A stochastic approach for simulating spatially inhomogeneous coagulation dynamics in the gelation regime

We present a stochastic approach for the simulation of coagulation–diffusion dynamics in the gelation regime. The method couples the mass flow algorithm for coagulation processes with a stochastic variant of the diffusion-velocity method in a discretized framework. The simulation of the stochastic processes occurs according to an optimized implementation of the principle of grouping the possible events. A full simulation of a particle system driven by coagulation–diffusion dynamics is performed with a high degree of accuracy. This allows a qualitative and quantitative analysis of the behaviour of the system. The performance of the method becomes more evident especially in the gelation regime, where the computations become usually very time consuming.     

A highly sensitive spectrofluorometric method for the determination of a new antidepressant drug, reboxetine, in tablets

A highly sensitive, selective, and rapid spectrofluorometric method has been developed for the determination of reboxetine (REB) in tablets. The method is based on derivatization with 7-chloro-4-nitrobenzofurazan. The product showed an absorption maximum at 476 nm and a fluorescence emission peak at 533 nm in ethyl acetate. The optimum conditions of the reaction were investigated, and it was found that the reaction proceeded quantitatively at pH 8.5, 70 degrees C in 5 min. The calibration graph is rectilinear over the range of 0.02-0.40 microg/mL. The relative standard deviation values for intraday and interday precision were 0.40-0.93 and 0.54-1.37%, respectively. The proposed method was applied to the assay of REB in tablets. Mean recovery of REB from the tablets ranged between 99.91-100.20%. The results were compared statistically with those obtained by a method reported in the literature. The method is sensitive, simple, and selective, and can be used for routine quality control analysis.     

Comparison of high-performance liquid chromatography of cyclotriphosphazene derivatives with one or two equivalent stereogenic centres

High-performance liquid chromatographic (HPLC) methods have been developed for investigating the stereogenic properties of two analogous series of dibenzylamino derivatives of cyclotriphosphazene containing either one or two equivalent stereogenic centres. Separation of the enantiomers of all the racemic compounds has been investigated by chiral HPLC using Whelk-01 and Chiralcel OD columns. In all cases, conditions for separation of enantiomers have been found using a Whelk-01 column with different ratios of tetrahydrofuran in n-hexane as the mobile phase. It is found that both the separation factor (alpha) and resolution factor (R(S)) of molecules with two equivalent stereogenic centres are greater than those for analogues with only one centre.     

Comparison of helical twisting powers of novel fluorinated amphiphilic enantiomers with their hydrogenated counterparts

This is the first report on novel amphiphilic enantiomers as esters of alanine and serine with a partially fluorinated octyl chain (L-APFOE and L-SPFOE), which form intrinsic chiral nematic (N*) phases with water only and exhibit very high helical twisting powers (htps) compared to their hydrogenated counterparts, dodecylesters of L-alanine (L-ADDE) and L-serine (l-SDDE). They also exhibit a wider N* range than those known in the literature. Furthermore, the htps of the chiral dopants mandelic acid (MA) and hexahydromandelic acid (HHMA) in the racemic nematic phase of DL-SPFOE and DL-APFOE are remarkably higher than those in the hydrogenated counterparts. The tremendous increase in chirality (htps) of the same single chiral center is a new phenomenon in micellar N* phases and is attributed to a "pivot" effect of the fluoroalkyl chain. As a result, a "skewed micelle" model is proposed to explain why the htp value of L-APFOE is higher than that of L-SPFOE, and accordingly how the intermicellar chirality transfer (chiral induction) may be visualized. The simplicity of these binary mixtures and the enlargement in htp of the single chiral centers visualized as the "skewed micelle" model may provide a basis vital for future computer modeling of chiral lyotropics.     

Effect of cationic surfactant adsorption on the rheological and surface properties of bentonite dispersions

In this study, the adsorption, bridging, and intercalation effects of a cationic surfactant, benzyldimethyltetradecyl ammonium chloride (BDTDACl), on bentonite clay suspensions was investigated. The adsorption, rheological behaviors, and colloidal properties of the clay dispersions were determined as a function surfactant concentration. Adsorption isotherms were obtained using the batch-equilibrium technique. The rheological behavior of the clay suspensions was obtained by shear stress-shear rate measurements within 0-350 s-1 shear rates. The structure of the composite particles was analyzed by using X-ray diffraction analysis and it was found that the expansions of basal d-spacings are less than 16.80 A, suggesting a monolayer structure.     

C.I. Reactive Orange 16-dodecylpyridinium chloride interactions in electrolytic solutions

The effect of electrolytes on the interaction between an anionic dye and a cationic surfactant was investigated spectrophotometrically in submicellar concentration range at certain temperature. The spectral change of the azo dye C.I. Reactive Orange 16 (RO16) exhibits a high sensitivity to the polarity of dye's environment. Dodecylpyridinium chloride (DPC) affects the electronic absorption spectra of dye solution that is dye-surfactant interaction results formation of complex and therefore a decrease in maximum absorption spectra (1.577 at 494 nm). The electrolyte cations cause an increase of the absorbance of DPC-RO16 ion-pair complex in the following order: Ca(2+)>Na(+)>NH(4)(+)>K(+)>Mg(2+), also for electrolyte anions Br(-)>Cl(-)>SO(4)(2-). Furthermore, this order can be changeable with increasing electrolyte concentration. The increase on absorbance value with increasing electrolyte concentration is explained as charge screening. The increase or decrease on absorption spectra of RO16-DPC solution depends on concentration range of the electrolyte added. As an increase on absorbance value with increasing electrolyte concentration is explained as charge screening, a decrease in this value for higher concentration of electrolyte is attributed as the charge of micelle shape.     

EPR spectra of Cu2+ and VO2+ ions in ammonium hydrogen oxalate hemihydrate [(NH4)HC2O4 . (1/2)H2O] single crystals

Cu(2+) and VO(2+) doped ammonium hydrogen oxalate hemihydrate, [(NH(4))HC(2)O(4) . (1/2)H(2)O], single crystals have been studied at room temperature and at 113K in three mutually perpendicular planes. Both ions yield unexpectedly large number of lines. The calculated results of the Cu(2+) and VO(2+) doped in [(NH(4))HC(2)O(4) . (1/2)H(2)O] indicate that both ions substitute with the NH(4)(+) ion in the structure. The EPR spectra of Cu(2+) ions are characteristic of tetragonally elongated octahedral site and the spectra of VO(2+) are characteristic of tetragonally compressed complex. The angular variation of the EPR spectra has shown that two different Cu(2+) and VO(2+) complexes are located in different chemical environments, and each environment contains two magnetically inequivalent Cu(2+) and VO(2+) sites in distinct orientations occupying substitutional positions in the lattice and show very high angular dependence. The principal g and the hyperfine (A) values of both ions are determined.     

Antioxidant activity of two wild edible mushrooms (Morchella vulgaris and Morchella esculanta) from North Turkey

The ethanol extracts of Morchella vulgaris (EEMV) and Morchella esculanta (EEME) were analysed for their antioxidant activities in different systems including reducing power, free radical scavenging, superoxide anion radical scavenging, total antioxidant activity, and metal chelating activity. EEMV and EEME had similar reducing power, free radical scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, and metal chelating activity at concentrations of 50, 100, and 150 microg/mL. These various antioxidant activities were compared to standard antioxidants such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and alpha-tocopherol. The percent inhibition of different concentrations of EEMV on peroxidation in the linoleic acid system was 85 and 87 % respectively, which was greater than that of 100 and 250 microg/mL of alpha-tocopherol (50 and 77%, respectively) and similar to 250 microg/mL of BHA (85, 87%, respectively). The percent inhibition of different concentrations of EEME on peroxidation in the linoleic acid system was 80 and 87 % respectively, which was greater than that of 100 and 250 microg/mL of alpha-tocopherol (50, 77%) and similar to 250 microg/mL BHA (87%). On the other hand, the percent inhibition of 100 and 250 microg/mL of BHT was 97 and 99%, respectively. In addition, the total phenolic compounds in EEMV and EEME were determined as gallic acid equivalents.     

Projective modules and prime submodules

In this paper, we use Zorn’s Lemma, multiplicatively closed subsets and saturated closed subsets for the following two topics (i) The existence of prime submodules in some cases (ii) The proof that submodules with a certain property satisfy the radical formula. We also give a partial characterization of a submodule of a projective module which satisfies the prime property.     

The minimal genus problem in rational surfaces CP2 # n[`(CP2 )]CP^2 \# n\overline {CP^2 }

There are three key ingredients in the study of the minimal genus problem for rational surfaces : the generalized adjunction formula, the action of the orthogonal group of the Lorentz space and the geometric construction. In this paper, we prove the uniqueness of the standard form (see Definition 1.1 and Theorem 1.1) of a 2-dimensional homology class under the action of the subgroup of the Lorentz orthogonal group that is realized by the diffeomorphisms of . Using the geometric construction, we determine the minimal genera of some classes (see Theorem 1.2).