Polarization orthogonalization properties of optical systems

We investigate the conditions under which an optical system (or device) may transform polarization states at its input into orthogonal states at its output. We find that such polarization orthogonalization is possible if the Jones matrix of the optical system satisfies a specific inequality. One, two, or an infinite number of input polarization states may be orthogonalized. In the latter case, the locus of input states is a circle in the complex plane (and on the Poincaré sphere) of polarization. Several examples are given for illustration.     

Determination of the binding constants of modafinil enantiomers with sulfated β‐cyclodextrin chiral selector by capillary electrophoresis using three different linear plotting methods

Binding constants for the enantiomers of modafinil with the negatively charged chiral selector sulfated‐β‐CD (S‐β‐CD) using CE technique is presented. The calculations of the binding constants employing three different linearization plots (double reciprocal, X‐reciprocal and Y‐reciprocal) were performed from the electrophoretic mobility values of modafinil enantiomers at different concentrations of S‐β‐CD in the BGE. The highest inclusion affinity of the modafinil enantiomers were observed for the S‐enantiomer–S‐β‐CD complex, in agreement with the computational calculations performed previously. Binding constants for each enantiomer–S‐β‐CD complex at different temperatures, as well as thermodynamic parameters for binding, were calculated. Host–guest binding constants using the double reciprocal fit showed better linearity (r²>0.99) at all temperatures studied (15–30°C) and compared with the other two fit methods. The linear van't Hoff (15–30°C) plot obtained indicated that the thermodynamic parameters of complexation were temperature dependent for the enantiomers.     

Temperature-induced phase transition; Polymorphism in BP2 SAMs on Au(111)

Self-assembled monolayers (SAMs) of ω-(4′-methylbiphenyl-4-yl)ethanethiol (CH₃(C₆H₄)₂(CH₂)₂SH, BP2) prepared at different temperatures on Au(111) substrates were investigated using scanning tunneling microscopy (STM). Also, the effect of the incubation time of the gold substrate in the thiol solution was examined. The STM results showed that samples prepared at room temperature were significantly different from those prepared at elevated temperatures in their surface morphology, space group and size of unit cell. The micrographs of samples prepared at higher temperatures revealed a pronounced and progressive increase in the size of the well-known etch-pits at the expense of their density with increasing preparation temperature (but the increase did not continue for SAMs prepared at 348 K). The average domain size was found to increase significantly with increasing preparation temperature. In addition, polymorphism was observed in BP2 SAMs at all investigated temperatures. This study has demonstrated that solution temperature and incubation time are key factors controlling the two-dimensional SAM structure of BP2 molecules.      

Enantioselective analysis of ofloxacin and ornidazole in pharmaceutical formulations by capillary electrophoresis using single chiral selector and computational calculation of their inclusion complexes

A capillary electrophoretic method for the separation of the enantiomers of both ofloxacin and ornidazole is described. Several parameters affecting the separation were studied, including the type and concentration of chiral selector, buffer pH, voltage and temperature. Good chiral separation of the racemic mixtures was achieved in less than 16 min with resolution factors Rs = 5.45 and 6.28 for ofloxacin and ornidazole enantiomers, respectively. Separation was conducted using a bare fused-silica capillary and a background electrolyte (BGE) of 50 mM H₃PO₄-1 M tris solution; pH 1.85; containing 30 mg mL⁻¹ of sulfated-β-cyclodextrin (S-β-CD). The separation was carried out in reversed polarity mode at 25 °C, 18 kV, detection wavelength at 230 nm and using hydrodynamic injection for 15 s. Acceptable validation criteria for selectivity, linearity, precision, and accuracy were studied. The limits of detection (LOD) and limits of quantitation (LOQ) of the enantiomers (ofloxacin enantiomer 1 (OF-E1), ofloxacin enantiomer 2 (OF-E2), ornidazole enantiomer 1 (OR-E1) and ornidazole enantiomer 2 (OR-E2)) were (0.52, 0.46, 0.54, 0.89) and (1.59, 1.40, 3.07, 2.70) μg mL⁻¹, respectively. The proposed method was successfully applied to the assay of enantiomers of both ofloxacin and ornidazole in pharmaceutical formulations. The computational calculations for the enantiomeric inclusion complexes rationalized the reasons for the different migration times between the ofloxacin and ornidazole enantiomers.     

The Utilization of Electrokinetics in Geotechnical and Environmental Engineering

Electrokinetics can be utilized to solve many problems in geotechnical and environmental engineering. The processes which occur in association with electrokinetics are complicated and difficult to control. The success of the application depends on certain conditions which are controlled by many parameters. It is therefore important to understand these processes so that methods and procedures can be optimized. In this paper theoretical considerations, results of tests and examples of in situ applications are presented and discussed. The presented examples show ways of controlling and improving the efficiency of electrokinetic processes.     

Investigation Static/Dynamic Surface and Interfacial Tension of Some Synthesized Polymeric Surfactants to Enhance the Egyptian Jet Fuel A1 Atomization

In the present work some exthoxylated polyalkylphenol surfactants have different alkyl chains (nonyl and dodecyl) were synthesized. The static surface tension for these surfactants in water and jet fuel A1 was measured and the critical micelle concentration (CMC) for each surfactant was determined. The data show the general trend of decreasing the CMC against the molecular weight of the synthesized polymeric surfactants. The HLB of these surfactants was also calculated. The dynamic surface tension for the synthesized surfactants was measured at CMC. The dynamic interfacial tension for these surfactants with jet fuel A1 at CMC was also measured using the spinning drop technique. The results showed that the effect of the synthesized surfactants on deceasing the time of droplet maturation was significant remarked. The decrease of this time leads to enhance of jet fuel atomization.     

Recent advances in the modeling and simulation of metallocene catalysis,sequence distribution,chain conformations,and crystallization of polymers

This article is a review describing the latest advances in modeling and simulation of polymers. Sequence distributions in stereoblock polymers and copolymers greatly affect their chain conformations and thermal transitions. While no theory was able to fully predict the influence of chain conformations on polymer crystallization, modeling techniques have shown good reliance in simulating the conformational behavior of polymeric chains and the related physical properties. This is done by generating representative sequences, and studying the chain conformation and packing of such sequences into crystalline regions in multichain systems. Metallocene catalysts, a class of single site catalysts, also showed unprecedented performance in the polymerization of olefins, most notably their activity, copolymerization capabilities, and potential for precise control of stereostructures. These attributes are among the most important issues in the manufacture of polyolefins and olefin copolymers, and are too good to be ignored. These polymers consist of alternating atactic sequences, which are amorphous and act as elastomeric chains, and ordered isotactic or syndiotactic sequences which, if long enough, will crystallize and act as physical reinforcing crosslinks. Mesoscopic investigation utilizing computer modeling and simulation into the effects of the sequence length and sequence length distribution on the reinforcement of stereoblock and stereoregular polyolefins has also been reviewed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2524–2541, 2006     

The role of particle size on the deposition efficiency of ink on plastic spheres

Experimental investigation of the effect of carbon particle size on its deposition efficiency on the surface of plastic particles has been performed in stirred vessel. A model based on Langmuir kinetics was used, and it provided a good fit for the experimental results. The effect of de-inking conditions such as, carbon particle size, calcium chloride concentration, and carbon concentration has been investigated.

Different sizes of carbon particles were tested. It was found that the deposition rate and the deposition efficiency were generally higher for the larger carbon particles.

The effect of CaCl₂ concentration on the deposition efficiency was investigated. Results showed that the deposition rate increased when the concentration of CaCl₂ increased from 0.05 to 0.10 g/l (the stochiometric ratio needed to react with sodium stearate). Moreover, the deposition efficiency was higher at this concentration. Concentrations above the stochiometric ratio did not show a systematic behavior for the deposition rate and the deposition efficiency.

Finally, the effect of carbon concentration was examined. Carbon concentration of 0.25, 0.30, and 0.40 g/l were used. Results showed that the concentration of carbon did not affect the deposition efficiency nor the rate of deposition.

This study confirmed the applicability of the method of ink removal from recycled waste paper using plastic particles, proposed by previous investigators.     

Corner-cube four-detector photopolarimeter

The four-detector photopolarimeter is operated using the compact and easier-to-align corner-cube configuration, and theoretical and experimental instrument matrices are given. Experimental results are consistent with theory. Light-beam deviation effects are also analysed and some improvement in the field of view is reported.