau regions vary from ~23-fold enhancement to near disappearance compared with those of the neighboring ones. It is also shown that the observed intensity enhancement (or extinction) can be varied by controlling the chirp of the driving laser radiation.     

Prediction of flow stress at hot working condition

A mathematical model has been developed to determine flow stress at hot deformation condition. The proposed model is capable of including work softening due to dynamic phase transformations as well as the effect of temperature and strain rate variation on flow stress utilizing the additivity rule for strain. To verify the model, hot compression tests for two grades of steels has been carried out. The comparison between the experimental and theoretical results confirms the validity of the model.     

Delay equations with fluctuating delay related to the regenerative chatter

The mathematical models representing machine tool chatter dynamics have been cast as differential equations with delay. In this paper, non-linear delay differential equations with periodic delays which model the machine tool chatter with continuously modulated spindle speed are studied. The explicit time-dependent delay terms, due to spindle speed modulation, are replaced by state-dependent delay terms by augmenting the original equations. The augmented system of equations is autonomous and has two pairs of pure imaginary eigenvalues without resonance. The reduced bifurcation equation is obtained by making use of Lyapunov-Schmidt Reduction method. By using the reduced bifurcation equations, the periodic solutions are determined to analyze the tool motion. Analytical results show both modest increase of stability and existence of periodic solutions near the new stability boundary.